LCOV - code coverage report
Current view: top level - src/backend/storage/lmgr - predicate.c (source / functions) Hit Total Coverage
Test: PostgreSQL 18devel Lines: 983 1322 74.4 %
Date: 2025-04-24 13:15:39 Functions: 64 71 90.1 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * predicate.c
       4             :  *    POSTGRES predicate locking
       5             :  *    to support full serializable transaction isolation
       6             :  *
       7             :  *
       8             :  * The approach taken is to implement Serializable Snapshot Isolation (SSI)
       9             :  * as initially described in this paper:
      10             :  *
      11             :  *  Michael J. Cahill, Uwe Röhm, and Alan D. Fekete. 2008.
      12             :  *  Serializable isolation for snapshot databases.
      13             :  *  In SIGMOD '08: Proceedings of the 2008 ACM SIGMOD
      14             :  *  international conference on Management of data,
      15             :  *  pages 729-738, New York, NY, USA. ACM.
      16             :  *  http://doi.acm.org/10.1145/1376616.1376690
      17             :  *
      18             :  * and further elaborated in Cahill's doctoral thesis:
      19             :  *
      20             :  *  Michael James Cahill. 2009.
      21             :  *  Serializable Isolation for Snapshot Databases.
      22             :  *  Sydney Digital Theses.
      23             :  *  University of Sydney, School of Information Technologies.
      24             :  *  http://hdl.handle.net/2123/5353
      25             :  *
      26             :  *
      27             :  * Predicate locks for Serializable Snapshot Isolation (SSI) are SIREAD
      28             :  * locks, which are so different from normal locks that a distinct set of
      29             :  * structures is required to handle them.  They are needed to detect
      30             :  * rw-conflicts when the read happens before the write.  (When the write
      31             :  * occurs first, the reading transaction can check for a conflict by
      32             :  * examining the MVCC data.)
      33             :  *
      34             :  * (1)  Besides tuples actually read, they must cover ranges of tuples
      35             :  *      which would have been read based on the predicate.  This will
      36             :  *      require modelling the predicates through locks against database
      37             :  *      objects such as pages, index ranges, or entire tables.
      38             :  *
      39             :  * (2)  They must be kept in RAM for quick access.  Because of this, it
      40             :  *      isn't possible to always maintain tuple-level granularity -- when
      41             :  *      the space allocated to store these approaches exhaustion, a
      42             :  *      request for a lock may need to scan for situations where a single
      43             :  *      transaction holds many fine-grained locks which can be coalesced
      44             :  *      into a single coarser-grained lock.
      45             :  *
      46             :  * (3)  They never block anything; they are more like flags than locks
      47             :  *      in that regard; although they refer to database objects and are
      48             :  *      used to identify rw-conflicts with normal write locks.
      49             :  *
      50             :  * (4)  While they are associated with a transaction, they must survive
      51             :  *      a successful COMMIT of that transaction, and remain until all
      52             :  *      overlapping transactions complete.  This even means that they
      53             :  *      must survive termination of the transaction's process.  If a
      54             :  *      top level transaction is rolled back, however, it is immediately
      55             :  *      flagged so that it can be ignored, and its SIREAD locks can be
      56             :  *      released any time after that.
      57             :  *
      58             :  * (5)  The only transactions which create SIREAD locks or check for
      59             :  *      conflicts with them are serializable transactions.
      60             :  *
      61             :  * (6)  When a write lock for a top level transaction is found to cover
      62             :  *      an existing SIREAD lock for the same transaction, the SIREAD lock
      63             :  *      can be deleted.
      64             :  *
      65             :  * (7)  A write from a serializable transaction must ensure that an xact
      66             :  *      record exists for the transaction, with the same lifespan (until
      67             :  *      all concurrent transaction complete or the transaction is rolled
      68             :  *      back) so that rw-dependencies to that transaction can be
      69             :  *      detected.
      70             :  *
      71             :  * We use an optimization for read-only transactions. Under certain
      72             :  * circumstances, a read-only transaction's snapshot can be shown to
      73             :  * never have conflicts with other transactions.  This is referred to
      74             :  * as a "safe" snapshot (and one known not to be is "unsafe").
      75             :  * However, it can't be determined whether a snapshot is safe until
      76             :  * all concurrent read/write transactions complete.
      77             :  *
      78             :  * Once a read-only transaction is known to have a safe snapshot, it
      79             :  * can release its predicate locks and exempt itself from further
      80             :  * predicate lock tracking. READ ONLY DEFERRABLE transactions run only
      81             :  * on safe snapshots, waiting as necessary for one to be available.
      82             :  *
      83             :  *
      84             :  * Lightweight locks to manage access to the predicate locking shared
      85             :  * memory objects must be taken in this order, and should be released in
      86             :  * reverse order:
      87             :  *
      88             :  *  SerializableFinishedListLock
      89             :  *      - Protects the list of transactions which have completed but which
      90             :  *          may yet matter because they overlap still-active transactions.
      91             :  *
      92             :  *  SerializablePredicateListLock
      93             :  *      - Protects the linked list of locks held by a transaction.  Note
      94             :  *          that the locks themselves are also covered by the partition
      95             :  *          locks of their respective lock targets; this lock only affects
      96             :  *          the linked list connecting the locks related to a transaction.
      97             :  *      - All transactions share this single lock (with no partitioning).
      98             :  *      - There is never a need for a process other than the one running
      99             :  *          an active transaction to walk the list of locks held by that
     100             :  *          transaction, except parallel query workers sharing the leader's
     101             :  *          transaction.  In the parallel case, an extra per-sxact lock is
     102             :  *          taken; see below.
     103             :  *      - It is relatively infrequent that another process needs to
     104             :  *          modify the list for a transaction, but it does happen for such
     105             :  *          things as index page splits for pages with predicate locks and
     106             :  *          freeing of predicate locked pages by a vacuum process.  When
     107             :  *          removing a lock in such cases, the lock itself contains the
     108             :  *          pointers needed to remove it from the list.  When adding a
     109             :  *          lock in such cases, the lock can be added using the anchor in
     110             :  *          the transaction structure.  Neither requires walking the list.
     111             :  *      - Cleaning up the list for a terminated transaction is sometimes
     112             :  *          not done on a retail basis, in which case no lock is required.
     113             :  *      - Due to the above, a process accessing its active transaction's
     114             :  *          list always uses a shared lock, regardless of whether it is
     115             :  *          walking or maintaining the list.  This improves concurrency
     116             :  *          for the common access patterns.
     117             :  *      - A process which needs to alter the list of a transaction other
     118             :  *          than its own active transaction must acquire an exclusive
     119             :  *          lock.
     120             :  *
     121             :  *  SERIALIZABLEXACT's member 'perXactPredicateListLock'
     122             :  *      - Protects the linked list of predicate locks held by a transaction.
     123             :  *          Only needed for parallel mode, where multiple backends share the
     124             :  *          same SERIALIZABLEXACT object.  Not needed if
     125             :  *          SerializablePredicateListLock is held exclusively.
     126             :  *
     127             :  *  PredicateLockHashPartitionLock(hashcode)
     128             :  *      - The same lock protects a target, all locks on that target, and
     129             :  *          the linked list of locks on the target.
     130             :  *      - When more than one is needed, acquire in ascending address order.
     131             :  *      - When all are needed (rare), acquire in ascending index order with
     132             :  *          PredicateLockHashPartitionLockByIndex(index).
     133             :  *
     134             :  *  SerializableXactHashLock
     135             :  *      - Protects both PredXact and SerializableXidHash.
     136             :  *
     137             :  *  SerialControlLock
     138             :  *      - Protects SerialControlData members
     139             :  *
     140             :  *  SLRU per-bank locks
     141             :  *      - Protects SerialSlruCtl
     142             :  *
     143             :  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
     144             :  * Portions Copyright (c) 1994, Regents of the University of California
     145             :  *
     146             :  *
     147             :  * IDENTIFICATION
     148             :  *    src/backend/storage/lmgr/predicate.c
     149             :  *
     150             :  *-------------------------------------------------------------------------
     151             :  */
     152             : /*
     153             :  * INTERFACE ROUTINES
     154             :  *
     155             :  * housekeeping for setting up shared memory predicate lock structures
     156             :  *      PredicateLockShmemInit(void)
     157             :  *      PredicateLockShmemSize(void)
     158             :  *
     159             :  * predicate lock reporting
     160             :  *      GetPredicateLockStatusData(void)
     161             :  *      PageIsPredicateLocked(Relation relation, BlockNumber blkno)
     162             :  *
     163             :  * predicate lock maintenance
     164             :  *      GetSerializableTransactionSnapshot(Snapshot snapshot)
     165             :  *      SetSerializableTransactionSnapshot(Snapshot snapshot,
     166             :  *                                         VirtualTransactionId *sourcevxid)
     167             :  *      RegisterPredicateLockingXid(void)
     168             :  *      PredicateLockRelation(Relation relation, Snapshot snapshot)
     169             :  *      PredicateLockPage(Relation relation, BlockNumber blkno,
     170             :  *                      Snapshot snapshot)
     171             :  *      PredicateLockTID(Relation relation, ItemPointer tid, Snapshot snapshot,
     172             :  *                       TransactionId tuple_xid)
     173             :  *      PredicateLockPageSplit(Relation relation, BlockNumber oldblkno,
     174             :  *                             BlockNumber newblkno)
     175             :  *      PredicateLockPageCombine(Relation relation, BlockNumber oldblkno,
     176             :  *                               BlockNumber newblkno)
     177             :  *      TransferPredicateLocksToHeapRelation(Relation relation)
     178             :  *      ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe)
     179             :  *
     180             :  * conflict detection (may also trigger rollback)
     181             :  *      CheckForSerializableConflictOut(Relation relation, TransactionId xid,
     182             :  *                                      Snapshot snapshot)
     183             :  *      CheckForSerializableConflictIn(Relation relation, ItemPointer tid,
     184             :  *                                     BlockNumber blkno)
     185             :  *      CheckTableForSerializableConflictIn(Relation relation)
     186             :  *
     187             :  * final rollback checking
     188             :  *      PreCommit_CheckForSerializationFailure(void)
     189             :  *
     190             :  * two-phase commit support
     191             :  *      AtPrepare_PredicateLocks(void);
     192             :  *      PostPrepare_PredicateLocks(TransactionId xid);
     193             :  *      PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit);
     194             :  *      predicatelock_twophase_recover(TransactionId xid, uint16 info,
     195             :  *                                     void *recdata, uint32 len);
     196             :  */
     197             : 
     198             : #include "postgres.h"
     199             : 
     200             : #include "access/parallel.h"
     201             : #include "access/slru.h"
     202             : #include "access/transam.h"
     203             : #include "access/twophase.h"
     204             : #include "access/twophase_rmgr.h"
     205             : #include "access/xact.h"
     206             : #include "access/xlog.h"
     207             : #include "miscadmin.h"
     208             : #include "pgstat.h"
     209             : #include "port/pg_lfind.h"
     210             : #include "storage/predicate.h"
     211             : #include "storage/predicate_internals.h"
     212             : #include "storage/proc.h"
     213             : #include "storage/procarray.h"
     214             : #include "utils/guc_hooks.h"
     215             : #include "utils/rel.h"
     216             : #include "utils/snapmgr.h"
     217             : 
     218             : /* Uncomment the next line to test the graceful degradation code. */
     219             : /* #define TEST_SUMMARIZE_SERIAL */
     220             : 
     221             : /*
     222             :  * Test the most selective fields first, for performance.
     223             :  *
     224             :  * a is covered by b if all of the following hold:
     225             :  *  1) a.database = b.database
     226             :  *  2) a.relation = b.relation
     227             :  *  3) b.offset is invalid (b is page-granularity or higher)
     228             :  *  4) either of the following:
     229             :  *      4a) a.offset is valid (a is tuple-granularity) and a.page = b.page
     230             :  *   or 4b) a.offset is invalid and b.page is invalid (a is
     231             :  *          page-granularity and b is relation-granularity
     232             :  */
     233             : #define TargetTagIsCoveredBy(covered_target, covering_target)           \
     234             :     ((GET_PREDICATELOCKTARGETTAG_RELATION(covered_target) == /* (2) */  \
     235             :       GET_PREDICATELOCKTARGETTAG_RELATION(covering_target))             \
     236             :      && (GET_PREDICATELOCKTARGETTAG_OFFSET(covering_target) ==          \
     237             :          InvalidOffsetNumber)                                /* (3) */  \
     238             :      && (((GET_PREDICATELOCKTARGETTAG_OFFSET(covered_target) !=         \
     239             :            InvalidOffsetNumber)                              /* (4a) */ \
     240             :           && (GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) ==       \
     241             :               GET_PREDICATELOCKTARGETTAG_PAGE(covered_target)))         \
     242             :          || ((GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) ==       \
     243             :               InvalidBlockNumber)                            /* (4b) */ \
     244             :              && (GET_PREDICATELOCKTARGETTAG_PAGE(covered_target)        \
     245             :                  != InvalidBlockNumber)))                               \
     246             :      && (GET_PREDICATELOCKTARGETTAG_DB(covered_target) ==    /* (1) */  \
     247             :          GET_PREDICATELOCKTARGETTAG_DB(covering_target)))
     248             : 
     249             : /*
     250             :  * The predicate locking target and lock shared hash tables are partitioned to
     251             :  * reduce contention.  To determine which partition a given target belongs to,
     252             :  * compute the tag's hash code with PredicateLockTargetTagHashCode(), then
     253             :  * apply one of these macros.
     254             :  * NB: NUM_PREDICATELOCK_PARTITIONS must be a power of 2!
     255             :  */
     256             : #define PredicateLockHashPartition(hashcode) \
     257             :     ((hashcode) % NUM_PREDICATELOCK_PARTITIONS)
     258             : #define PredicateLockHashPartitionLock(hashcode) \
     259             :     (&MainLWLockArray[PREDICATELOCK_MANAGER_LWLOCK_OFFSET + \
     260             :         PredicateLockHashPartition(hashcode)].lock)
     261             : #define PredicateLockHashPartitionLockByIndex(i) \
     262             :     (&MainLWLockArray[PREDICATELOCK_MANAGER_LWLOCK_OFFSET + (i)].lock)
     263             : 
     264             : #define NPREDICATELOCKTARGETENTS() \
     265             :     mul_size(max_predicate_locks_per_xact, add_size(MaxBackends, max_prepared_xacts))
     266             : 
     267             : #define SxactIsOnFinishedList(sxact) (!dlist_node_is_detached(&(sxact)->finishedLink))
     268             : 
     269             : /*
     270             :  * Note that a sxact is marked "prepared" once it has passed
     271             :  * PreCommit_CheckForSerializationFailure, even if it isn't using
     272             :  * 2PC. This is the point at which it can no longer be aborted.
     273             :  *
     274             :  * The PREPARED flag remains set after commit, so SxactIsCommitted
     275             :  * implies SxactIsPrepared.
     276             :  */
     277             : #define SxactIsCommitted(sxact) (((sxact)->flags & SXACT_FLAG_COMMITTED) != 0)
     278             : #define SxactIsPrepared(sxact) (((sxact)->flags & SXACT_FLAG_PREPARED) != 0)
     279             : #define SxactIsRolledBack(sxact) (((sxact)->flags & SXACT_FLAG_ROLLED_BACK) != 0)
     280             : #define SxactIsDoomed(sxact) (((sxact)->flags & SXACT_FLAG_DOOMED) != 0)
     281             : #define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0)
     282             : #define SxactHasSummaryConflictIn(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_IN) != 0)
     283             : #define SxactHasSummaryConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_OUT) != 0)
     284             : /*
     285             :  * The following macro actually means that the specified transaction has a
     286             :  * conflict out *to a transaction which committed ahead of it*.  It's hard
     287             :  * to get that into a name of a reasonable length.
     288             :  */
     289             : #define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0)
     290             : #define SxactIsDeferrableWaiting(sxact) (((sxact)->flags & SXACT_FLAG_DEFERRABLE_WAITING) != 0)
     291             : #define SxactIsROSafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_SAFE) != 0)
     292             : #define SxactIsROUnsafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_UNSAFE) != 0)
     293             : #define SxactIsPartiallyReleased(sxact) (((sxact)->flags & SXACT_FLAG_PARTIALLY_RELEASED) != 0)
     294             : 
     295             : /*
     296             :  * Compute the hash code associated with a PREDICATELOCKTARGETTAG.
     297             :  *
     298             :  * To avoid unnecessary recomputations of the hash code, we try to do this
     299             :  * just once per function, and then pass it around as needed.  Aside from
     300             :  * passing the hashcode to hash_search_with_hash_value(), we can extract
     301             :  * the lock partition number from the hashcode.
     302             :  */
     303             : #define PredicateLockTargetTagHashCode(predicatelocktargettag) \
     304             :     get_hash_value(PredicateLockTargetHash, predicatelocktargettag)
     305             : 
     306             : /*
     307             :  * Given a predicate lock tag, and the hash for its target,
     308             :  * compute the lock hash.
     309             :  *
     310             :  * To make the hash code also depend on the transaction, we xor the sxid
     311             :  * struct's address into the hash code, left-shifted so that the
     312             :  * partition-number bits don't change.  Since this is only a hash, we
     313             :  * don't care if we lose high-order bits of the address; use an
     314             :  * intermediate variable to suppress cast-pointer-to-int warnings.
     315             :  */
     316             : #define PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash) \
     317             :     ((targethash) ^ ((uint32) PointerGetDatum((predicatelocktag)->myXact)) \
     318             :      << LOG2_NUM_PREDICATELOCK_PARTITIONS)
     319             : 
     320             : 
     321             : /*
     322             :  * The SLRU buffer area through which we access the old xids.
     323             :  */
     324             : static SlruCtlData SerialSlruCtlData;
     325             : 
     326             : #define SerialSlruCtl           (&SerialSlruCtlData)
     327             : 
     328             : #define SERIAL_PAGESIZE         BLCKSZ
     329             : #define SERIAL_ENTRYSIZE            sizeof(SerCommitSeqNo)
     330             : #define SERIAL_ENTRIESPERPAGE   (SERIAL_PAGESIZE / SERIAL_ENTRYSIZE)
     331             : 
     332             : /*
     333             :  * Set maximum pages based on the number needed to track all transactions.
     334             :  */
     335             : #define SERIAL_MAX_PAGE         (MaxTransactionId / SERIAL_ENTRIESPERPAGE)
     336             : 
     337             : #define SerialNextPage(page) (((page) >= SERIAL_MAX_PAGE) ? 0 : (page) + 1)
     338             : 
     339             : #define SerialValue(slotno, xid) (*((SerCommitSeqNo *) \
     340             :     (SerialSlruCtl->shared->page_buffer[slotno] + \
     341             :     ((((uint32) (xid)) % SERIAL_ENTRIESPERPAGE) * SERIAL_ENTRYSIZE))))
     342             : 
     343             : #define SerialPage(xid) (((uint32) (xid)) / SERIAL_ENTRIESPERPAGE)
     344             : 
     345             : typedef struct SerialControlData
     346             : {
     347             :     int64       headPage;       /* newest initialized page */
     348             :     TransactionId headXid;      /* newest valid Xid in the SLRU */
     349             :     TransactionId tailXid;      /* oldest xmin we might be interested in */
     350             : }           SerialControlData;
     351             : 
     352             : typedef struct SerialControlData *SerialControl;
     353             : 
     354             : static SerialControl serialControl;
     355             : 
     356             : /*
     357             :  * When the oldest committed transaction on the "finished" list is moved to
     358             :  * SLRU, its predicate locks will be moved to this "dummy" transaction,
     359             :  * collapsing duplicate targets.  When a duplicate is found, the later
     360             :  * commitSeqNo is used.
     361             :  */
     362             : static SERIALIZABLEXACT *OldCommittedSxact;
     363             : 
     364             : 
     365             : /*
     366             :  * These configuration variables are used to set the predicate lock table size
     367             :  * and to control promotion of predicate locks to coarser granularity in an
     368             :  * attempt to degrade performance (mostly as false positive serialization
     369             :  * failure) gracefully in the face of memory pressure.
     370             :  */
     371             : int         max_predicate_locks_per_xact;   /* in guc_tables.c */
     372             : int         max_predicate_locks_per_relation;   /* in guc_tables.c */
     373             : int         max_predicate_locks_per_page;   /* in guc_tables.c */
     374             : 
     375             : /*
     376             :  * This provides a list of objects in order to track transactions
     377             :  * participating in predicate locking.  Entries in the list are fixed size,
     378             :  * and reside in shared memory.  The memory address of an entry must remain
     379             :  * fixed during its lifetime.  The list will be protected from concurrent
     380             :  * update externally; no provision is made in this code to manage that.  The
     381             :  * number of entries in the list, and the size allowed for each entry is
     382             :  * fixed upon creation.
     383             :  */
     384             : static PredXactList PredXact;
     385             : 
     386             : /*
     387             :  * This provides a pool of RWConflict data elements to use in conflict lists
     388             :  * between transactions.
     389             :  */
     390             : static RWConflictPoolHeader RWConflictPool;
     391             : 
     392             : /*
     393             :  * The predicate locking hash tables are in shared memory.
     394             :  * Each backend keeps pointers to them.
     395             :  */
     396             : static HTAB *SerializableXidHash;
     397             : static HTAB *PredicateLockTargetHash;
     398             : static HTAB *PredicateLockHash;
     399             : static dlist_head *FinishedSerializableTransactions;
     400             : 
     401             : /*
     402             :  * Tag for a dummy entry in PredicateLockTargetHash. By temporarily removing
     403             :  * this entry, you can ensure that there's enough scratch space available for
     404             :  * inserting one entry in the hash table. This is an otherwise-invalid tag.
     405             :  */
     406             : static const PREDICATELOCKTARGETTAG ScratchTargetTag = {0, 0, 0, 0};
     407             : static uint32 ScratchTargetTagHash;
     408             : static LWLock *ScratchPartitionLock;
     409             : 
     410             : /*
     411             :  * The local hash table used to determine when to combine multiple fine-
     412             :  * grained locks into a single courser-grained lock.
     413             :  */
     414             : static HTAB *LocalPredicateLockHash = NULL;
     415             : 
     416             : /*
     417             :  * Keep a pointer to the currently-running serializable transaction (if any)
     418             :  * for quick reference. Also, remember if we have written anything that could
     419             :  * cause a rw-conflict.
     420             :  */
     421             : static SERIALIZABLEXACT *MySerializableXact = InvalidSerializableXact;
     422             : static bool MyXactDidWrite = false;
     423             : 
     424             : /*
     425             :  * The SXACT_FLAG_RO_UNSAFE optimization might lead us to release
     426             :  * MySerializableXact early.  If that happens in a parallel query, the leader
     427             :  * needs to defer the destruction of the SERIALIZABLEXACT until end of
     428             :  * transaction, because the workers still have a reference to it.  In that
     429             :  * case, the leader stores it here.
     430             :  */
     431             : static SERIALIZABLEXACT *SavedSerializableXact = InvalidSerializableXact;
     432             : 
     433             : /* local functions */
     434             : 
     435             : static SERIALIZABLEXACT *CreatePredXact(void);
     436             : static void ReleasePredXact(SERIALIZABLEXACT *sxact);
     437             : 
     438             : static bool RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer);
     439             : static void SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer);
     440             : static void SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, SERIALIZABLEXACT *activeXact);
     441             : static void ReleaseRWConflict(RWConflict conflict);
     442             : static void FlagSxactUnsafe(SERIALIZABLEXACT *sxact);
     443             : 
     444             : static bool SerialPagePrecedesLogically(int64 page1, int64 page2);
     445             : static void SerialInit(void);
     446             : static void SerialAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo);
     447             : static SerCommitSeqNo SerialGetMinConflictCommitSeqNo(TransactionId xid);
     448             : static void SerialSetActiveSerXmin(TransactionId xid);
     449             : 
     450             : static uint32 predicatelock_hash(const void *key, Size keysize);
     451             : static void SummarizeOldestCommittedSxact(void);
     452             : static Snapshot GetSafeSnapshot(Snapshot origSnapshot);
     453             : static Snapshot GetSerializableTransactionSnapshotInt(Snapshot snapshot,
     454             :                                                       VirtualTransactionId *sourcevxid,
     455             :                                                       int sourcepid);
     456             : static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag);
     457             : static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag,
     458             :                                       PREDICATELOCKTARGETTAG *parent);
     459             : static bool CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag);
     460             : static void RemoveScratchTarget(bool lockheld);
     461             : static void RestoreScratchTarget(bool lockheld);
     462             : static void RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target,
     463             :                                        uint32 targettaghash);
     464             : static void DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag);
     465             : static int  MaxPredicateChildLocks(const PREDICATELOCKTARGETTAG *tag);
     466             : static bool CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag);
     467             : static void DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag);
     468             : static void CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag,
     469             :                                 uint32 targettaghash,
     470             :                                 SERIALIZABLEXACT *sxact);
     471             : static void DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash);
     472             : static bool TransferPredicateLocksToNewTarget(PREDICATELOCKTARGETTAG oldtargettag,
     473             :                                               PREDICATELOCKTARGETTAG newtargettag,
     474             :                                               bool removeOld);
     475             : static void PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag);
     476             : static void DropAllPredicateLocksFromTable(Relation relation,
     477             :                                            bool transfer);
     478             : static void SetNewSxactGlobalXmin(void);
     479             : static void ClearOldPredicateLocks(void);
     480             : static void ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
     481             :                                        bool summarize);
     482             : static bool XidIsConcurrent(TransactionId xid);
     483             : static void CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag);
     484             : static void FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer);
     485             : static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
     486             :                                                     SERIALIZABLEXACT *writer);
     487             : static void CreateLocalPredicateLockHash(void);
     488             : static void ReleasePredicateLocksLocal(void);
     489             : 
     490             : 
     491             : /*------------------------------------------------------------------------*/
     492             : 
     493             : /*
     494             :  * Does this relation participate in predicate locking? Temporary and system
     495             :  * relations are exempt.
     496             :  */
     497             : static inline bool
     498      308994 : PredicateLockingNeededForRelation(Relation relation)
     499             : {
     500      423276 :     return !(relation->rd_id < FirstUnpinnedObjectId ||
     501      114282 :              RelationUsesLocalBuffers(relation));
     502             : }
     503             : 
     504             : /*
     505             :  * When a public interface method is called for a read, this is the test to
     506             :  * see if we should do a quick return.
     507             :  *
     508             :  * Note: this function has side-effects! If this transaction has been flagged
     509             :  * as RO-safe since the last call, we release all predicate locks and reset
     510             :  * MySerializableXact. That makes subsequent calls to return quickly.
     511             :  *
     512             :  * This is marked as 'inline' to eliminate the function call overhead in the
     513             :  * common case that serialization is not needed.
     514             :  */
     515             : static inline bool
     516   120983350 : SerializationNeededForRead(Relation relation, Snapshot snapshot)
     517             : {
     518             :     /* Nothing to do if this is not a serializable transaction */
     519   120983350 :     if (MySerializableXact == InvalidSerializableXact)
     520   120685600 :         return false;
     521             : 
     522             :     /*
     523             :      * Don't acquire locks or conflict when scanning with a special snapshot.
     524             :      * This excludes things like CLUSTER and REINDEX. They use the wholesale
     525             :      * functions TransferPredicateLocksToHeapRelation() and
     526             :      * CheckTableForSerializableConflictIn() to participate in serialization,
     527             :      * but the scans involved don't need serialization.
     528             :      */
     529      297750 :     if (!IsMVCCSnapshot(snapshot))
     530        3214 :         return false;
     531             : 
     532             :     /*
     533             :      * Check if we have just become "RO-safe". If we have, immediately release
     534             :      * all locks as they're not needed anymore. This also resets
     535             :      * MySerializableXact, so that subsequent calls to this function can exit
     536             :      * quickly.
     537             :      *
     538             :      * A transaction is flagged as RO_SAFE if all concurrent R/W transactions
     539             :      * commit without having conflicts out to an earlier snapshot, thus
     540             :      * ensuring that no conflicts are possible for this transaction.
     541             :      */
     542      294536 :     if (SxactIsROSafe(MySerializableXact))
     543             :     {
     544          66 :         ReleasePredicateLocks(false, true);
     545          66 :         return false;
     546             :     }
     547             : 
     548             :     /* Check if the relation doesn't participate in predicate locking */
     549      294470 :     if (!PredicateLockingNeededForRelation(relation))
     550      189636 :         return false;
     551             : 
     552      104834 :     return true;                /* no excuse to skip predicate locking */
     553             : }
     554             : 
     555             : /*
     556             :  * Like SerializationNeededForRead(), but called on writes.
     557             :  * The logic is the same, but there is no snapshot and we can't be RO-safe.
     558             :  */
     559             : static inline bool
     560    33032170 : SerializationNeededForWrite(Relation relation)
     561             : {
     562             :     /* Nothing to do if this is not a serializable transaction */
     563    33032170 :     if (MySerializableXact == InvalidSerializableXact)
     564    33017996 :         return false;
     565             : 
     566             :     /* Check if the relation doesn't participate in predicate locking */
     567       14174 :     if (!PredicateLockingNeededForRelation(relation))
     568        5318 :         return false;
     569             : 
     570        8856 :     return true;                /* no excuse to skip predicate locking */
     571             : }
     572             : 
     573             : 
     574             : /*------------------------------------------------------------------------*/
     575             : 
     576             : /*
     577             :  * These functions are a simple implementation of a list for this specific
     578             :  * type of struct.  If there is ever a generalized shared memory list, we
     579             :  * should probably switch to that.
     580             :  */
     581             : static SERIALIZABLEXACT *
     582        5382 : CreatePredXact(void)
     583             : {
     584             :     SERIALIZABLEXACT *sxact;
     585             : 
     586        5382 :     if (dlist_is_empty(&PredXact->availableList))
     587           0 :         return NULL;
     588             : 
     589        5382 :     sxact = dlist_container(SERIALIZABLEXACT, xactLink,
     590             :                             dlist_pop_head_node(&PredXact->availableList));
     591        5382 :     dlist_push_tail(&PredXact->activeList, &sxact->xactLink);
     592        5382 :     return sxact;
     593             : }
     594             : 
     595             : static void
     596        3282 : ReleasePredXact(SERIALIZABLEXACT *sxact)
     597             : {
     598             :     Assert(ShmemAddrIsValid(sxact));
     599             : 
     600        3282 :     dlist_delete(&sxact->xactLink);
     601        3282 :     dlist_push_tail(&PredXact->availableList, &sxact->xactLink);
     602        3282 : }
     603             : 
     604             : /*------------------------------------------------------------------------*/
     605             : 
     606             : /*
     607             :  * These functions manage primitive access to the RWConflict pool and lists.
     608             :  */
     609             : static bool
     610        3736 : RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer)
     611             : {
     612             :     dlist_iter  iter;
     613             : 
     614             :     Assert(reader != writer);
     615             : 
     616             :     /* Check the ends of the purported conflict first. */
     617        3736 :     if (SxactIsDoomed(reader)
     618        3736 :         || SxactIsDoomed(writer)
     619        3736 :         || dlist_is_empty(&reader->outConflicts)
     620        1134 :         || dlist_is_empty(&writer->inConflicts))
     621        2682 :         return false;
     622             : 
     623             :     /*
     624             :      * A conflict is possible; walk the list to find out.
     625             :      *
     626             :      * The unconstify is needed as we have no const version of
     627             :      * dlist_foreach().
     628             :      */
     629        1086 :     dlist_foreach(iter, &unconstify(SERIALIZABLEXACT *, reader)->outConflicts)
     630             :     {
     631        1054 :         RWConflict  conflict =
     632        1054 :             dlist_container(RWConflictData, outLink, iter.cur);
     633             : 
     634        1054 :         if (conflict->sxactIn == writer)
     635        1022 :             return true;
     636             :     }
     637             : 
     638             :     /* No conflict found. */
     639          32 :     return false;
     640             : }
     641             : 
     642             : static void
     643        1560 : SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer)
     644             : {
     645             :     RWConflict  conflict;
     646             : 
     647             :     Assert(reader != writer);
     648             :     Assert(!RWConflictExists(reader, writer));
     649             : 
     650        1560 :     if (dlist_is_empty(&RWConflictPool->availableList))
     651           0 :         ereport(ERROR,
     652             :                 (errcode(ERRCODE_OUT_OF_MEMORY),
     653             :                  errmsg("not enough elements in RWConflictPool to record a read/write conflict"),
     654             :                  errhint("You might need to run fewer transactions at a time or increase \"max_connections\".")));
     655             : 
     656        1560 :     conflict = dlist_head_element(RWConflictData, outLink, &RWConflictPool->availableList);
     657        1560 :     dlist_delete(&conflict->outLink);
     658             : 
     659        1560 :     conflict->sxactOut = reader;
     660        1560 :     conflict->sxactIn = writer;
     661        1560 :     dlist_push_tail(&reader->outConflicts, &conflict->outLink);
     662        1560 :     dlist_push_tail(&writer->inConflicts, &conflict->inLink);
     663        1560 : }
     664             : 
     665             : static void
     666         264 : SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact,
     667             :                           SERIALIZABLEXACT *activeXact)
     668             : {
     669             :     RWConflict  conflict;
     670             : 
     671             :     Assert(roXact != activeXact);
     672             :     Assert(SxactIsReadOnly(roXact));
     673             :     Assert(!SxactIsReadOnly(activeXact));
     674             : 
     675         264 :     if (dlist_is_empty(&RWConflictPool->availableList))
     676           0 :         ereport(ERROR,
     677             :                 (errcode(ERRCODE_OUT_OF_MEMORY),
     678             :                  errmsg("not enough elements in RWConflictPool to record a potential read/write conflict"),
     679             :                  errhint("You might need to run fewer transactions at a time or increase \"max_connections\".")));
     680             : 
     681         264 :     conflict = dlist_head_element(RWConflictData, outLink, &RWConflictPool->availableList);
     682         264 :     dlist_delete(&conflict->outLink);
     683             : 
     684         264 :     conflict->sxactOut = activeXact;
     685         264 :     conflict->sxactIn = roXact;
     686         264 :     dlist_push_tail(&activeXact->possibleUnsafeConflicts, &conflict->outLink);
     687         264 :     dlist_push_tail(&roXact->possibleUnsafeConflicts, &conflict->inLink);
     688         264 : }
     689             : 
     690             : static void
     691        1824 : ReleaseRWConflict(RWConflict conflict)
     692             : {
     693        1824 :     dlist_delete(&conflict->inLink);
     694        1824 :     dlist_delete(&conflict->outLink);
     695        1824 :     dlist_push_tail(&RWConflictPool->availableList, &conflict->outLink);
     696        1824 : }
     697             : 
     698             : static void
     699           6 : FlagSxactUnsafe(SERIALIZABLEXACT *sxact)
     700             : {
     701             :     dlist_mutable_iter iter;
     702             : 
     703             :     Assert(SxactIsReadOnly(sxact));
     704             :     Assert(!SxactIsROSafe(sxact));
     705             : 
     706           6 :     sxact->flags |= SXACT_FLAG_RO_UNSAFE;
     707             : 
     708             :     /*
     709             :      * We know this isn't a safe snapshot, so we can stop looking for other
     710             :      * potential conflicts.
     711             :      */
     712          12 :     dlist_foreach_modify(iter, &sxact->possibleUnsafeConflicts)
     713             :     {
     714           6 :         RWConflict  conflict =
     715           6 :             dlist_container(RWConflictData, inLink, iter.cur);
     716             : 
     717             :         Assert(!SxactIsReadOnly(conflict->sxactOut));
     718             :         Assert(sxact == conflict->sxactIn);
     719             : 
     720           6 :         ReleaseRWConflict(conflict);
     721             :     }
     722           6 : }
     723             : 
     724             : /*------------------------------------------------------------------------*/
     725             : 
     726             : /*
     727             :  * Decide whether a Serial page number is "older" for truncation purposes.
     728             :  * Analogous to CLOGPagePrecedes().
     729             :  */
     730             : static bool
     731           0 : SerialPagePrecedesLogically(int64 page1, int64 page2)
     732             : {
     733             :     TransactionId xid1;
     734             :     TransactionId xid2;
     735             : 
     736           0 :     xid1 = ((TransactionId) page1) * SERIAL_ENTRIESPERPAGE;
     737           0 :     xid1 += FirstNormalTransactionId + 1;
     738           0 :     xid2 = ((TransactionId) page2) * SERIAL_ENTRIESPERPAGE;
     739           0 :     xid2 += FirstNormalTransactionId + 1;
     740             : 
     741           0 :     return (TransactionIdPrecedes(xid1, xid2) &&
     742           0 :             TransactionIdPrecedes(xid1, xid2 + SERIAL_ENTRIESPERPAGE - 1));
     743             : }
     744             : 
     745             : #ifdef USE_ASSERT_CHECKING
     746             : static void
     747             : SerialPagePrecedesLogicallyUnitTests(void)
     748             : {
     749             :     int         per_page = SERIAL_ENTRIESPERPAGE,
     750             :                 offset = per_page / 2;
     751             :     int64       newestPage,
     752             :                 oldestPage,
     753             :                 headPage,
     754             :                 targetPage;
     755             :     TransactionId newestXact,
     756             :                 oldestXact;
     757             : 
     758             :     /* GetNewTransactionId() has assigned the last XID it can safely use. */
     759             :     newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1;    /* nothing special */
     760             :     newestXact = newestPage * per_page + offset;
     761             :     Assert(newestXact / per_page == newestPage);
     762             :     oldestXact = newestXact + 1;
     763             :     oldestXact -= 1U << 31;
     764             :     oldestPage = oldestXact / per_page;
     765             : 
     766             :     /*
     767             :      * In this scenario, the SLRU headPage pertains to the last ~1000 XIDs
     768             :      * assigned.  oldestXact finishes, ~2B XIDs having elapsed since it
     769             :      * started.  Further transactions cause us to summarize oldestXact to
     770             :      * tailPage.  Function must return false so SerialAdd() doesn't zero
     771             :      * tailPage (which may contain entries for other old, recently-finished
     772             :      * XIDs) and half the SLRU.  Reaching this requires burning ~2B XIDs in
     773             :      * single-user mode, a negligible possibility.
     774             :      */
     775             :     headPage = newestPage;
     776             :     targetPage = oldestPage;
     777             :     Assert(!SerialPagePrecedesLogically(headPage, targetPage));
     778             : 
     779             :     /*
     780             :      * In this scenario, the SLRU headPage pertains to oldestXact.  We're
     781             :      * summarizing an XID near newestXact.  (Assume few other XIDs used
     782             :      * SERIALIZABLE, hence the minimal headPage advancement.  Assume
     783             :      * oldestXact was long-running and only recently reached the SLRU.)
     784             :      * Function must return true to make SerialAdd() create targetPage.
     785             :      *
     786             :      * Today's implementation mishandles this case, but it doesn't matter
     787             :      * enough to fix.  Verify that the defect affects just one page by
     788             :      * asserting correct treatment of its prior page.  Reaching this case
     789             :      * requires burning ~2B XIDs in single-user mode, a negligible
     790             :      * possibility.  Moreover, if it does happen, the consequence would be
     791             :      * mild, namely a new transaction failing in SimpleLruReadPage().
     792             :      */
     793             :     headPage = oldestPage;
     794             :     targetPage = newestPage;
     795             :     Assert(SerialPagePrecedesLogically(headPage, targetPage - 1));
     796             : #if 0
     797             :     Assert(SerialPagePrecedesLogically(headPage, targetPage));
     798             : #endif
     799             : }
     800             : #endif
     801             : 
     802             : /*
     803             :  * Initialize for the tracking of old serializable committed xids.
     804             :  */
     805             : static void
     806        2100 : SerialInit(void)
     807             : {
     808             :     bool        found;
     809             : 
     810             :     /*
     811             :      * Set up SLRU management of the pg_serial data.
     812             :      */
     813        2100 :     SerialSlruCtl->PagePrecedes = SerialPagePrecedesLogically;
     814        2100 :     SimpleLruInit(SerialSlruCtl, "serializable",
     815             :                   serializable_buffers, 0, "pg_serial",
     816             :                   LWTRANCHE_SERIAL_BUFFER, LWTRANCHE_SERIAL_SLRU,
     817             :                   SYNC_HANDLER_NONE, false);
     818             : #ifdef USE_ASSERT_CHECKING
     819             :     SerialPagePrecedesLogicallyUnitTests();
     820             : #endif
     821             :     SlruPagePrecedesUnitTests(SerialSlruCtl, SERIAL_ENTRIESPERPAGE);
     822             : 
     823             :     /*
     824             :      * Create or attach to the SerialControl structure.
     825             :      */
     826        2100 :     serialControl = (SerialControl)
     827        2100 :         ShmemInitStruct("SerialControlData", sizeof(SerialControlData), &found);
     828             : 
     829             :     Assert(found == IsUnderPostmaster);
     830        2100 :     if (!found)
     831             :     {
     832             :         /*
     833             :          * Set control information to reflect empty SLRU.
     834             :          */
     835        2100 :         LWLockAcquire(SerialControlLock, LW_EXCLUSIVE);
     836        2100 :         serialControl->headPage = -1;
     837        2100 :         serialControl->headXid = InvalidTransactionId;
     838        2100 :         serialControl->tailXid = InvalidTransactionId;
     839        2100 :         LWLockRelease(SerialControlLock);
     840             :     }
     841        2100 : }
     842             : 
     843             : /*
     844             :  * GUC check_hook for serializable_buffers
     845             :  */
     846             : bool
     847        2168 : check_serial_buffers(int *newval, void **extra, GucSource source)
     848             : {
     849        2168 :     return check_slru_buffers("serializable_buffers", newval);
     850             : }
     851             : 
     852             : /*
     853             :  * Record a committed read write serializable xid and the minimum
     854             :  * commitSeqNo of any transactions to which this xid had a rw-conflict out.
     855             :  * An invalid commitSeqNo means that there were no conflicts out from xid.
     856             :  */
     857             : static void
     858           0 : SerialAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
     859             : {
     860             :     TransactionId tailXid;
     861             :     int64       targetPage;
     862             :     int         slotno;
     863             :     int64       firstZeroPage;
     864             :     bool        isNewPage;
     865             :     LWLock     *lock;
     866             : 
     867             :     Assert(TransactionIdIsValid(xid));
     868             : 
     869           0 :     targetPage = SerialPage(xid);
     870           0 :     lock = SimpleLruGetBankLock(SerialSlruCtl, targetPage);
     871             : 
     872             :     /*
     873             :      * In this routine, we must hold both SerialControlLock and the SLRU bank
     874             :      * lock simultaneously while making the SLRU data catch up with the new
     875             :      * state that we determine.
     876             :      */
     877           0 :     LWLockAcquire(SerialControlLock, LW_EXCLUSIVE);
     878             : 
     879             :     /*
     880             :      * If 'xid' is older than the global xmin (== tailXid), there's no need to
     881             :      * store it, after all. This can happen if the oldest transaction holding
     882             :      * back the global xmin just finished, making 'xid' uninteresting, but
     883             :      * ClearOldPredicateLocks() has not yet run.
     884             :      */
     885           0 :     tailXid = serialControl->tailXid;
     886           0 :     if (!TransactionIdIsValid(tailXid) || TransactionIdPrecedes(xid, tailXid))
     887             :     {
     888           0 :         LWLockRelease(SerialControlLock);
     889           0 :         return;
     890             :     }
     891             : 
     892             :     /*
     893             :      * If the SLRU is currently unused, zero out the whole active region from
     894             :      * tailXid to headXid before taking it into use. Otherwise zero out only
     895             :      * any new pages that enter the tailXid-headXid range as we advance
     896             :      * headXid.
     897             :      */
     898           0 :     if (serialControl->headPage < 0)
     899             :     {
     900           0 :         firstZeroPage = SerialPage(tailXid);
     901           0 :         isNewPage = true;
     902             :     }
     903             :     else
     904             :     {
     905           0 :         firstZeroPage = SerialNextPage(serialControl->headPage);
     906           0 :         isNewPage = SerialPagePrecedesLogically(serialControl->headPage,
     907             :                                                 targetPage);
     908             :     }
     909             : 
     910           0 :     if (!TransactionIdIsValid(serialControl->headXid)
     911           0 :         || TransactionIdFollows(xid, serialControl->headXid))
     912           0 :         serialControl->headXid = xid;
     913           0 :     if (isNewPage)
     914           0 :         serialControl->headPage = targetPage;
     915             : 
     916           0 :     if (isNewPage)
     917             :     {
     918             :         /* Initialize intervening pages; might involve trading locks */
     919             :         for (;;)
     920             :         {
     921           0 :             lock = SimpleLruGetBankLock(SerialSlruCtl, firstZeroPage);
     922           0 :             LWLockAcquire(lock, LW_EXCLUSIVE);
     923           0 :             slotno = SimpleLruZeroPage(SerialSlruCtl, firstZeroPage);
     924           0 :             if (firstZeroPage == targetPage)
     925           0 :                 break;
     926           0 :             firstZeroPage = SerialNextPage(firstZeroPage);
     927           0 :             LWLockRelease(lock);
     928             :         }
     929             :     }
     930             :     else
     931             :     {
     932           0 :         LWLockAcquire(lock, LW_EXCLUSIVE);
     933           0 :         slotno = SimpleLruReadPage(SerialSlruCtl, targetPage, true, xid);
     934             :     }
     935             : 
     936           0 :     SerialValue(slotno, xid) = minConflictCommitSeqNo;
     937           0 :     SerialSlruCtl->shared->page_dirty[slotno] = true;
     938             : 
     939           0 :     LWLockRelease(lock);
     940           0 :     LWLockRelease(SerialControlLock);
     941             : }
     942             : 
     943             : /*
     944             :  * Get the minimum commitSeqNo for any conflict out for the given xid.  For
     945             :  * a transaction which exists but has no conflict out, InvalidSerCommitSeqNo
     946             :  * will be returned.
     947             :  */
     948             : static SerCommitSeqNo
     949          46 : SerialGetMinConflictCommitSeqNo(TransactionId xid)
     950             : {
     951             :     TransactionId headXid;
     952             :     TransactionId tailXid;
     953             :     SerCommitSeqNo val;
     954             :     int         slotno;
     955             : 
     956             :     Assert(TransactionIdIsValid(xid));
     957             : 
     958          46 :     LWLockAcquire(SerialControlLock, LW_SHARED);
     959          46 :     headXid = serialControl->headXid;
     960          46 :     tailXid = serialControl->tailXid;
     961          46 :     LWLockRelease(SerialControlLock);
     962             : 
     963          46 :     if (!TransactionIdIsValid(headXid))
     964          46 :         return 0;
     965             : 
     966             :     Assert(TransactionIdIsValid(tailXid));
     967             : 
     968           0 :     if (TransactionIdPrecedes(xid, tailXid)
     969           0 :         || TransactionIdFollows(xid, headXid))
     970           0 :         return 0;
     971             : 
     972             :     /*
     973             :      * The following function must be called without holding SLRU bank lock,
     974             :      * but will return with that lock held, which must then be released.
     975             :      */
     976           0 :     slotno = SimpleLruReadPage_ReadOnly(SerialSlruCtl,
     977             :                                         SerialPage(xid), xid);
     978           0 :     val = SerialValue(slotno, xid);
     979           0 :     LWLockRelease(SimpleLruGetBankLock(SerialSlruCtl, SerialPage(xid)));
     980           0 :     return val;
     981             : }
     982             : 
     983             : /*
     984             :  * Call this whenever there is a new xmin for active serializable
     985             :  * transactions.  We don't need to keep information on transactions which
     986             :  * precede that.  InvalidTransactionId means none active, so everything in
     987             :  * the SLRU can be discarded.
     988             :  */
     989             : static void
     990        3362 : SerialSetActiveSerXmin(TransactionId xid)
     991             : {
     992        3362 :     LWLockAcquire(SerialControlLock, LW_EXCLUSIVE);
     993             : 
     994             :     /*
     995             :      * When no sxacts are active, nothing overlaps, set the xid values to
     996             :      * invalid to show that there are no valid entries.  Don't clear headPage,
     997             :      * though.  A new xmin might still land on that page, and we don't want to
     998             :      * repeatedly zero out the same page.
     999             :      */
    1000        3362 :     if (!TransactionIdIsValid(xid))
    1001             :     {
    1002        1664 :         serialControl->tailXid = InvalidTransactionId;
    1003        1664 :         serialControl->headXid = InvalidTransactionId;
    1004        1664 :         LWLockRelease(SerialControlLock);
    1005        1664 :         return;
    1006             :     }
    1007             : 
    1008             :     /*
    1009             :      * When we're recovering prepared transactions, the global xmin might move
    1010             :      * backwards depending on the order they're recovered. Normally that's not
    1011             :      * OK, but during recovery no serializable transactions will commit, so
    1012             :      * the SLRU is empty and we can get away with it.
    1013             :      */
    1014        1698 :     if (RecoveryInProgress())
    1015             :     {
    1016             :         Assert(serialControl->headPage < 0);
    1017           0 :         if (!TransactionIdIsValid(serialControl->tailXid)
    1018           0 :             || TransactionIdPrecedes(xid, serialControl->tailXid))
    1019             :         {
    1020           0 :             serialControl->tailXid = xid;
    1021             :         }
    1022           0 :         LWLockRelease(SerialControlLock);
    1023           0 :         return;
    1024             :     }
    1025             : 
    1026             :     Assert(!TransactionIdIsValid(serialControl->tailXid)
    1027             :            || TransactionIdFollows(xid, serialControl->tailXid));
    1028             : 
    1029        1698 :     serialControl->tailXid = xid;
    1030             : 
    1031        1698 :     LWLockRelease(SerialControlLock);
    1032             : }
    1033             : 
    1034             : /*
    1035             :  * Perform a checkpoint --- either during shutdown, or on-the-fly
    1036             :  *
    1037             :  * We don't have any data that needs to survive a restart, but this is a
    1038             :  * convenient place to truncate the SLRU.
    1039             :  */
    1040             : void
    1041        3316 : CheckPointPredicate(void)
    1042             : {
    1043             :     int64       truncateCutoffPage;
    1044             : 
    1045        3316 :     LWLockAcquire(SerialControlLock, LW_EXCLUSIVE);
    1046             : 
    1047             :     /* Exit quickly if the SLRU is currently not in use. */
    1048        3316 :     if (serialControl->headPage < 0)
    1049             :     {
    1050        3316 :         LWLockRelease(SerialControlLock);
    1051        3316 :         return;
    1052             :     }
    1053             : 
    1054           0 :     if (TransactionIdIsValid(serialControl->tailXid))
    1055             :     {
    1056             :         int64       tailPage;
    1057             : 
    1058           0 :         tailPage = SerialPage(serialControl->tailXid);
    1059             : 
    1060             :         /*
    1061             :          * It is possible for the tailXid to be ahead of the headXid.  This
    1062             :          * occurs if we checkpoint while there are in-progress serializable
    1063             :          * transaction(s) advancing the tail but we are yet to summarize the
    1064             :          * transactions.  In this case, we cutoff up to the headPage and the
    1065             :          * next summary will advance the headXid.
    1066             :          */
    1067           0 :         if (SerialPagePrecedesLogically(tailPage, serialControl->headPage))
    1068             :         {
    1069             :             /* We can truncate the SLRU up to the page containing tailXid */
    1070           0 :             truncateCutoffPage = tailPage;
    1071             :         }
    1072             :         else
    1073           0 :             truncateCutoffPage = serialControl->headPage;
    1074             :     }
    1075             :     else
    1076             :     {
    1077             :         /*----------
    1078             :          * The SLRU is no longer needed. Truncate to head before we set head
    1079             :          * invalid.
    1080             :          *
    1081             :          * XXX: It's possible that the SLRU is not needed again until XID
    1082             :          * wrap-around has happened, so that the segment containing headPage
    1083             :          * that we leave behind will appear to be new again. In that case it
    1084             :          * won't be removed until XID horizon advances enough to make it
    1085             :          * current again.
    1086             :          *
    1087             :          * XXX: This should happen in vac_truncate_clog(), not in checkpoints.
    1088             :          * Consider this scenario, starting from a system with no in-progress
    1089             :          * transactions and VACUUM FREEZE having maximized oldestXact:
    1090             :          * - Start a SERIALIZABLE transaction.
    1091             :          * - Start, finish, and summarize a SERIALIZABLE transaction, creating
    1092             :          *   one SLRU page.
    1093             :          * - Consume XIDs to reach xidStopLimit.
    1094             :          * - Finish all transactions.  Due to the long-running SERIALIZABLE
    1095             :          *   transaction, earlier checkpoints did not touch headPage.  The
    1096             :          *   next checkpoint will change it, but that checkpoint happens after
    1097             :          *   the end of the scenario.
    1098             :          * - VACUUM to advance XID limits.
    1099             :          * - Consume ~2M XIDs, crossing the former xidWrapLimit.
    1100             :          * - Start, finish, and summarize a SERIALIZABLE transaction.
    1101             :          *   SerialAdd() declines to create the targetPage, because headPage
    1102             :          *   is not regarded as in the past relative to that targetPage.  The
    1103             :          *   transaction instigating the summarize fails in
    1104             :          *   SimpleLruReadPage().
    1105             :          */
    1106           0 :         truncateCutoffPage = serialControl->headPage;
    1107           0 :         serialControl->headPage = -1;
    1108             :     }
    1109             : 
    1110           0 :     LWLockRelease(SerialControlLock);
    1111             : 
    1112             :     /*
    1113             :      * Truncate away pages that are no longer required.  Note that no
    1114             :      * additional locking is required, because this is only called as part of
    1115             :      * a checkpoint, and the validity limits have already been determined.
    1116             :      */
    1117           0 :     SimpleLruTruncate(SerialSlruCtl, truncateCutoffPage);
    1118             : 
    1119             :     /*
    1120             :      * Write dirty SLRU pages to disk
    1121             :      *
    1122             :      * This is not actually necessary from a correctness point of view. We do
    1123             :      * it merely as a debugging aid.
    1124             :      *
    1125             :      * We're doing this after the truncation to avoid writing pages right
    1126             :      * before deleting the file in which they sit, which would be completely
    1127             :      * pointless.
    1128             :      */
    1129           0 :     SimpleLruWriteAll(SerialSlruCtl, true);
    1130             : }
    1131             : 
    1132             : /*------------------------------------------------------------------------*/
    1133             : 
    1134             : /*
    1135             :  * PredicateLockShmemInit -- Initialize the predicate locking data structures.
    1136             :  *
    1137             :  * This is called from CreateSharedMemoryAndSemaphores(), which see for
    1138             :  * more comments.  In the normal postmaster case, the shared hash tables
    1139             :  * are created here.  Backends inherit the pointers
    1140             :  * to the shared tables via fork().  In the EXEC_BACKEND case, each
    1141             :  * backend re-executes this code to obtain pointers to the already existing
    1142             :  * shared hash tables.
    1143             :  */
    1144             : void
    1145        2100 : PredicateLockShmemInit(void)
    1146             : {
    1147             :     HASHCTL     info;
    1148             :     long        max_table_size;
    1149             :     Size        requestSize;
    1150             :     bool        found;
    1151             : 
    1152             : #ifndef EXEC_BACKEND
    1153             :     Assert(!IsUnderPostmaster);
    1154             : #endif
    1155             : 
    1156             :     /*
    1157             :      * Compute size of predicate lock target hashtable. Note these
    1158             :      * calculations must agree with PredicateLockShmemSize!
    1159             :      */
    1160        2100 :     max_table_size = NPREDICATELOCKTARGETENTS();
    1161             : 
    1162             :     /*
    1163             :      * Allocate hash table for PREDICATELOCKTARGET structs.  This stores
    1164             :      * per-predicate-lock-target information.
    1165             :      */
    1166        2100 :     info.keysize = sizeof(PREDICATELOCKTARGETTAG);
    1167        2100 :     info.entrysize = sizeof(PREDICATELOCKTARGET);
    1168        2100 :     info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
    1169             : 
    1170        2100 :     PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash",
    1171             :                                             max_table_size,
    1172             :                                             max_table_size,
    1173             :                                             &info,
    1174             :                                             HASH_ELEM | HASH_BLOBS |
    1175             :                                             HASH_PARTITION | HASH_FIXED_SIZE);
    1176             : 
    1177             :     /*
    1178             :      * Reserve a dummy entry in the hash table; we use it to make sure there's
    1179             :      * always one entry available when we need to split or combine a page,
    1180             :      * because running out of space there could mean aborting a
    1181             :      * non-serializable transaction.
    1182             :      */
    1183        2100 :     if (!IsUnderPostmaster)
    1184             :     {
    1185        2100 :         (void) hash_search(PredicateLockTargetHash, &ScratchTargetTag,
    1186             :                            HASH_ENTER, &found);
    1187             :         Assert(!found);
    1188             :     }
    1189             : 
    1190             :     /* Pre-calculate the hash and partition lock of the scratch entry */
    1191        2100 :     ScratchTargetTagHash = PredicateLockTargetTagHashCode(&ScratchTargetTag);
    1192        2100 :     ScratchPartitionLock = PredicateLockHashPartitionLock(ScratchTargetTagHash);
    1193             : 
    1194             :     /*
    1195             :      * Allocate hash table for PREDICATELOCK structs.  This stores per
    1196             :      * xact-lock-of-a-target information.
    1197             :      */
    1198        2100 :     info.keysize = sizeof(PREDICATELOCKTAG);
    1199        2100 :     info.entrysize = sizeof(PREDICATELOCK);
    1200        2100 :     info.hash = predicatelock_hash;
    1201        2100 :     info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
    1202             : 
    1203             :     /* Assume an average of 2 xacts per target */
    1204        2100 :     max_table_size *= 2;
    1205             : 
    1206        2100 :     PredicateLockHash = ShmemInitHash("PREDICATELOCK hash",
    1207             :                                       max_table_size,
    1208             :                                       max_table_size,
    1209             :                                       &info,
    1210             :                                       HASH_ELEM | HASH_FUNCTION |
    1211             :                                       HASH_PARTITION | HASH_FIXED_SIZE);
    1212             : 
    1213             :     /*
    1214             :      * Compute size for serializable transaction hashtable. Note these
    1215             :      * calculations must agree with PredicateLockShmemSize!
    1216             :      */
    1217        2100 :     max_table_size = (MaxBackends + max_prepared_xacts);
    1218             : 
    1219             :     /*
    1220             :      * Allocate a list to hold information on transactions participating in
    1221             :      * predicate locking.
    1222             :      *
    1223             :      * Assume an average of 10 predicate locking transactions per backend.
    1224             :      * This allows aggressive cleanup while detail is present before data must
    1225             :      * be summarized for storage in SLRU and the "dummy" transaction.
    1226             :      */
    1227        2100 :     max_table_size *= 10;
    1228             : 
    1229        2100 :     requestSize = add_size(PredXactListDataSize,
    1230             :                            (mul_size((Size) max_table_size,
    1231             :                                      sizeof(SERIALIZABLEXACT))));
    1232             : 
    1233        2100 :     PredXact = ShmemInitStruct("PredXactList",
    1234             :                                requestSize,
    1235             :                                &found);
    1236             :     Assert(found == IsUnderPostmaster);
    1237        2100 :     if (!found)
    1238             :     {
    1239             :         int         i;
    1240             : 
    1241             :         /* clean everything, both the header and the element */
    1242        2100 :         memset(PredXact, 0, requestSize);
    1243             : 
    1244        2100 :         dlist_init(&PredXact->availableList);
    1245        2100 :         dlist_init(&PredXact->activeList);
    1246        2100 :         PredXact->SxactGlobalXmin = InvalidTransactionId;
    1247        2100 :         PredXact->SxactGlobalXminCount = 0;
    1248        2100 :         PredXact->WritableSxactCount = 0;
    1249        2100 :         PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1;
    1250        2100 :         PredXact->CanPartialClearThrough = 0;
    1251        2100 :         PredXact->HavePartialClearedThrough = 0;
    1252        2100 :         PredXact->element
    1253        2100 :             = (SERIALIZABLEXACT *) ((char *) PredXact + PredXactListDataSize);
    1254             :         /* Add all elements to available list, clean. */
    1255     1994740 :         for (i = 0; i < max_table_size; i++)
    1256             :         {
    1257     1992640 :             LWLockInitialize(&PredXact->element[i].perXactPredicateListLock,
    1258             :                              LWTRANCHE_PER_XACT_PREDICATE_LIST);
    1259     1992640 :             dlist_push_tail(&PredXact->availableList, &PredXact->element[i].xactLink);
    1260             :         }
    1261        2100 :         PredXact->OldCommittedSxact = CreatePredXact();
    1262        2100 :         SetInvalidVirtualTransactionId(PredXact->OldCommittedSxact->vxid);
    1263        2100 :         PredXact->OldCommittedSxact->prepareSeqNo = 0;
    1264        2100 :         PredXact->OldCommittedSxact->commitSeqNo = 0;
    1265        2100 :         PredXact->OldCommittedSxact->SeqNo.lastCommitBeforeSnapshot = 0;
    1266        2100 :         dlist_init(&PredXact->OldCommittedSxact->outConflicts);
    1267        2100 :         dlist_init(&PredXact->OldCommittedSxact->inConflicts);
    1268        2100 :         dlist_init(&PredXact->OldCommittedSxact->predicateLocks);
    1269        2100 :         dlist_node_init(&PredXact->OldCommittedSxact->finishedLink);
    1270        2100 :         dlist_init(&PredXact->OldCommittedSxact->possibleUnsafeConflicts);
    1271        2100 :         PredXact->OldCommittedSxact->topXid = InvalidTransactionId;
    1272        2100 :         PredXact->OldCommittedSxact->finishedBefore = InvalidTransactionId;
    1273        2100 :         PredXact->OldCommittedSxact->xmin = InvalidTransactionId;
    1274        2100 :         PredXact->OldCommittedSxact->flags = SXACT_FLAG_COMMITTED;
    1275        2100 :         PredXact->OldCommittedSxact->pid = 0;
    1276        2100 :         PredXact->OldCommittedSxact->pgprocno = INVALID_PROC_NUMBER;
    1277             :     }
    1278             :     /* This never changes, so let's keep a local copy. */
    1279        2100 :     OldCommittedSxact = PredXact->OldCommittedSxact;
    1280             : 
    1281             :     /*
    1282             :      * Allocate hash table for SERIALIZABLEXID structs.  This stores per-xid
    1283             :      * information for serializable transactions which have accessed data.
    1284             :      */
    1285        2100 :     info.keysize = sizeof(SERIALIZABLEXIDTAG);
    1286        2100 :     info.entrysize = sizeof(SERIALIZABLEXID);
    1287             : 
    1288        2100 :     SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash",
    1289             :                                         max_table_size,
    1290             :                                         max_table_size,
    1291             :                                         &info,
    1292             :                                         HASH_ELEM | HASH_BLOBS |
    1293             :                                         HASH_FIXED_SIZE);
    1294             : 
    1295             :     /*
    1296             :      * Allocate space for tracking rw-conflicts in lists attached to the
    1297             :      * transactions.
    1298             :      *
    1299             :      * Assume an average of 5 conflicts per transaction.  Calculations suggest
    1300             :      * that this will prevent resource exhaustion in even the most pessimal
    1301             :      * loads up to max_connections = 200 with all 200 connections pounding the
    1302             :      * database with serializable transactions.  Beyond that, there may be
    1303             :      * occasional transactions canceled when trying to flag conflicts. That's
    1304             :      * probably OK.
    1305             :      */
    1306        2100 :     max_table_size *= 5;
    1307             : 
    1308        2100 :     requestSize = RWConflictPoolHeaderDataSize +
    1309        2100 :         mul_size((Size) max_table_size,
    1310             :                  RWConflictDataSize);
    1311             : 
    1312        2100 :     RWConflictPool = ShmemInitStruct("RWConflictPool",
    1313             :                                      requestSize,
    1314             :                                      &found);
    1315             :     Assert(found == IsUnderPostmaster);
    1316        2100 :     if (!found)
    1317             :     {
    1318             :         int         i;
    1319             : 
    1320             :         /* clean everything, including the elements */
    1321        2100 :         memset(RWConflictPool, 0, requestSize);
    1322             : 
    1323        2100 :         dlist_init(&RWConflictPool->availableList);
    1324        2100 :         RWConflictPool->element = (RWConflict) ((char *) RWConflictPool +
    1325             :                                                 RWConflictPoolHeaderDataSize);
    1326             :         /* Add all elements to available list, clean. */
    1327     9965300 :         for (i = 0; i < max_table_size; i++)
    1328             :         {
    1329     9963200 :             dlist_push_tail(&RWConflictPool->availableList,
    1330     9963200 :                             &RWConflictPool->element[i].outLink);
    1331             :         }
    1332             :     }
    1333             : 
    1334             :     /*
    1335             :      * Create or attach to the header for the list of finished serializable
    1336             :      * transactions.
    1337             :      */
    1338        2100 :     FinishedSerializableTransactions = (dlist_head *)
    1339        2100 :         ShmemInitStruct("FinishedSerializableTransactions",
    1340             :                         sizeof(dlist_head),
    1341             :                         &found);
    1342             :     Assert(found == IsUnderPostmaster);
    1343        2100 :     if (!found)
    1344        2100 :         dlist_init(FinishedSerializableTransactions);
    1345             : 
    1346             :     /*
    1347             :      * Initialize the SLRU storage for old committed serializable
    1348             :      * transactions.
    1349             :      */
    1350        2100 :     SerialInit();
    1351        2100 : }
    1352             : 
    1353             : /*
    1354             :  * Estimate shared-memory space used for predicate lock table
    1355             :  */
    1356             : Size
    1357        3906 : PredicateLockShmemSize(void)
    1358             : {
    1359        3906 :     Size        size = 0;
    1360             :     long        max_table_size;
    1361             : 
    1362             :     /* predicate lock target hash table */
    1363        3906 :     max_table_size = NPREDICATELOCKTARGETENTS();
    1364        3906 :     size = add_size(size, hash_estimate_size(max_table_size,
    1365             :                                              sizeof(PREDICATELOCKTARGET)));
    1366             : 
    1367             :     /* predicate lock hash table */
    1368        3906 :     max_table_size *= 2;
    1369        3906 :     size = add_size(size, hash_estimate_size(max_table_size,
    1370             :                                              sizeof(PREDICATELOCK)));
    1371             : 
    1372             :     /*
    1373             :      * Since NPREDICATELOCKTARGETENTS is only an estimate, add 10% safety
    1374             :      * margin.
    1375             :      */
    1376        3906 :     size = add_size(size, size / 10);
    1377             : 
    1378             :     /* transaction list */
    1379        3906 :     max_table_size = MaxBackends + max_prepared_xacts;
    1380        3906 :     max_table_size *= 10;
    1381        3906 :     size = add_size(size, PredXactListDataSize);
    1382        3906 :     size = add_size(size, mul_size((Size) max_table_size,
    1383             :                                    sizeof(SERIALIZABLEXACT)));
    1384             : 
    1385             :     /* transaction xid table */
    1386        3906 :     size = add_size(size, hash_estimate_size(max_table_size,
    1387             :                                              sizeof(SERIALIZABLEXID)));
    1388             : 
    1389             :     /* rw-conflict pool */
    1390        3906 :     max_table_size *= 5;
    1391        3906 :     size = add_size(size, RWConflictPoolHeaderDataSize);
    1392        3906 :     size = add_size(size, mul_size((Size) max_table_size,
    1393             :                                    RWConflictDataSize));
    1394             : 
    1395             :     /* Head for list of finished serializable transactions. */
    1396        3906 :     size = add_size(size, sizeof(dlist_head));
    1397             : 
    1398             :     /* Shared memory structures for SLRU tracking of old committed xids. */
    1399        3906 :     size = add_size(size, sizeof(SerialControlData));
    1400        3906 :     size = add_size(size, SimpleLruShmemSize(serializable_buffers, 0));
    1401             : 
    1402        3906 :     return size;
    1403             : }
    1404             : 
    1405             : 
    1406             : /*
    1407             :  * Compute the hash code associated with a PREDICATELOCKTAG.
    1408             :  *
    1409             :  * Because we want to use just one set of partition locks for both the
    1410             :  * PREDICATELOCKTARGET and PREDICATELOCK hash tables, we have to make sure
    1411             :  * that PREDICATELOCKs fall into the same partition number as their
    1412             :  * associated PREDICATELOCKTARGETs.  dynahash.c expects the partition number
    1413             :  * to be the low-order bits of the hash code, and therefore a
    1414             :  * PREDICATELOCKTAG's hash code must have the same low-order bits as the
    1415             :  * associated PREDICATELOCKTARGETTAG's hash code.  We achieve this with this
    1416             :  * specialized hash function.
    1417             :  */
    1418             : static uint32
    1419           0 : predicatelock_hash(const void *key, Size keysize)
    1420             : {
    1421           0 :     const PREDICATELOCKTAG *predicatelocktag = (const PREDICATELOCKTAG *) key;
    1422             :     uint32      targethash;
    1423             : 
    1424             :     Assert(keysize == sizeof(PREDICATELOCKTAG));
    1425             : 
    1426             :     /* Look into the associated target object, and compute its hash code */
    1427           0 :     targethash = PredicateLockTargetTagHashCode(&predicatelocktag->myTarget->tag);
    1428             : 
    1429           0 :     return PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash);
    1430             : }
    1431             : 
    1432             : 
    1433             : /*
    1434             :  * GetPredicateLockStatusData
    1435             :  *      Return a table containing the internal state of the predicate
    1436             :  *      lock manager for use in pg_lock_status.
    1437             :  *
    1438             :  * Like GetLockStatusData, this function tries to hold the partition LWLocks
    1439             :  * for as short a time as possible by returning two arrays that simply
    1440             :  * contain the PREDICATELOCKTARGETTAG and SERIALIZABLEXACT for each lock
    1441             :  * table entry. Multiple copies of the same PREDICATELOCKTARGETTAG and
    1442             :  * SERIALIZABLEXACT will likely appear.
    1443             :  */
    1444             : PredicateLockData *
    1445         462 : GetPredicateLockStatusData(void)
    1446             : {
    1447             :     PredicateLockData *data;
    1448             :     int         i;
    1449             :     int         els,
    1450             :                 el;
    1451             :     HASH_SEQ_STATUS seqstat;
    1452             :     PREDICATELOCK *predlock;
    1453             : 
    1454         462 :     data = (PredicateLockData *) palloc(sizeof(PredicateLockData));
    1455             : 
    1456             :     /*
    1457             :      * To ensure consistency, take simultaneous locks on all partition locks
    1458             :      * in ascending order, then SerializableXactHashLock.
    1459             :      */
    1460        7854 :     for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
    1461        7392 :         LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_SHARED);
    1462         462 :     LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    1463             : 
    1464             :     /* Get number of locks and allocate appropriately-sized arrays. */
    1465         462 :     els = hash_get_num_entries(PredicateLockHash);
    1466         462 :     data->nelements = els;
    1467         462 :     data->locktags = (PREDICATELOCKTARGETTAG *)
    1468         462 :         palloc(sizeof(PREDICATELOCKTARGETTAG) * els);
    1469         462 :     data->xacts = (SERIALIZABLEXACT *)
    1470         462 :         palloc(sizeof(SERIALIZABLEXACT) * els);
    1471             : 
    1472             : 
    1473             :     /* Scan through PredicateLockHash and copy contents */
    1474         462 :     hash_seq_init(&seqstat, PredicateLockHash);
    1475             : 
    1476         462 :     el = 0;
    1477             : 
    1478         468 :     while ((predlock = (PREDICATELOCK *) hash_seq_search(&seqstat)))
    1479             :     {
    1480           6 :         data->locktags[el] = predlock->tag.myTarget->tag;
    1481           6 :         data->xacts[el] = *predlock->tag.myXact;
    1482           6 :         el++;
    1483             :     }
    1484             : 
    1485             :     Assert(el == els);
    1486             : 
    1487             :     /* Release locks in reverse order */
    1488         462 :     LWLockRelease(SerializableXactHashLock);
    1489        7854 :     for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
    1490        7392 :         LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
    1491             : 
    1492         462 :     return data;
    1493             : }
    1494             : 
    1495             : /*
    1496             :  * Free up shared memory structures by pushing the oldest sxact (the one at
    1497             :  * the front of the SummarizeOldestCommittedSxact queue) into summary form.
    1498             :  * Each call will free exactly one SERIALIZABLEXACT structure and may also
    1499             :  * free one or more of these structures: SERIALIZABLEXID, PREDICATELOCK,
    1500             :  * PREDICATELOCKTARGET, RWConflictData.
    1501             :  */
    1502             : static void
    1503           0 : SummarizeOldestCommittedSxact(void)
    1504             : {
    1505             :     SERIALIZABLEXACT *sxact;
    1506             : 
    1507           0 :     LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
    1508             : 
    1509             :     /*
    1510             :      * This function is only called if there are no sxact slots available.
    1511             :      * Some of them must belong to old, already-finished transactions, so
    1512             :      * there should be something in FinishedSerializableTransactions list that
    1513             :      * we can summarize. However, there's a race condition: while we were not
    1514             :      * holding any locks, a transaction might have ended and cleaned up all
    1515             :      * the finished sxact entries already, freeing up their sxact slots. In
    1516             :      * that case, we have nothing to do here. The caller will find one of the
    1517             :      * slots released by the other backend when it retries.
    1518             :      */
    1519           0 :     if (dlist_is_empty(FinishedSerializableTransactions))
    1520             :     {
    1521           0 :         LWLockRelease(SerializableFinishedListLock);
    1522           0 :         return;
    1523             :     }
    1524             : 
    1525             :     /*
    1526             :      * Grab the first sxact off the finished list -- this will be the earliest
    1527             :      * commit.  Remove it from the list.
    1528             :      */
    1529           0 :     sxact = dlist_head_element(SERIALIZABLEXACT, finishedLink,
    1530             :                                FinishedSerializableTransactions);
    1531           0 :     dlist_delete_thoroughly(&sxact->finishedLink);
    1532             : 
    1533             :     /* Add to SLRU summary information. */
    1534           0 :     if (TransactionIdIsValid(sxact->topXid) && !SxactIsReadOnly(sxact))
    1535           0 :         SerialAdd(sxact->topXid, SxactHasConflictOut(sxact)
    1536             :                   ? sxact->SeqNo.earliestOutConflictCommit : InvalidSerCommitSeqNo);
    1537             : 
    1538             :     /* Summarize and release the detail. */
    1539           0 :     ReleaseOneSerializableXact(sxact, false, true);
    1540             : 
    1541           0 :     LWLockRelease(SerializableFinishedListLock);
    1542             : }
    1543             : 
    1544             : /*
    1545             :  * GetSafeSnapshot
    1546             :  *      Obtain and register a snapshot for a READ ONLY DEFERRABLE
    1547             :  *      transaction. Ensures that the snapshot is "safe", i.e. a
    1548             :  *      read-only transaction running on it can execute serializably
    1549             :  *      without further checks. This requires waiting for concurrent
    1550             :  *      transactions to complete, and retrying with a new snapshot if
    1551             :  *      one of them could possibly create a conflict.
    1552             :  *
    1553             :  *      As with GetSerializableTransactionSnapshot (which this is a subroutine
    1554             :  *      for), the passed-in Snapshot pointer should reference a static data
    1555             :  *      area that can safely be passed to GetSnapshotData.
    1556             :  */
    1557             : static Snapshot
    1558          10 : GetSafeSnapshot(Snapshot origSnapshot)
    1559             : {
    1560             :     Snapshot    snapshot;
    1561             : 
    1562             :     Assert(XactReadOnly && XactDeferrable);
    1563             : 
    1564             :     while (true)
    1565             :     {
    1566             :         /*
    1567             :          * GetSerializableTransactionSnapshotInt is going to call
    1568             :          * GetSnapshotData, so we need to provide it the static snapshot area
    1569             :          * our caller passed to us.  The pointer returned is actually the same
    1570             :          * one passed to it, but we avoid assuming that here.
    1571             :          */
    1572          10 :         snapshot = GetSerializableTransactionSnapshotInt(origSnapshot,
    1573             :                                                          NULL, InvalidPid);
    1574             : 
    1575          10 :         if (MySerializableXact == InvalidSerializableXact)
    1576           8 :             return snapshot;    /* no concurrent r/w xacts; it's safe */
    1577             : 
    1578           2 :         LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    1579             : 
    1580             :         /*
    1581             :          * Wait for concurrent transactions to finish. Stop early if one of
    1582             :          * them marked us as conflicted.
    1583             :          */
    1584           2 :         MySerializableXact->flags |= SXACT_FLAG_DEFERRABLE_WAITING;
    1585           4 :         while (!(dlist_is_empty(&MySerializableXact->possibleUnsafeConflicts) ||
    1586           2 :                  SxactIsROUnsafe(MySerializableXact)))
    1587             :         {
    1588           2 :             LWLockRelease(SerializableXactHashLock);
    1589           2 :             ProcWaitForSignal(WAIT_EVENT_SAFE_SNAPSHOT);
    1590           2 :             LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    1591             :         }
    1592           2 :         MySerializableXact->flags &= ~SXACT_FLAG_DEFERRABLE_WAITING;
    1593             : 
    1594           2 :         if (!SxactIsROUnsafe(MySerializableXact))
    1595             :         {
    1596           0 :             LWLockRelease(SerializableXactHashLock);
    1597           0 :             break;              /* success */
    1598             :         }
    1599             : 
    1600           2 :         LWLockRelease(SerializableXactHashLock);
    1601             : 
    1602             :         /* else, need to retry... */
    1603           2 :         ereport(DEBUG2,
    1604             :                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    1605             :                  errmsg_internal("deferrable snapshot was unsafe; trying a new one")));
    1606           2 :         ReleasePredicateLocks(false, false);
    1607             :     }
    1608             : 
    1609             :     /*
    1610             :      * Now we have a safe snapshot, so we don't need to do any further checks.
    1611             :      */
    1612             :     Assert(SxactIsROSafe(MySerializableXact));
    1613           0 :     ReleasePredicateLocks(false, true);
    1614             : 
    1615           0 :     return snapshot;
    1616             : }
    1617             : 
    1618             : /*
    1619             :  * GetSafeSnapshotBlockingPids
    1620             :  *      If the specified process is currently blocked in GetSafeSnapshot,
    1621             :  *      write the process IDs of all processes that it is blocked by
    1622             :  *      into the caller-supplied buffer output[].  The list is truncated at
    1623             :  *      output_size, and the number of PIDs written into the buffer is
    1624             :  *      returned.  Returns zero if the given PID is not currently blocked
    1625             :  *      in GetSafeSnapshot.
    1626             :  */
    1627             : int
    1628        1090 : GetSafeSnapshotBlockingPids(int blocked_pid, int *output, int output_size)
    1629             : {
    1630        1090 :     int         num_written = 0;
    1631             :     dlist_iter  iter;
    1632        1090 :     SERIALIZABLEXACT *blocking_sxact = NULL;
    1633             : 
    1634        1090 :     LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    1635             : 
    1636             :     /* Find blocked_pid's SERIALIZABLEXACT by linear search. */
    1637        2700 :     dlist_foreach(iter, &PredXact->activeList)
    1638             :     {
    1639        1922 :         SERIALIZABLEXACT *sxact =
    1640        1922 :             dlist_container(SERIALIZABLEXACT, xactLink, iter.cur);
    1641             : 
    1642        1922 :         if (sxact->pid == blocked_pid)
    1643             :         {
    1644         312 :             blocking_sxact = sxact;
    1645         312 :             break;
    1646             :         }
    1647             :     }
    1648             : 
    1649             :     /* Did we find it, and is it currently waiting in GetSafeSnapshot? */
    1650        1090 :     if (blocking_sxact != NULL && SxactIsDeferrableWaiting(blocking_sxact))
    1651             :     {
    1652             :         /* Traverse the list of possible unsafe conflicts collecting PIDs. */
    1653           4 :         dlist_foreach(iter, &blocking_sxact->possibleUnsafeConflicts)
    1654             :         {
    1655           4 :             RWConflict  possibleUnsafeConflict =
    1656           4 :                 dlist_container(RWConflictData, inLink, iter.cur);
    1657             : 
    1658           4 :             output[num_written++] = possibleUnsafeConflict->sxactOut->pid;
    1659             : 
    1660           4 :             if (num_written >= output_size)
    1661           4 :                 break;
    1662             :         }
    1663             :     }
    1664             : 
    1665        1090 :     LWLockRelease(SerializableXactHashLock);
    1666             : 
    1667        1090 :     return num_written;
    1668             : }
    1669             : 
    1670             : /*
    1671             :  * Acquire a snapshot that can be used for the current transaction.
    1672             :  *
    1673             :  * Make sure we have a SERIALIZABLEXACT reference in MySerializableXact.
    1674             :  * It should be current for this process and be contained in PredXact.
    1675             :  *
    1676             :  * The passed-in Snapshot pointer should reference a static data area that
    1677             :  * can safely be passed to GetSnapshotData.  The return value is actually
    1678             :  * always this same pointer; no new snapshot data structure is allocated
    1679             :  * within this function.
    1680             :  */
    1681             : Snapshot
    1682        3280 : GetSerializableTransactionSnapshot(Snapshot snapshot)
    1683             : {
    1684             :     Assert(IsolationIsSerializable());
    1685             : 
    1686             :     /*
    1687             :      * Can't use serializable mode while recovery is still active, as it is,
    1688             :      * for example, on a hot standby.  We could get here despite the check in
    1689             :      * check_transaction_isolation() if default_transaction_isolation is set
    1690             :      * to serializable, so phrase the hint accordingly.
    1691             :      */
    1692        3280 :     if (RecoveryInProgress())
    1693           0 :         ereport(ERROR,
    1694             :                 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
    1695             :                  errmsg("cannot use serializable mode in a hot standby"),
    1696             :                  errdetail("\"default_transaction_isolation\" is set to \"serializable\"."),
    1697             :                  errhint("You can use \"SET default_transaction_isolation = 'repeatable read'\" to change the default.")));
    1698             : 
    1699             :     /*
    1700             :      * A special optimization is available for SERIALIZABLE READ ONLY
    1701             :      * DEFERRABLE transactions -- we can wait for a suitable snapshot and
    1702             :      * thereby avoid all SSI overhead once it's running.
    1703             :      */
    1704        3280 :     if (XactReadOnly && XactDeferrable)
    1705           8 :         return GetSafeSnapshot(snapshot);
    1706             : 
    1707        3272 :     return GetSerializableTransactionSnapshotInt(snapshot,
    1708             :                                                  NULL, InvalidPid);
    1709             : }
    1710             : 
    1711             : /*
    1712             :  * Import a snapshot to be used for the current transaction.
    1713             :  *
    1714             :  * This is nearly the same as GetSerializableTransactionSnapshot, except that
    1715             :  * we don't take a new snapshot, but rather use the data we're handed.
    1716             :  *
    1717             :  * The caller must have verified that the snapshot came from a serializable
    1718             :  * transaction; and if we're read-write, the source transaction must not be
    1719             :  * read-only.
    1720             :  */
    1721             : void
    1722          26 : SetSerializableTransactionSnapshot(Snapshot snapshot,
    1723             :                                    VirtualTransactionId *sourcevxid,
    1724             :                                    int sourcepid)
    1725             : {
    1726             :     Assert(IsolationIsSerializable());
    1727             : 
    1728             :     /*
    1729             :      * If this is called by parallel.c in a parallel worker, we don't want to
    1730             :      * create a SERIALIZABLEXACT just yet because the leader's
    1731             :      * SERIALIZABLEXACT will be installed with AttachSerializableXact().  We
    1732             :      * also don't want to reject SERIALIZABLE READ ONLY DEFERRABLE in this
    1733             :      * case, because the leader has already determined that the snapshot it
    1734             :      * has passed us is safe.  So there is nothing for us to do.
    1735             :      */
    1736          26 :     if (IsParallelWorker())
    1737          26 :         return;
    1738             : 
    1739             :     /*
    1740             :      * We do not allow SERIALIZABLE READ ONLY DEFERRABLE transactions to
    1741             :      * import snapshots, since there's no way to wait for a safe snapshot when
    1742             :      * we're using the snap we're told to.  (XXX instead of throwing an error,
    1743             :      * we could just ignore the XactDeferrable flag?)
    1744             :      */
    1745           0 :     if (XactReadOnly && XactDeferrable)
    1746           0 :         ereport(ERROR,
    1747             :                 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
    1748             :                  errmsg("a snapshot-importing transaction must not be READ ONLY DEFERRABLE")));
    1749             : 
    1750           0 :     (void) GetSerializableTransactionSnapshotInt(snapshot, sourcevxid,
    1751             :                                                  sourcepid);
    1752             : }
    1753             : 
    1754             : /*
    1755             :  * Guts of GetSerializableTransactionSnapshot
    1756             :  *
    1757             :  * If sourcevxid is valid, this is actually an import operation and we should
    1758             :  * skip calling GetSnapshotData, because the snapshot contents are already
    1759             :  * loaded up.  HOWEVER: to avoid race conditions, we must check that the
    1760             :  * source xact is still running after we acquire SerializableXactHashLock.
    1761             :  * We do that by calling ProcArrayInstallImportedXmin.
    1762             :  */
    1763             : static Snapshot
    1764        3282 : GetSerializableTransactionSnapshotInt(Snapshot snapshot,
    1765             :                                       VirtualTransactionId *sourcevxid,
    1766             :                                       int sourcepid)
    1767             : {
    1768             :     PGPROC     *proc;
    1769             :     VirtualTransactionId vxid;
    1770             :     SERIALIZABLEXACT *sxact,
    1771             :                *othersxact;
    1772             : 
    1773             :     /* We only do this for serializable transactions.  Once. */
    1774             :     Assert(MySerializableXact == InvalidSerializableXact);
    1775             : 
    1776             :     Assert(!RecoveryInProgress());
    1777             : 
    1778             :     /*
    1779             :      * Since all parts of a serializable transaction must use the same
    1780             :      * snapshot, it is too late to establish one after a parallel operation
    1781             :      * has begun.
    1782             :      */
    1783        3282 :     if (IsInParallelMode())
    1784           0 :         elog(ERROR, "cannot establish serializable snapshot during a parallel operation");
    1785             : 
    1786        3282 :     proc = MyProc;
    1787             :     Assert(proc != NULL);
    1788        3282 :     GET_VXID_FROM_PGPROC(vxid, *proc);
    1789             : 
    1790             :     /*
    1791             :      * First we get the sxact structure, which may involve looping and access
    1792             :      * to the "finished" list to free a structure for use.
    1793             :      *
    1794             :      * We must hold SerializableXactHashLock when taking/checking the snapshot
    1795             :      * to avoid race conditions, for much the same reasons that
    1796             :      * GetSnapshotData takes the ProcArrayLock.  Since we might have to
    1797             :      * release SerializableXactHashLock to call SummarizeOldestCommittedSxact,
    1798             :      * this means we have to create the sxact first, which is a bit annoying
    1799             :      * (in particular, an elog(ERROR) in procarray.c would cause us to leak
    1800             :      * the sxact).  Consider refactoring to avoid this.
    1801             :      */
    1802             : #ifdef TEST_SUMMARIZE_SERIAL
    1803             :     SummarizeOldestCommittedSxact();
    1804             : #endif
    1805        3282 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    1806             :     do
    1807             :     {
    1808        3282 :         sxact = CreatePredXact();
    1809             :         /* If null, push out committed sxact to SLRU summary & retry. */
    1810        3282 :         if (!sxact)
    1811             :         {
    1812           0 :             LWLockRelease(SerializableXactHashLock);
    1813           0 :             SummarizeOldestCommittedSxact();
    1814           0 :             LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    1815             :         }
    1816        3282 :     } while (!sxact);
    1817             : 
    1818             :     /* Get the snapshot, or check that it's safe to use */
    1819        3282 :     if (!sourcevxid)
    1820        3282 :         snapshot = GetSnapshotData(snapshot);
    1821           0 :     else if (!ProcArrayInstallImportedXmin(snapshot->xmin, sourcevxid))
    1822             :     {
    1823           0 :         ReleasePredXact(sxact);
    1824           0 :         LWLockRelease(SerializableXactHashLock);
    1825           0 :         ereport(ERROR,
    1826             :                 (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    1827             :                  errmsg("could not import the requested snapshot"),
    1828             :                  errdetail("The source process with PID %d is not running anymore.",
    1829             :                            sourcepid)));
    1830             :     }
    1831             : 
    1832             :     /*
    1833             :      * If there are no serializable transactions which are not read-only, we
    1834             :      * can "opt out" of predicate locking and conflict checking for a
    1835             :      * read-only transaction.
    1836             :      *
    1837             :      * The reason this is safe is that a read-only transaction can only become
    1838             :      * part of a dangerous structure if it overlaps a writable transaction
    1839             :      * which in turn overlaps a writable transaction which committed before
    1840             :      * the read-only transaction started.  A new writable transaction can
    1841             :      * overlap this one, but it can't meet the other condition of overlapping
    1842             :      * a transaction which committed before this one started.
    1843             :      */
    1844        3282 :     if (XactReadOnly && PredXact->WritableSxactCount == 0)
    1845             :     {
    1846         224 :         ReleasePredXact(sxact);
    1847         224 :         LWLockRelease(SerializableXactHashLock);
    1848         224 :         return snapshot;
    1849             :     }
    1850             : 
    1851             :     /* Initialize the structure. */
    1852        3058 :     sxact->vxid = vxid;
    1853        3058 :     sxact->SeqNo.lastCommitBeforeSnapshot = PredXact->LastSxactCommitSeqNo;
    1854        3058 :     sxact->prepareSeqNo = InvalidSerCommitSeqNo;
    1855        3058 :     sxact->commitSeqNo = InvalidSerCommitSeqNo;
    1856        3058 :     dlist_init(&(sxact->outConflicts));
    1857        3058 :     dlist_init(&(sxact->inConflicts));
    1858        3058 :     dlist_init(&(sxact->possibleUnsafeConflicts));
    1859        3058 :     sxact->topXid = GetTopTransactionIdIfAny();
    1860        3058 :     sxact->finishedBefore = InvalidTransactionId;
    1861        3058 :     sxact->xmin = snapshot->xmin;
    1862        3058 :     sxact->pid = MyProcPid;
    1863        3058 :     sxact->pgprocno = MyProcNumber;
    1864        3058 :     dlist_init(&sxact->predicateLocks);
    1865        3058 :     dlist_node_init(&sxact->finishedLink);
    1866        3058 :     sxact->flags = 0;
    1867        3058 :     if (XactReadOnly)
    1868             :     {
    1869             :         dlist_iter  iter;
    1870             : 
    1871         212 :         sxact->flags |= SXACT_FLAG_READ_ONLY;
    1872             : 
    1873             :         /*
    1874             :          * Register all concurrent r/w transactions as possible conflicts; if
    1875             :          * all of them commit without any outgoing conflicts to earlier
    1876             :          * transactions then this snapshot can be deemed safe (and we can run
    1877             :          * without tracking predicate locks).
    1878             :          */
    1879         928 :         dlist_foreach(iter, &PredXact->activeList)
    1880             :         {
    1881         716 :             othersxact = dlist_container(SERIALIZABLEXACT, xactLink, iter.cur);
    1882             : 
    1883         716 :             if (!SxactIsCommitted(othersxact)
    1884         478 :                 && !SxactIsDoomed(othersxact)
    1885         478 :                 && !SxactIsReadOnly(othersxact))
    1886             :             {
    1887         264 :                 SetPossibleUnsafeConflict(sxact, othersxact);
    1888             :             }
    1889             :         }
    1890             : 
    1891             :         /*
    1892             :          * If we didn't find any possibly unsafe conflicts because every
    1893             :          * uncommitted writable transaction turned out to be doomed, then we
    1894             :          * can "opt out" immediately.  See comments above the earlier check
    1895             :          * for PredXact->WritableSxactCount == 0.
    1896             :          */
    1897         212 :         if (dlist_is_empty(&sxact->possibleUnsafeConflicts))
    1898             :         {
    1899           0 :             ReleasePredXact(sxact);
    1900           0 :             LWLockRelease(SerializableXactHashLock);
    1901           0 :             return snapshot;
    1902             :         }
    1903             :     }
    1904             :     else
    1905             :     {
    1906        2846 :         ++(PredXact->WritableSxactCount);
    1907             :         Assert(PredXact->WritableSxactCount <=
    1908             :                (MaxBackends + max_prepared_xacts));
    1909             :     }
    1910             : 
    1911             :     /* Maintain serializable global xmin info. */
    1912        3058 :     if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
    1913             :     {
    1914             :         Assert(PredXact->SxactGlobalXminCount == 0);
    1915        1664 :         PredXact->SxactGlobalXmin = snapshot->xmin;
    1916        1664 :         PredXact->SxactGlobalXminCount = 1;
    1917        1664 :         SerialSetActiveSerXmin(snapshot->xmin);
    1918             :     }
    1919        1394 :     else if (TransactionIdEquals(snapshot->xmin, PredXact->SxactGlobalXmin))
    1920             :     {
    1921             :         Assert(PredXact->SxactGlobalXminCount > 0);
    1922        1326 :         PredXact->SxactGlobalXminCount++;
    1923             :     }
    1924             :     else
    1925             :     {
    1926             :         Assert(TransactionIdFollows(snapshot->xmin, PredXact->SxactGlobalXmin));
    1927             :     }
    1928             : 
    1929        3058 :     MySerializableXact = sxact;
    1930        3058 :     MyXactDidWrite = false;     /* haven't written anything yet */
    1931             : 
    1932        3058 :     LWLockRelease(SerializableXactHashLock);
    1933             : 
    1934        3058 :     CreateLocalPredicateLockHash();
    1935             : 
    1936        3058 :     return snapshot;
    1937             : }
    1938             : 
    1939             : static void
    1940        3084 : CreateLocalPredicateLockHash(void)
    1941             : {
    1942             :     HASHCTL     hash_ctl;
    1943             : 
    1944             :     /* Initialize the backend-local hash table of parent locks */
    1945             :     Assert(LocalPredicateLockHash == NULL);
    1946        3084 :     hash_ctl.keysize = sizeof(PREDICATELOCKTARGETTAG);
    1947        3084 :     hash_ctl.entrysize = sizeof(LOCALPREDICATELOCK);
    1948        3084 :     LocalPredicateLockHash = hash_create("Local predicate lock",
    1949             :                                          max_predicate_locks_per_xact,
    1950             :                                          &hash_ctl,
    1951             :                                          HASH_ELEM | HASH_BLOBS);
    1952        3084 : }
    1953             : 
    1954             : /*
    1955             :  * Register the top level XID in SerializableXidHash.
    1956             :  * Also store it for easy reference in MySerializableXact.
    1957             :  */
    1958             : void
    1959      263994 : RegisterPredicateLockingXid(TransactionId xid)
    1960             : {
    1961             :     SERIALIZABLEXIDTAG sxidtag;
    1962             :     SERIALIZABLEXID *sxid;
    1963             :     bool        found;
    1964             : 
    1965             :     /*
    1966             :      * If we're not tracking predicate lock data for this transaction, we
    1967             :      * should ignore the request and return quickly.
    1968             :      */
    1969      263994 :     if (MySerializableXact == InvalidSerializableXact)
    1970      261468 :         return;
    1971             : 
    1972             :     /* We should have a valid XID and be at the top level. */
    1973             :     Assert(TransactionIdIsValid(xid));
    1974             : 
    1975        2526 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    1976             : 
    1977             :     /* This should only be done once per transaction. */
    1978             :     Assert(MySerializableXact->topXid == InvalidTransactionId);
    1979             : 
    1980        2526 :     MySerializableXact->topXid = xid;
    1981             : 
    1982        2526 :     sxidtag.xid = xid;
    1983        2526 :     sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash,
    1984             :                                            &sxidtag,
    1985             :                                            HASH_ENTER, &found);
    1986             :     Assert(!found);
    1987             : 
    1988             :     /* Initialize the structure. */
    1989        2526 :     sxid->myXact = MySerializableXact;
    1990        2526 :     LWLockRelease(SerializableXactHashLock);
    1991             : }
    1992             : 
    1993             : 
    1994             : /*
    1995             :  * Check whether there are any predicate locks held by any transaction
    1996             :  * for the page at the given block number.
    1997             :  *
    1998             :  * Note that the transaction may be completed but not yet subject to
    1999             :  * cleanup due to overlapping serializable transactions.  This must
    2000             :  * return valid information regardless of transaction isolation level.
    2001             :  *
    2002             :  * Also note that this doesn't check for a conflicting relation lock,
    2003             :  * just a lock specifically on the given page.
    2004             :  *
    2005             :  * One use is to support proper behavior during GiST index vacuum.
    2006             :  */
    2007             : bool
    2008           0 : PageIsPredicateLocked(Relation relation, BlockNumber blkno)
    2009             : {
    2010             :     PREDICATELOCKTARGETTAG targettag;
    2011             :     uint32      targettaghash;
    2012             :     LWLock     *partitionLock;
    2013             :     PREDICATELOCKTARGET *target;
    2014             : 
    2015           0 :     SET_PREDICATELOCKTARGETTAG_PAGE(targettag,
    2016             :                                     relation->rd_locator.dbOid,
    2017             :                                     relation->rd_id,
    2018             :                                     blkno);
    2019             : 
    2020           0 :     targettaghash = PredicateLockTargetTagHashCode(&targettag);
    2021           0 :     partitionLock = PredicateLockHashPartitionLock(targettaghash);
    2022           0 :     LWLockAcquire(partitionLock, LW_SHARED);
    2023             :     target = (PREDICATELOCKTARGET *)
    2024           0 :         hash_search_with_hash_value(PredicateLockTargetHash,
    2025             :                                     &targettag, targettaghash,
    2026             :                                     HASH_FIND, NULL);
    2027           0 :     LWLockRelease(partitionLock);
    2028             : 
    2029           0 :     return (target != NULL);
    2030             : }
    2031             : 
    2032             : 
    2033             : /*
    2034             :  * Check whether a particular lock is held by this transaction.
    2035             :  *
    2036             :  * Important note: this function may return false even if the lock is
    2037             :  * being held, because it uses the local lock table which is not
    2038             :  * updated if another transaction modifies our lock list (e.g. to
    2039             :  * split an index page). It can also return true when a coarser
    2040             :  * granularity lock that covers this target is being held. Be careful
    2041             :  * to only use this function in circumstances where such errors are
    2042             :  * acceptable!
    2043             :  */
    2044             : static bool
    2045      154380 : PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag)
    2046             : {
    2047             :     LOCALPREDICATELOCK *lock;
    2048             : 
    2049             :     /* check local hash table */
    2050      154380 :     lock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash,
    2051             :                                               targettag,
    2052             :                                               HASH_FIND, NULL);
    2053             : 
    2054      154380 :     if (!lock)
    2055       60178 :         return false;
    2056             : 
    2057             :     /*
    2058             :      * Found entry in the table, but still need to check whether it's actually
    2059             :      * held -- it could just be a parent of some held lock.
    2060             :      */
    2061       94202 :     return lock->held;
    2062             : }
    2063             : 
    2064             : /*
    2065             :  * Return the parent lock tag in the lock hierarchy: the next coarser
    2066             :  * lock that covers the provided tag.
    2067             :  *
    2068             :  * Returns true and sets *parent to the parent tag if one exists,
    2069             :  * returns false if none exists.
    2070             :  */
    2071             : static bool
    2072       90298 : GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag,
    2073             :                           PREDICATELOCKTARGETTAG *parent)
    2074             : {
    2075       90298 :     switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag))
    2076             :     {
    2077       19600 :         case PREDLOCKTAG_RELATION:
    2078             :             /* relation locks have no parent lock */
    2079       19600 :             return false;
    2080             : 
    2081       16832 :         case PREDLOCKTAG_PAGE:
    2082             :             /* parent lock is relation lock */
    2083       16832 :             SET_PREDICATELOCKTARGETTAG_RELATION(*parent,
    2084             :                                                 GET_PREDICATELOCKTARGETTAG_DB(*tag),
    2085             :                                                 GET_PREDICATELOCKTARGETTAG_RELATION(*tag));
    2086             : 
    2087       16832 :             return true;
    2088             : 
    2089       53866 :         case PREDLOCKTAG_TUPLE:
    2090             :             /* parent lock is page lock */
    2091       53866 :             SET_PREDICATELOCKTARGETTAG_PAGE(*parent,
    2092             :                                             GET_PREDICATELOCKTARGETTAG_DB(*tag),
    2093             :                                             GET_PREDICATELOCKTARGETTAG_RELATION(*tag),
    2094             :                                             GET_PREDICATELOCKTARGETTAG_PAGE(*tag));
    2095       53866 :             return true;
    2096             :     }
    2097             : 
    2098             :     /* not reachable */
    2099             :     Assert(false);
    2100           0 :     return false;
    2101             : }
    2102             : 
    2103             : /*
    2104             :  * Check whether the lock we are considering is already covered by a
    2105             :  * coarser lock for our transaction.
    2106             :  *
    2107             :  * Like PredicateLockExists, this function might return a false
    2108             :  * negative, but it will never return a false positive.
    2109             :  */
    2110             : static bool
    2111       52062 : CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag)
    2112             : {
    2113             :     PREDICATELOCKTARGETTAG targettag,
    2114             :                 parenttag;
    2115             : 
    2116       52062 :     targettag = *newtargettag;
    2117             : 
    2118             :     /* check parents iteratively until no more */
    2119       62830 :     while (GetParentPredicateLockTag(&targettag, &parenttag))
    2120             :     {
    2121       54410 :         targettag = parenttag;
    2122       54410 :         if (PredicateLockExists(&targettag))
    2123       43642 :             return true;
    2124             :     }
    2125             : 
    2126             :     /* no more parents to check; lock is not covered */
    2127        8420 :     return false;
    2128             : }
    2129             : 
    2130             : /*
    2131             :  * Remove the dummy entry from the predicate lock target hash, to free up some
    2132             :  * scratch space. The caller must be holding SerializablePredicateListLock,
    2133             :  * and must restore the entry with RestoreScratchTarget() before releasing the
    2134             :  * lock.
    2135             :  *
    2136             :  * If lockheld is true, the caller is already holding the partition lock
    2137             :  * of the partition containing the scratch entry.
    2138             :  */
    2139             : static void
    2140          94 : RemoveScratchTarget(bool lockheld)
    2141             : {
    2142             :     bool        found;
    2143             : 
    2144             :     Assert(LWLockHeldByMe(SerializablePredicateListLock));
    2145             : 
    2146          94 :     if (!lockheld)
    2147           0 :         LWLockAcquire(ScratchPartitionLock, LW_EXCLUSIVE);
    2148          94 :     hash_search_with_hash_value(PredicateLockTargetHash,
    2149             :                                 &ScratchTargetTag,
    2150             :                                 ScratchTargetTagHash,
    2151             :                                 HASH_REMOVE, &found);
    2152             :     Assert(found);
    2153          94 :     if (!lockheld)
    2154           0 :         LWLockRelease(ScratchPartitionLock);
    2155          94 : }
    2156             : 
    2157             : /*
    2158             :  * Re-insert the dummy entry in predicate lock target hash.
    2159             :  */
    2160             : static void
    2161          94 : RestoreScratchTarget(bool lockheld)
    2162             : {
    2163             :     bool        found;
    2164             : 
    2165             :     Assert(LWLockHeldByMe(SerializablePredicateListLock));
    2166             : 
    2167          94 :     if (!lockheld)
    2168           0 :         LWLockAcquire(ScratchPartitionLock, LW_EXCLUSIVE);
    2169          94 :     hash_search_with_hash_value(PredicateLockTargetHash,
    2170             :                                 &ScratchTargetTag,
    2171             :                                 ScratchTargetTagHash,
    2172             :                                 HASH_ENTER, &found);
    2173             :     Assert(!found);
    2174          94 :     if (!lockheld)
    2175           0 :         LWLockRelease(ScratchPartitionLock);
    2176          94 : }
    2177             : 
    2178             : /*
    2179             :  * Check whether the list of related predicate locks is empty for a
    2180             :  * predicate lock target, and remove the target if it is.
    2181             :  */
    2182             : static void
    2183        8408 : RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, uint32 targettaghash)
    2184             : {
    2185             :     PREDICATELOCKTARGET *rmtarget PG_USED_FOR_ASSERTS_ONLY;
    2186             : 
    2187             :     Assert(LWLockHeldByMe(SerializablePredicateListLock));
    2188             : 
    2189             :     /* Can't remove it until no locks at this target. */
    2190        8408 :     if (!dlist_is_empty(&target->predicateLocks))
    2191        1922 :         return;
    2192             : 
    2193             :     /* Actually remove the target. */
    2194        6486 :     rmtarget = hash_search_with_hash_value(PredicateLockTargetHash,
    2195        6486 :                                            &target->tag,
    2196             :                                            targettaghash,
    2197             :                                            HASH_REMOVE, NULL);
    2198             :     Assert(rmtarget == target);
    2199             : }
    2200             : 
    2201             : /*
    2202             :  * Delete child target locks owned by this process.
    2203             :  * This implementation is assuming that the usage of each target tag field
    2204             :  * is uniform.  No need to make this hard if we don't have to.
    2205             :  *
    2206             :  * We acquire an LWLock in the case of parallel mode, because worker
    2207             :  * backends have access to the leader's SERIALIZABLEXACT.  Otherwise,
    2208             :  * we aren't acquiring LWLocks for the predicate lock or lock
    2209             :  * target structures associated with this transaction unless we're going
    2210             :  * to modify them, because no other process is permitted to modify our
    2211             :  * locks.
    2212             :  */
    2213             : static void
    2214        4688 : DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag)
    2215             : {
    2216             :     SERIALIZABLEXACT *sxact;
    2217             :     PREDICATELOCK *predlock;
    2218             :     dlist_mutable_iter iter;
    2219             : 
    2220        4688 :     LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    2221        4688 :     sxact = MySerializableXact;
    2222        4688 :     if (IsInParallelMode())
    2223          22 :         LWLockAcquire(&sxact->perXactPredicateListLock, LW_EXCLUSIVE);
    2224             : 
    2225       15532 :     dlist_foreach_modify(iter, &sxact->predicateLocks)
    2226             :     {
    2227             :         PREDICATELOCKTAG oldlocktag;
    2228             :         PREDICATELOCKTARGET *oldtarget;
    2229             :         PREDICATELOCKTARGETTAG oldtargettag;
    2230             : 
    2231       10844 :         predlock = dlist_container(PREDICATELOCK, xactLink, iter.cur);
    2232             : 
    2233       10844 :         oldlocktag = predlock->tag;
    2234             :         Assert(oldlocktag.myXact == sxact);
    2235       10844 :         oldtarget = oldlocktag.myTarget;
    2236       10844 :         oldtargettag = oldtarget->tag;
    2237             : 
    2238       10844 :         if (TargetTagIsCoveredBy(oldtargettag, *newtargettag))
    2239             :         {
    2240             :             uint32      oldtargettaghash;
    2241             :             LWLock     *partitionLock;
    2242             :             PREDICATELOCK *rmpredlock PG_USED_FOR_ASSERTS_ONLY;
    2243             : 
    2244        1998 :             oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag);
    2245        1998 :             partitionLock = PredicateLockHashPartitionLock(oldtargettaghash);
    2246             : 
    2247        1998 :             LWLockAcquire(partitionLock, LW_EXCLUSIVE);
    2248             : 
    2249        1998 :             dlist_delete(&predlock->xactLink);
    2250        1998 :             dlist_delete(&predlock->targetLink);
    2251        1998 :             rmpredlock = hash_search_with_hash_value
    2252             :                 (PredicateLockHash,
    2253             :                  &oldlocktag,
    2254        1998 :                  PredicateLockHashCodeFromTargetHashCode(&oldlocktag,
    2255             :                                                          oldtargettaghash),
    2256             :                  HASH_REMOVE, NULL);
    2257             :             Assert(rmpredlock == predlock);
    2258             : 
    2259        1998 :             RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash);
    2260             : 
    2261        1998 :             LWLockRelease(partitionLock);
    2262             : 
    2263        1998 :             DecrementParentLocks(&oldtargettag);
    2264             :         }
    2265             :     }
    2266        4688 :     if (IsInParallelMode())
    2267          22 :         LWLockRelease(&sxact->perXactPredicateListLock);
    2268        4688 :     LWLockRelease(SerializablePredicateListLock);
    2269        4688 : }
    2270             : 
    2271             : /*
    2272             :  * Returns the promotion limit for a given predicate lock target.  This is the
    2273             :  * max number of descendant locks allowed before promoting to the specified
    2274             :  * tag. Note that the limit includes non-direct descendants (e.g., both tuples
    2275             :  * and pages for a relation lock).
    2276             :  *
    2277             :  * Currently the default limit is 2 for a page lock, and half of the value of
    2278             :  * max_pred_locks_per_transaction - 1 for a relation lock, to match behavior
    2279             :  * of earlier releases when upgrading.
    2280             :  *
    2281             :  * TODO SSI: We should probably add additional GUCs to allow a maximum ratio
    2282             :  * of page and tuple locks based on the pages in a relation, and the maximum
    2283             :  * ratio of tuple locks to tuples in a page.  This would provide more
    2284             :  * generally "balanced" allocation of locks to where they are most useful,
    2285             :  * while still allowing the absolute numbers to prevent one relation from
    2286             :  * tying up all predicate lock resources.
    2287             :  */
    2288             : static int
    2289       10768 : MaxPredicateChildLocks(const PREDICATELOCKTARGETTAG *tag)
    2290             : {
    2291       10768 :     switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag))
    2292             :     {
    2293        7036 :         case PREDLOCKTAG_RELATION:
    2294        7036 :             return max_predicate_locks_per_relation < 0
    2295             :                 ? (max_predicate_locks_per_xact
    2296        7036 :                    / (-max_predicate_locks_per_relation)) - 1
    2297        7036 :                 : max_predicate_locks_per_relation;
    2298             : 
    2299        3732 :         case PREDLOCKTAG_PAGE:
    2300        3732 :             return max_predicate_locks_per_page;
    2301             : 
    2302           0 :         case PREDLOCKTAG_TUPLE:
    2303             : 
    2304             :             /*
    2305             :              * not reachable: nothing is finer-granularity than a tuple, so we
    2306             :              * should never try to promote to it.
    2307             :              */
    2308             :             Assert(false);
    2309           0 :             return 0;
    2310             :     }
    2311             : 
    2312             :     /* not reachable */
    2313             :     Assert(false);
    2314           0 :     return 0;
    2315             : }
    2316             : 
    2317             : /*
    2318             :  * For all ancestors of a newly-acquired predicate lock, increment
    2319             :  * their child count in the parent hash table. If any of them have
    2320             :  * more descendants than their promotion threshold, acquire the
    2321             :  * coarsest such lock.
    2322             :  *
    2323             :  * Returns true if a parent lock was acquired and false otherwise.
    2324             :  */
    2325             : static bool
    2326        8420 : CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag)
    2327             : {
    2328             :     PREDICATELOCKTARGETTAG targettag,
    2329             :                 nexttag,
    2330             :                 promotiontag;
    2331             :     LOCALPREDICATELOCK *parentlock;
    2332             :     bool        found,
    2333             :                 promote;
    2334             : 
    2335        8420 :     promote = false;
    2336             : 
    2337        8420 :     targettag = *reqtag;
    2338             : 
    2339             :     /* check parents iteratively */
    2340       19188 :     while (GetParentPredicateLockTag(&targettag, &nexttag))
    2341             :     {
    2342       10768 :         targettag = nexttag;
    2343       10768 :         parentlock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash,
    2344             :                                                         &targettag,
    2345             :                                                         HASH_ENTER,
    2346             :                                                         &found);
    2347       10768 :         if (!found)
    2348             :         {
    2349        6646 :             parentlock->held = false;
    2350        6646 :             parentlock->childLocks = 1;
    2351             :         }
    2352             :         else
    2353        4122 :             parentlock->childLocks++;
    2354             : 
    2355       10768 :         if (parentlock->childLocks >
    2356       10768 :             MaxPredicateChildLocks(&targettag))
    2357             :         {
    2358             :             /*
    2359             :              * We should promote to this parent lock. Continue to check its
    2360             :              * ancestors, however, both to get their child counts right and to
    2361             :              * check whether we should just go ahead and promote to one of
    2362             :              * them.
    2363             :              */
    2364         666 :             promotiontag = targettag;
    2365         666 :             promote = true;
    2366             :         }
    2367             :     }
    2368             : 
    2369        8420 :     if (promote)
    2370             :     {
    2371             :         /* acquire coarsest ancestor eligible for promotion */
    2372         666 :         PredicateLockAcquire(&promotiontag);
    2373         666 :         return true;
    2374             :     }
    2375             :     else
    2376        7754 :         return false;
    2377             : }
    2378             : 
    2379             : /*
    2380             :  * When releasing a lock, decrement the child count on all ancestor
    2381             :  * locks.
    2382             :  *
    2383             :  * This is called only when releasing a lock via
    2384             :  * DeleteChildTargetLocks (i.e. when a lock becomes redundant because
    2385             :  * we've acquired its parent, possibly due to promotion) or when a new
    2386             :  * MVCC write lock makes the predicate lock unnecessary. There's no
    2387             :  * point in calling it when locks are released at transaction end, as
    2388             :  * this information is no longer needed.
    2389             :  */
    2390             : static void
    2391        2760 : DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag)
    2392             : {
    2393             :     PREDICATELOCKTARGETTAG parenttag,
    2394             :                 nexttag;
    2395             : 
    2396        2760 :     parenttag = *targettag;
    2397             : 
    2398        8280 :     while (GetParentPredicateLockTag(&parenttag, &nexttag))
    2399             :     {
    2400             :         uint32      targettaghash;
    2401             :         LOCALPREDICATELOCK *parentlock,
    2402             :                    *rmlock PG_USED_FOR_ASSERTS_ONLY;
    2403             : 
    2404        5520 :         parenttag = nexttag;
    2405        5520 :         targettaghash = PredicateLockTargetTagHashCode(&parenttag);
    2406             :         parentlock = (LOCALPREDICATELOCK *)
    2407        5520 :             hash_search_with_hash_value(LocalPredicateLockHash,
    2408             :                                         &parenttag, targettaghash,
    2409             :                                         HASH_FIND, NULL);
    2410             : 
    2411             :         /*
    2412             :          * There's a small chance the parent lock doesn't exist in the lock
    2413             :          * table. This can happen if we prematurely removed it because an
    2414             :          * index split caused the child refcount to be off.
    2415             :          */
    2416        5520 :         if (parentlock == NULL)
    2417           0 :             continue;
    2418             : 
    2419        5520 :         parentlock->childLocks--;
    2420             : 
    2421             :         /*
    2422             :          * Under similar circumstances the parent lock's refcount might be
    2423             :          * zero. This only happens if we're holding that lock (otherwise we
    2424             :          * would have removed the entry).
    2425             :          */
    2426        5520 :         if (parentlock->childLocks < 0)
    2427             :         {
    2428             :             Assert(parentlock->held);
    2429           0 :             parentlock->childLocks = 0;
    2430             :         }
    2431             : 
    2432        5520 :         if ((parentlock->childLocks == 0) && (!parentlock->held))
    2433             :         {
    2434             :             rmlock = (LOCALPREDICATELOCK *)
    2435        1500 :                 hash_search_with_hash_value(LocalPredicateLockHash,
    2436             :                                             &parenttag, targettaghash,
    2437             :                                             HASH_REMOVE, NULL);
    2438             :             Assert(rmlock == parentlock);
    2439             :         }
    2440             :     }
    2441        2760 : }
    2442             : 
    2443             : /*
    2444             :  * Indicate that a predicate lock on the given target is held by the
    2445             :  * specified transaction. Has no effect if the lock is already held.
    2446             :  *
    2447             :  * This updates the lock table and the sxact's lock list, and creates
    2448             :  * the lock target if necessary, but does *not* do anything related to
    2449             :  * granularity promotion or the local lock table. See
    2450             :  * PredicateLockAcquire for that.
    2451             :  */
    2452             : static void
    2453        8420 : CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag,
    2454             :                     uint32 targettaghash,
    2455             :                     SERIALIZABLEXACT *sxact)
    2456             : {
    2457             :     PREDICATELOCKTARGET *target;
    2458             :     PREDICATELOCKTAG locktag;
    2459             :     PREDICATELOCK *lock;
    2460             :     LWLock     *partitionLock;
    2461             :     bool        found;
    2462             : 
    2463        8420 :     partitionLock = PredicateLockHashPartitionLock(targettaghash);
    2464             : 
    2465        8420 :     LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    2466        8420 :     if (IsInParallelMode())
    2467          32 :         LWLockAcquire(&sxact->perXactPredicateListLock, LW_EXCLUSIVE);
    2468        8420 :     LWLockAcquire(partitionLock, LW_EXCLUSIVE);
    2469             : 
    2470             :     /* Make sure that the target is represented. */
    2471             :     target = (PREDICATELOCKTARGET *)
    2472        8420 :         hash_search_with_hash_value(PredicateLockTargetHash,
    2473             :                                     targettag, targettaghash,
    2474             :                                     HASH_ENTER_NULL, &found);
    2475        8420 :     if (!target)
    2476           0 :         ereport(ERROR,
    2477             :                 (errcode(ERRCODE_OUT_OF_MEMORY),
    2478             :                  errmsg("out of shared memory"),
    2479             :                  errhint("You might need to increase \"%s\".", "max_pred_locks_per_transaction")));
    2480        8420 :     if (!found)
    2481        6486 :         dlist_init(&target->predicateLocks);
    2482             : 
    2483             :     /* We've got the sxact and target, make sure they're joined. */
    2484        8420 :     locktag.myTarget = target;
    2485        8420 :     locktag.myXact = sxact;
    2486             :     lock = (PREDICATELOCK *)
    2487        8420 :         hash_search_with_hash_value(PredicateLockHash, &locktag,
    2488        8420 :                                     PredicateLockHashCodeFromTargetHashCode(&locktag, targettaghash),
    2489             :                                     HASH_ENTER_NULL, &found);
    2490        8420 :     if (!lock)
    2491           0 :         ereport(ERROR,
    2492             :                 (errcode(ERRCODE_OUT_OF_MEMORY),
    2493             :                  errmsg("out of shared memory"),
    2494             :                  errhint("You might need to increase \"%s\".", "max_pred_locks_per_transaction")));
    2495             : 
    2496        8420 :     if (!found)
    2497             :     {
    2498        8408 :         dlist_push_tail(&target->predicateLocks, &lock->targetLink);
    2499        8408 :         dlist_push_tail(&sxact->predicateLocks, &lock->xactLink);
    2500        8408 :         lock->commitSeqNo = InvalidSerCommitSeqNo;
    2501             :     }
    2502             : 
    2503        8420 :     LWLockRelease(partitionLock);
    2504        8420 :     if (IsInParallelMode())
    2505          32 :         LWLockRelease(&sxact->perXactPredicateListLock);
    2506        8420 :     LWLockRelease(SerializablePredicateListLock);
    2507        8420 : }
    2508             : 
    2509             : /*
    2510             :  * Acquire a predicate lock on the specified target for the current
    2511             :  * connection if not already held. This updates the local lock table
    2512             :  * and uses it to implement granularity promotion. It will consolidate
    2513             :  * multiple locks into a coarser lock if warranted, and will release
    2514             :  * any finer-grained locks covered by the new one.
    2515             :  */
    2516             : static void
    2517       52462 : PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag)
    2518             : {
    2519             :     uint32      targettaghash;
    2520             :     bool        found;
    2521             :     LOCALPREDICATELOCK *locallock;
    2522             : 
    2523             :     /* Do we have the lock already, or a covering lock? */
    2524       52462 :     if (PredicateLockExists(targettag))
    2525       44042 :         return;
    2526             : 
    2527       52062 :     if (CoarserLockCovers(targettag))
    2528       43642 :         return;
    2529             : 
    2530             :     /* the same hash and LW lock apply to the lock target and the local lock. */
    2531        8420 :     targettaghash = PredicateLockTargetTagHashCode(targettag);
    2532             : 
    2533             :     /* Acquire lock in local table */
    2534             :     locallock = (LOCALPREDICATELOCK *)
    2535        8420 :         hash_search_with_hash_value(LocalPredicateLockHash,
    2536             :                                     targettag, targettaghash,
    2537             :                                     HASH_ENTER, &found);
    2538        8420 :     locallock->held = true;
    2539        8420 :     if (!found)
    2540        7754 :         locallock->childLocks = 0;
    2541             : 
    2542             :     /* Actually create the lock */
    2543        8420 :     CreatePredicateLock(targettag, targettaghash, MySerializableXact);
    2544             : 
    2545             :     /*
    2546             :      * Lock has been acquired. Check whether it should be promoted to a
    2547             :      * coarser granularity, or whether there are finer-granularity locks to
    2548             :      * clean up.
    2549             :      */
    2550        8420 :     if (CheckAndPromotePredicateLockRequest(targettag))
    2551             :     {
    2552             :         /*
    2553             :          * Lock request was promoted to a coarser-granularity lock, and that
    2554             :          * lock was acquired. It will delete this lock and any of its
    2555             :          * children, so we're done.
    2556             :          */
    2557             :     }
    2558             :     else
    2559             :     {
    2560             :         /* Clean up any finer-granularity locks */
    2561        7754 :         if (GET_PREDICATELOCKTARGETTAG_TYPE(*targettag) != PREDLOCKTAG_TUPLE)
    2562        4688 :             DeleteChildTargetLocks(targettag);
    2563             :     }
    2564             : }
    2565             : 
    2566             : 
    2567             : /*
    2568             :  *      PredicateLockRelation
    2569             :  *
    2570             :  * Gets a predicate lock at the relation level.
    2571             :  * Skip if not in full serializable transaction isolation level.
    2572             :  * Skip if this is a temporary table.
    2573             :  * Clear any finer-grained predicate locks this session has on the relation.
    2574             :  */
    2575             : void
    2576      735590 : PredicateLockRelation(Relation relation, Snapshot snapshot)
    2577             : {
    2578             :     PREDICATELOCKTARGETTAG tag;
    2579             : 
    2580      735590 :     if (!SerializationNeededForRead(relation, snapshot))
    2581      734164 :         return;
    2582             : 
    2583        1426 :     SET_PREDICATELOCKTARGETTAG_RELATION(tag,
    2584             :                                         relation->rd_locator.dbOid,
    2585             :                                         relation->rd_id);
    2586        1426 :     PredicateLockAcquire(&tag);
    2587             : }
    2588             : 
    2589             : /*
    2590             :  *      PredicateLockPage
    2591             :  *
    2592             :  * Gets a predicate lock at the page level.
    2593             :  * Skip if not in full serializable transaction isolation level.
    2594             :  * Skip if this is a temporary table.
    2595             :  * Skip if a coarser predicate lock already covers this page.
    2596             :  * Clear any finer-grained predicate locks this session has on the relation.
    2597             :  */
    2598             : void
    2599    18549284 : PredicateLockPage(Relation relation, BlockNumber blkno, Snapshot snapshot)
    2600             : {
    2601             :     PREDICATELOCKTARGETTAG tag;
    2602             : 
    2603    18549284 :     if (!SerializationNeededForRead(relation, snapshot))
    2604    18546422 :         return;
    2605             : 
    2606        2862 :     SET_PREDICATELOCKTARGETTAG_PAGE(tag,
    2607             :                                     relation->rd_locator.dbOid,
    2608             :                                     relation->rd_id,
    2609             :                                     blkno);
    2610        2862 :     PredicateLockAcquire(&tag);
    2611             : }
    2612             : 
    2613             : /*
    2614             :  *      PredicateLockTID
    2615             :  *
    2616             :  * Gets a predicate lock at the tuple level.
    2617             :  * Skip if not in full serializable transaction isolation level.
    2618             :  * Skip if this is a temporary table.
    2619             :  */
    2620             : void
    2621    32716260 : PredicateLockTID(Relation relation, ItemPointer tid, Snapshot snapshot,
    2622             :                  TransactionId tuple_xid)
    2623             : {
    2624             :     PREDICATELOCKTARGETTAG tag;
    2625             : 
    2626    32716260 :     if (!SerializationNeededForRead(relation, snapshot))
    2627    32668752 :         return;
    2628             : 
    2629             :     /*
    2630             :      * Return if this xact wrote it.
    2631             :      */
    2632       47508 :     if (relation->rd_index == NULL)
    2633             :     {
    2634             :         /* If we wrote it; we already have a write lock. */
    2635       47508 :         if (TransactionIdIsCurrentTransactionId(tuple_xid))
    2636           0 :             return;
    2637             :     }
    2638             : 
    2639             :     /*
    2640             :      * Do quick-but-not-definitive test for a relation lock first.  This will
    2641             :      * never cause a return when the relation is *not* locked, but will
    2642             :      * occasionally let the check continue when there really *is* a relation
    2643             :      * level lock.
    2644             :      */
    2645       47508 :     SET_PREDICATELOCKTARGETTAG_RELATION(tag,
    2646             :                                         relation->rd_locator.dbOid,
    2647             :                                         relation->rd_id);
    2648       47508 :     if (PredicateLockExists(&tag))
    2649           0 :         return;
    2650             : 
    2651       47508 :     SET_PREDICATELOCKTARGETTAG_TUPLE(tag,
    2652             :                                      relation->rd_locator.dbOid,
    2653             :                                      relation->rd_id,
    2654             :                                      ItemPointerGetBlockNumber(tid),
    2655             :                                      ItemPointerGetOffsetNumber(tid));
    2656       47508 :     PredicateLockAcquire(&tag);
    2657             : }
    2658             : 
    2659             : 
    2660             : /*
    2661             :  *      DeleteLockTarget
    2662             :  *
    2663             :  * Remove a predicate lock target along with any locks held for it.
    2664             :  *
    2665             :  * Caller must hold SerializablePredicateListLock and the
    2666             :  * appropriate hash partition lock for the target.
    2667             :  */
    2668             : static void
    2669           0 : DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash)
    2670             : {
    2671             :     dlist_mutable_iter iter;
    2672             : 
    2673             :     Assert(LWLockHeldByMeInMode(SerializablePredicateListLock,
    2674             :                                 LW_EXCLUSIVE));
    2675             :     Assert(LWLockHeldByMe(PredicateLockHashPartitionLock(targettaghash)));
    2676             : 
    2677           0 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    2678             : 
    2679           0 :     dlist_foreach_modify(iter, &target->predicateLocks)
    2680             :     {
    2681           0 :         PREDICATELOCK *predlock =
    2682           0 :             dlist_container(PREDICATELOCK, targetLink, iter.cur);
    2683             :         bool        found;
    2684             : 
    2685           0 :         dlist_delete(&(predlock->xactLink));
    2686           0 :         dlist_delete(&(predlock->targetLink));
    2687             : 
    2688           0 :         hash_search_with_hash_value
    2689             :             (PredicateLockHash,
    2690           0 :              &predlock->tag,
    2691           0 :              PredicateLockHashCodeFromTargetHashCode(&predlock->tag,
    2692             :                                                      targettaghash),
    2693             :              HASH_REMOVE, &found);
    2694             :         Assert(found);
    2695             :     }
    2696           0 :     LWLockRelease(SerializableXactHashLock);
    2697             : 
    2698             :     /* Remove the target itself, if possible. */
    2699           0 :     RemoveTargetIfNoLongerUsed(target, targettaghash);
    2700           0 : }
    2701             : 
    2702             : 
    2703             : /*
    2704             :  *      TransferPredicateLocksToNewTarget
    2705             :  *
    2706             :  * Move or copy all the predicate locks for a lock target, for use by
    2707             :  * index page splits/combines and other things that create or replace
    2708             :  * lock targets. If 'removeOld' is true, the old locks and the target
    2709             :  * will be removed.
    2710             :  *
    2711             :  * Returns true on success, or false if we ran out of shared memory to
    2712             :  * allocate the new target or locks. Guaranteed to always succeed if
    2713             :  * removeOld is set (by using the scratch entry in PredicateLockTargetHash
    2714             :  * for scratch space).
    2715             :  *
    2716             :  * Warning: the "removeOld" option should be used only with care,
    2717             :  * because this function does not (indeed, can not) update other
    2718             :  * backends' LocalPredicateLockHash. If we are only adding new
    2719             :  * entries, this is not a problem: the local lock table is used only
    2720             :  * as a hint, so missing entries for locks that are held are
    2721             :  * OK. Having entries for locks that are no longer held, as can happen
    2722             :  * when using "removeOld", is not in general OK. We can only use it
    2723             :  * safely when replacing a lock with a coarser-granularity lock that
    2724             :  * covers it, or if we are absolutely certain that no one will need to
    2725             :  * refer to that lock in the future.
    2726             :  *
    2727             :  * Caller must hold SerializablePredicateListLock exclusively.
    2728             :  */
    2729             : static bool
    2730         138 : TransferPredicateLocksToNewTarget(PREDICATELOCKTARGETTAG oldtargettag,
    2731             :                                   PREDICATELOCKTARGETTAG newtargettag,
    2732             :                                   bool removeOld)
    2733             : {
    2734             :     uint32      oldtargettaghash;
    2735             :     LWLock     *oldpartitionLock;
    2736             :     PREDICATELOCKTARGET *oldtarget;
    2737             :     uint32      newtargettaghash;
    2738             :     LWLock     *newpartitionLock;
    2739             :     bool        found;
    2740         138 :     bool        outOfShmem = false;
    2741             : 
    2742             :     Assert(LWLockHeldByMeInMode(SerializablePredicateListLock,
    2743             :                                 LW_EXCLUSIVE));
    2744             : 
    2745         138 :     oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag);
    2746         138 :     newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag);
    2747         138 :     oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash);
    2748         138 :     newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash);
    2749             : 
    2750         138 :     if (removeOld)
    2751             :     {
    2752             :         /*
    2753             :          * Remove the dummy entry to give us scratch space, so we know we'll
    2754             :          * be able to create the new lock target.
    2755             :          */
    2756           0 :         RemoveScratchTarget(false);
    2757             :     }
    2758             : 
    2759             :     /*
    2760             :      * We must get the partition locks in ascending sequence to avoid
    2761             :      * deadlocks. If old and new partitions are the same, we must request the
    2762             :      * lock only once.
    2763             :      */
    2764         138 :     if (oldpartitionLock < newpartitionLock)
    2765             :     {
    2766          52 :         LWLockAcquire(oldpartitionLock,
    2767          52 :                       (removeOld ? LW_EXCLUSIVE : LW_SHARED));
    2768          52 :         LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
    2769             :     }
    2770          86 :     else if (oldpartitionLock > newpartitionLock)
    2771             :     {
    2772          82 :         LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
    2773          82 :         LWLockAcquire(oldpartitionLock,
    2774          82 :                       (removeOld ? LW_EXCLUSIVE : LW_SHARED));
    2775             :     }
    2776             :     else
    2777           4 :         LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
    2778             : 
    2779             :     /*
    2780             :      * Look for the old target.  If not found, that's OK; no predicate locks
    2781             :      * are affected, so we can just clean up and return. If it does exist,
    2782             :      * walk its list of predicate locks and move or copy them to the new
    2783             :      * target.
    2784             :      */
    2785         138 :     oldtarget = hash_search_with_hash_value(PredicateLockTargetHash,
    2786             :                                             &oldtargettag,
    2787             :                                             oldtargettaghash,
    2788             :                                             HASH_FIND, NULL);
    2789             : 
    2790         138 :     if (oldtarget)
    2791             :     {
    2792             :         PREDICATELOCKTARGET *newtarget;
    2793             :         PREDICATELOCKTAG newpredlocktag;
    2794             :         dlist_mutable_iter iter;
    2795             : 
    2796           0 :         newtarget = hash_search_with_hash_value(PredicateLockTargetHash,
    2797             :                                                 &newtargettag,
    2798             :                                                 newtargettaghash,
    2799             :                                                 HASH_ENTER_NULL, &found);
    2800             : 
    2801           0 :         if (!newtarget)
    2802             :         {
    2803             :             /* Failed to allocate due to insufficient shmem */
    2804           0 :             outOfShmem = true;
    2805           0 :             goto exit;
    2806             :         }
    2807             : 
    2808             :         /* If we created a new entry, initialize it */
    2809           0 :         if (!found)
    2810           0 :             dlist_init(&newtarget->predicateLocks);
    2811             : 
    2812           0 :         newpredlocktag.myTarget = newtarget;
    2813             : 
    2814             :         /*
    2815             :          * Loop through all the locks on the old target, replacing them with
    2816             :          * locks on the new target.
    2817             :          */
    2818           0 :         LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    2819             : 
    2820           0 :         dlist_foreach_modify(iter, &oldtarget->predicateLocks)
    2821             :         {
    2822           0 :             PREDICATELOCK *oldpredlock =
    2823           0 :                 dlist_container(PREDICATELOCK, targetLink, iter.cur);
    2824             :             PREDICATELOCK *newpredlock;
    2825           0 :             SerCommitSeqNo oldCommitSeqNo = oldpredlock->commitSeqNo;
    2826             : 
    2827           0 :             newpredlocktag.myXact = oldpredlock->tag.myXact;
    2828             : 
    2829           0 :             if (removeOld)
    2830             :             {
    2831           0 :                 dlist_delete(&(oldpredlock->xactLink));
    2832           0 :                 dlist_delete(&(oldpredlock->targetLink));
    2833             : 
    2834           0 :                 hash_search_with_hash_value
    2835             :                     (PredicateLockHash,
    2836           0 :                      &oldpredlock->tag,
    2837           0 :                      PredicateLockHashCodeFromTargetHashCode(&oldpredlock->tag,
    2838             :                                                              oldtargettaghash),
    2839             :                      HASH_REMOVE, &found);
    2840             :                 Assert(found);
    2841             :             }
    2842             : 
    2843             :             newpredlock = (PREDICATELOCK *)
    2844           0 :                 hash_search_with_hash_value(PredicateLockHash,
    2845             :                                             &newpredlocktag,
    2846           0 :                                             PredicateLockHashCodeFromTargetHashCode(&newpredlocktag,
    2847             :                                                                                     newtargettaghash),
    2848             :                                             HASH_ENTER_NULL,
    2849             :                                             &found);
    2850           0 :             if (!newpredlock)
    2851             :             {
    2852             :                 /* Out of shared memory. Undo what we've done so far. */
    2853           0 :                 LWLockRelease(SerializableXactHashLock);
    2854           0 :                 DeleteLockTarget(newtarget, newtargettaghash);
    2855           0 :                 outOfShmem = true;
    2856           0 :                 goto exit;
    2857             :             }
    2858           0 :             if (!found)
    2859             :             {
    2860           0 :                 dlist_push_tail(&(newtarget->predicateLocks),
    2861             :                                 &(newpredlock->targetLink));
    2862           0 :                 dlist_push_tail(&(newpredlocktag.myXact->predicateLocks),
    2863             :                                 &(newpredlock->xactLink));
    2864           0 :                 newpredlock->commitSeqNo = oldCommitSeqNo;
    2865             :             }
    2866             :             else
    2867             :             {
    2868           0 :                 if (newpredlock->commitSeqNo < oldCommitSeqNo)
    2869           0 :                     newpredlock->commitSeqNo = oldCommitSeqNo;
    2870             :             }
    2871             : 
    2872             :             Assert(newpredlock->commitSeqNo != 0);
    2873             :             Assert((newpredlock->commitSeqNo == InvalidSerCommitSeqNo)
    2874             :                    || (newpredlock->tag.myXact == OldCommittedSxact));
    2875             :         }
    2876           0 :         LWLockRelease(SerializableXactHashLock);
    2877             : 
    2878           0 :         if (removeOld)
    2879             :         {
    2880             :             Assert(dlist_is_empty(&oldtarget->predicateLocks));
    2881           0 :             RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash);
    2882             :         }
    2883             :     }
    2884             : 
    2885             : 
    2886         138 : exit:
    2887             :     /* Release partition locks in reverse order of acquisition. */
    2888         138 :     if (oldpartitionLock < newpartitionLock)
    2889             :     {
    2890          52 :         LWLockRelease(newpartitionLock);
    2891          52 :         LWLockRelease(oldpartitionLock);
    2892             :     }
    2893          86 :     else if (oldpartitionLock > newpartitionLock)
    2894             :     {
    2895          82 :         LWLockRelease(oldpartitionLock);
    2896          82 :         LWLockRelease(newpartitionLock);
    2897             :     }
    2898             :     else
    2899           4 :         LWLockRelease(newpartitionLock);
    2900             : 
    2901         138 :     if (removeOld)
    2902             :     {
    2903             :         /* We shouldn't run out of memory if we're moving locks */
    2904             :         Assert(!outOfShmem);
    2905             : 
    2906             :         /* Put the scratch entry back */
    2907           0 :         RestoreScratchTarget(false);
    2908             :     }
    2909             : 
    2910         138 :     return !outOfShmem;
    2911             : }
    2912             : 
    2913             : /*
    2914             :  * Drop all predicate locks of any granularity from the specified relation,
    2915             :  * which can be a heap relation or an index relation.  If 'transfer' is true,
    2916             :  * acquire a relation lock on the heap for any transactions with any lock(s)
    2917             :  * on the specified relation.
    2918             :  *
    2919             :  * This requires grabbing a lot of LW locks and scanning the entire lock
    2920             :  * target table for matches.  That makes this more expensive than most
    2921             :  * predicate lock management functions, but it will only be called for DDL
    2922             :  * type commands that are expensive anyway, and there are fast returns when
    2923             :  * no serializable transactions are active or the relation is temporary.
    2924             :  *
    2925             :  * We don't use the TransferPredicateLocksToNewTarget function because it
    2926             :  * acquires its own locks on the partitions of the two targets involved,
    2927             :  * and we'll already be holding all partition locks.
    2928             :  *
    2929             :  * We can't throw an error from here, because the call could be from a
    2930             :  * transaction which is not serializable.
    2931             :  *
    2932             :  * NOTE: This is currently only called with transfer set to true, but that may
    2933             :  * change.  If we decide to clean up the locks from a table on commit of a
    2934             :  * transaction which executed DROP TABLE, the false condition will be useful.
    2935             :  */
    2936             : static void
    2937       34240 : DropAllPredicateLocksFromTable(Relation relation, bool transfer)
    2938             : {
    2939             :     HASH_SEQ_STATUS seqstat;
    2940             :     PREDICATELOCKTARGET *oldtarget;
    2941             :     PREDICATELOCKTARGET *heaptarget;
    2942             :     Oid         dbId;
    2943             :     Oid         relId;
    2944             :     Oid         heapId;
    2945             :     int         i;
    2946             :     bool        isIndex;
    2947             :     bool        found;
    2948             :     uint32      heaptargettaghash;
    2949             : 
    2950             :     /*
    2951             :      * Bail out quickly if there are no serializable transactions running.
    2952             :      * It's safe to check this without taking locks because the caller is
    2953             :      * holding an ACCESS EXCLUSIVE lock on the relation.  No new locks which
    2954             :      * would matter here can be acquired while that is held.
    2955             :      */
    2956       34240 :     if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
    2957       34146 :         return;
    2958             : 
    2959         166 :     if (!PredicateLockingNeededForRelation(relation))
    2960          72 :         return;
    2961             : 
    2962          94 :     dbId = relation->rd_locator.dbOid;
    2963          94 :     relId = relation->rd_id;
    2964          94 :     if (relation->rd_index == NULL)
    2965             :     {
    2966           4 :         isIndex = false;
    2967           4 :         heapId = relId;
    2968             :     }
    2969             :     else
    2970             :     {
    2971          90 :         isIndex = true;
    2972          90 :         heapId = relation->rd_index->indrelid;
    2973             :     }
    2974             :     Assert(heapId != InvalidOid);
    2975             :     Assert(transfer || !isIndex);   /* index OID only makes sense with
    2976             :                                      * transfer */
    2977             : 
    2978             :     /* Retrieve first time needed, then keep. */
    2979          94 :     heaptargettaghash = 0;
    2980          94 :     heaptarget = NULL;
    2981             : 
    2982             :     /* Acquire locks on all lock partitions */
    2983          94 :     LWLockAcquire(SerializablePredicateListLock, LW_EXCLUSIVE);
    2984        1598 :     for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
    2985        1504 :         LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_EXCLUSIVE);
    2986          94 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    2987             : 
    2988             :     /*
    2989             :      * Remove the dummy entry to give us scratch space, so we know we'll be
    2990             :      * able to create the new lock target.
    2991             :      */
    2992          94 :     if (transfer)
    2993          94 :         RemoveScratchTarget(true);
    2994             : 
    2995             :     /* Scan through target map */
    2996          94 :     hash_seq_init(&seqstat, PredicateLockTargetHash);
    2997             : 
    2998         200 :     while ((oldtarget = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat)))
    2999             :     {
    3000             :         dlist_mutable_iter iter;
    3001             : 
    3002             :         /*
    3003             :          * Check whether this is a target which needs attention.
    3004             :          */
    3005         106 :         if (GET_PREDICATELOCKTARGETTAG_RELATION(oldtarget->tag) != relId)
    3006         106 :             continue;           /* wrong relation id */
    3007           0 :         if (GET_PREDICATELOCKTARGETTAG_DB(oldtarget->tag) != dbId)
    3008           0 :             continue;           /* wrong database id */
    3009           0 :         if (transfer && !isIndex
    3010           0 :             && GET_PREDICATELOCKTARGETTAG_TYPE(oldtarget->tag) == PREDLOCKTAG_RELATION)
    3011           0 :             continue;           /* already the right lock */
    3012             : 
    3013             :         /*
    3014             :          * If we made it here, we have work to do.  We make sure the heap
    3015             :          * relation lock exists, then we walk the list of predicate locks for
    3016             :          * the old target we found, moving all locks to the heap relation lock
    3017             :          * -- unless they already hold that.
    3018             :          */
    3019             : 
    3020             :         /*
    3021             :          * First make sure we have the heap relation target.  We only need to
    3022             :          * do this once.
    3023             :          */
    3024           0 :         if (transfer && heaptarget == NULL)
    3025             :         {
    3026             :             PREDICATELOCKTARGETTAG heaptargettag;
    3027             : 
    3028           0 :             SET_PREDICATELOCKTARGETTAG_RELATION(heaptargettag, dbId, heapId);
    3029           0 :             heaptargettaghash = PredicateLockTargetTagHashCode(&heaptargettag);
    3030           0 :             heaptarget = hash_search_with_hash_value(PredicateLockTargetHash,
    3031             :                                                      &heaptargettag,
    3032             :                                                      heaptargettaghash,
    3033             :                                                      HASH_ENTER, &found);
    3034           0 :             if (!found)
    3035           0 :                 dlist_init(&heaptarget->predicateLocks);
    3036             :         }
    3037             : 
    3038             :         /*
    3039             :          * Loop through all the locks on the old target, replacing them with
    3040             :          * locks on the new target.
    3041             :          */
    3042           0 :         dlist_foreach_modify(iter, &oldtarget->predicateLocks)
    3043             :         {
    3044           0 :             PREDICATELOCK *oldpredlock =
    3045           0 :                 dlist_container(PREDICATELOCK, targetLink, iter.cur);
    3046             :             PREDICATELOCK *newpredlock;
    3047             :             SerCommitSeqNo oldCommitSeqNo;
    3048             :             SERIALIZABLEXACT *oldXact;
    3049             : 
    3050             :             /*
    3051             :              * Remove the old lock first. This avoids the chance of running
    3052             :              * out of lock structure entries for the hash table.
    3053             :              */
    3054           0 :             oldCommitSeqNo = oldpredlock->commitSeqNo;
    3055           0 :             oldXact = oldpredlock->tag.myXact;
    3056             : 
    3057           0 :             dlist_delete(&(oldpredlock->xactLink));
    3058             : 
    3059             :             /*
    3060             :              * No need for retail delete from oldtarget list, we're removing
    3061             :              * the whole target anyway.
    3062             :              */
    3063           0 :             hash_search(PredicateLockHash,
    3064           0 :                         &oldpredlock->tag,
    3065             :                         HASH_REMOVE, &found);
    3066             :             Assert(found);
    3067             : 
    3068           0 :             if (transfer)
    3069             :             {
    3070             :                 PREDICATELOCKTAG newpredlocktag;
    3071             : 
    3072           0 :                 newpredlocktag.myTarget = heaptarget;
    3073           0 :                 newpredlocktag.myXact = oldXact;
    3074             :                 newpredlock = (PREDICATELOCK *)
    3075           0 :                     hash_search_with_hash_value(PredicateLockHash,
    3076             :                                                 &newpredlocktag,
    3077           0 :                                                 PredicateLockHashCodeFromTargetHashCode(&newpredlocktag,
    3078             :                                                                                         heaptargettaghash),
    3079             :                                                 HASH_ENTER,
    3080             :                                                 &found);
    3081           0 :                 if (!found)
    3082             :                 {
    3083           0 :                     dlist_push_tail(&(heaptarget->predicateLocks),
    3084             :                                     &(newpredlock->targetLink));
    3085           0 :                     dlist_push_tail(&(newpredlocktag.myXact->predicateLocks),
    3086             :                                     &(newpredlock->xactLink));
    3087           0 :                     newpredlock->commitSeqNo = oldCommitSeqNo;
    3088             :                 }
    3089             :                 else
    3090             :                 {
    3091           0 :                     if (newpredlock->commitSeqNo < oldCommitSeqNo)
    3092           0 :                         newpredlock->commitSeqNo = oldCommitSeqNo;
    3093             :                 }
    3094             : 
    3095             :                 Assert(newpredlock->commitSeqNo != 0);
    3096             :                 Assert((newpredlock->commitSeqNo == InvalidSerCommitSeqNo)
    3097             :                        || (newpredlock->tag.myXact == OldCommittedSxact));
    3098             :             }
    3099             :         }
    3100             : 
    3101           0 :         hash_search(PredicateLockTargetHash, &oldtarget->tag, HASH_REMOVE,
    3102             :                     &found);
    3103             :         Assert(found);
    3104             :     }
    3105             : 
    3106             :     /* Put the scratch entry back */
    3107          94 :     if (transfer)
    3108          94 :         RestoreScratchTarget(true);
    3109             : 
    3110             :     /* Release locks in reverse order */
    3111          94 :     LWLockRelease(SerializableXactHashLock);
    3112        1598 :     for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
    3113        1504 :         LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
    3114          94 :     LWLockRelease(SerializablePredicateListLock);
    3115             : }
    3116             : 
    3117             : /*
    3118             :  * TransferPredicateLocksToHeapRelation
    3119             :  *      For all transactions, transfer all predicate locks for the given
    3120             :  *      relation to a single relation lock on the heap.
    3121             :  */
    3122             : void
    3123       34240 : TransferPredicateLocksToHeapRelation(Relation relation)
    3124             : {
    3125       34240 :     DropAllPredicateLocksFromTable(relation, true);
    3126       34240 : }
    3127             : 
    3128             : 
    3129             : /*
    3130             :  *      PredicateLockPageSplit
    3131             :  *
    3132             :  * Copies any predicate locks for the old page to the new page.
    3133             :  * Skip if this is a temporary table or toast table.
    3134             :  *
    3135             :  * NOTE: A page split (or overflow) affects all serializable transactions,
    3136             :  * even if it occurs in the context of another transaction isolation level.
    3137             :  *
    3138             :  * NOTE: This currently leaves the local copy of the locks without
    3139             :  * information on the new lock which is in shared memory.  This could cause
    3140             :  * problems if enough page splits occur on locked pages without the processes
    3141             :  * which hold the locks getting in and noticing.
    3142             :  */
    3143             : void
    3144       59988 : PredicateLockPageSplit(Relation relation, BlockNumber oldblkno,
    3145             :                        BlockNumber newblkno)
    3146             : {
    3147             :     PREDICATELOCKTARGETTAG oldtargettag;
    3148             :     PREDICATELOCKTARGETTAG newtargettag;
    3149             :     bool        success;
    3150             : 
    3151             :     /*
    3152             :      * Bail out quickly if there are no serializable transactions running.
    3153             :      *
    3154             :      * It's safe to do this check without taking any additional locks. Even if
    3155             :      * a serializable transaction starts concurrently, we know it can't take
    3156             :      * any SIREAD locks on the page being split because the caller is holding
    3157             :      * the associated buffer page lock. Memory reordering isn't an issue; the
    3158             :      * memory barrier in the LWLock acquisition guarantees that this read
    3159             :      * occurs while the buffer page lock is held.
    3160             :      */
    3161       59988 :     if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
    3162       59850 :         return;
    3163             : 
    3164         184 :     if (!PredicateLockingNeededForRelation(relation))
    3165          46 :         return;
    3166             : 
    3167             :     Assert(oldblkno != newblkno);
    3168             :     Assert(BlockNumberIsValid(oldblkno));
    3169             :     Assert(BlockNumberIsValid(newblkno));
    3170             : 
    3171         138 :     SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag,
    3172             :                                     relation->rd_locator.dbOid,
    3173             :                                     relation->rd_id,
    3174             :                                     oldblkno);
    3175         138 :     SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag,
    3176             :                                     relation->rd_locator.dbOid,
    3177             :                                     relation->rd_id,
    3178             :                                     newblkno);
    3179             : 
    3180         138 :     LWLockAcquire(SerializablePredicateListLock, LW_EXCLUSIVE);
    3181             : 
    3182             :     /*
    3183             :      * Try copying the locks over to the new page's tag, creating it if
    3184             :      * necessary.
    3185             :      */
    3186         138 :     success = TransferPredicateLocksToNewTarget(oldtargettag,
    3187             :                                                 newtargettag,
    3188             :                                                 false);
    3189             : 
    3190         138 :     if (!success)
    3191             :     {
    3192             :         /*
    3193             :          * No more predicate lock entries are available. Failure isn't an
    3194             :          * option here, so promote the page lock to a relation lock.
    3195             :          */
    3196             : 
    3197             :         /* Get the parent relation lock's lock tag */
    3198           0 :         success = GetParentPredicateLockTag(&oldtargettag,
    3199             :                                             &newtargettag);
    3200             :         Assert(success);
    3201             : 
    3202             :         /*
    3203             :          * Move the locks to the parent. This shouldn't fail.
    3204             :          *
    3205             :          * Note that here we are removing locks held by other backends,
    3206             :          * leading to a possible inconsistency in their local lock hash table.
    3207             :          * This is OK because we're replacing it with a lock that covers the
    3208             :          * old one.
    3209             :          */
    3210           0 :         success = TransferPredicateLocksToNewTarget(oldtargettag,
    3211             :                                                     newtargettag,
    3212             :                                                     true);
    3213             :         Assert(success);
    3214             :     }
    3215             : 
    3216         138 :     LWLockRelease(SerializablePredicateListLock);
    3217             : }
    3218             : 
    3219             : /*
    3220             :  *      PredicateLockPageCombine
    3221             :  *
    3222             :  * Combines predicate locks for two existing pages.
    3223             :  * Skip if this is a temporary table or toast table.
    3224             :  *
    3225             :  * NOTE: A page combine affects all serializable transactions, even if it
    3226             :  * occurs in the context of another transaction isolation level.
    3227             :  */
    3228             : void
    3229        5524 : PredicateLockPageCombine(Relation relation, BlockNumber oldblkno,
    3230             :                          BlockNumber newblkno)
    3231             : {
    3232             :     /*
    3233             :      * Page combines differ from page splits in that we ought to be able to
    3234             :      * remove the locks on the old page after transferring them to the new
    3235             :      * page, instead of duplicating them. However, because we can't edit other
    3236             :      * backends' local lock tables, removing the old lock would leave them
    3237             :      * with an entry in their LocalPredicateLockHash for a lock they're not
    3238             :      * holding, which isn't acceptable. So we wind up having to do the same
    3239             :      * work as a page split, acquiring a lock on the new page and keeping the
    3240             :      * old page locked too. That can lead to some false positives, but should
    3241             :      * be rare in practice.
    3242             :      */
    3243        5524 :     PredicateLockPageSplit(relation, oldblkno, newblkno);
    3244        5524 : }
    3245             : 
    3246             : /*
    3247             :  * Walk the list of in-progress serializable transactions and find the new
    3248             :  * xmin.
    3249             :  */
    3250             : static void
    3251        1698 : SetNewSxactGlobalXmin(void)
    3252             : {
    3253             :     dlist_iter  iter;
    3254             : 
    3255             :     Assert(LWLockHeldByMe(SerializableXactHashLock));
    3256             : 
    3257        1698 :     PredXact->SxactGlobalXmin = InvalidTransactionId;
    3258        1698 :     PredXact->SxactGlobalXminCount = 0;
    3259             : 
    3260        6480 :     dlist_foreach(iter, &PredXact->activeList)
    3261             :     {
    3262        4782 :         SERIALIZABLEXACT *sxact =
    3263        4782 :             dlist_container(SERIALIZABLEXACT, xactLink, iter.cur);
    3264             : 
    3265        4782 :         if (!SxactIsRolledBack(sxact)
    3266        4186 :             && !SxactIsCommitted(sxact)
    3267          34 :             && sxact != OldCommittedSxact)
    3268             :         {
    3269             :             Assert(sxact->xmin != InvalidTransactionId);
    3270          34 :             if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)
    3271           0 :                 || TransactionIdPrecedes(sxact->xmin,
    3272           0 :                                          PredXact->SxactGlobalXmin))
    3273             :             {
    3274          34 :                 PredXact->SxactGlobalXmin = sxact->xmin;
    3275          34 :                 PredXact->SxactGlobalXminCount = 1;
    3276             :             }
    3277           0 :             else if (TransactionIdEquals(sxact->xmin,
    3278             :                                          PredXact->SxactGlobalXmin))
    3279           0 :                 PredXact->SxactGlobalXminCount++;
    3280             :         }
    3281             :     }
    3282             : 
    3283        1698 :     SerialSetActiveSerXmin(PredXact->SxactGlobalXmin);
    3284        1698 : }
    3285             : 
    3286             : /*
    3287             :  *      ReleasePredicateLocks
    3288             :  *
    3289             :  * Releases predicate locks based on completion of the current transaction,
    3290             :  * whether committed or rolled back.  It can also be called for a read only
    3291             :  * transaction when it becomes impossible for the transaction to become
    3292             :  * part of a dangerous structure.
    3293             :  *
    3294             :  * We do nothing unless this is a serializable transaction.
    3295             :  *
    3296             :  * This method must ensure that shared memory hash tables are cleaned
    3297             :  * up in some relatively timely fashion.
    3298             :  *
    3299             :  * If this transaction is committing and is holding any predicate locks,
    3300             :  * it must be added to a list of completed serializable transactions still
    3301             :  * holding locks.
    3302             :  *
    3303             :  * If isReadOnlySafe is true, then predicate locks are being released before
    3304             :  * the end of the transaction because MySerializableXact has been determined
    3305             :  * to be RO_SAFE.  In non-parallel mode we can release it completely, but it
    3306             :  * in parallel mode we partially release the SERIALIZABLEXACT and keep it
    3307             :  * around until the end of the transaction, allowing each backend to clear its
    3308             :  * MySerializableXact variable and benefit from the optimization in its own
    3309             :  * time.
    3310             :  */
    3311             : void
    3312      866386 : ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe)
    3313             : {
    3314      866386 :     bool        partiallyReleasing = false;
    3315             :     bool        needToClear;
    3316             :     SERIALIZABLEXACT *roXact;
    3317             :     dlist_mutable_iter iter;
    3318             : 
    3319             :     /*
    3320             :      * We can't trust XactReadOnly here, because a transaction which started
    3321             :      * as READ WRITE can show as READ ONLY later, e.g., within
    3322             :      * subtransactions.  We want to flag a transaction as READ ONLY if it
    3323             :      * commits without writing so that de facto READ ONLY transactions get the
    3324             :      * benefit of some RO optimizations, so we will use this local variable to
    3325             :      * get some cleanup logic right which is based on whether the transaction
    3326             :      * was declared READ ONLY at the top level.
    3327             :      */
    3328             :     bool        topLevelIsDeclaredReadOnly;
    3329             : 
    3330             :     /* We can't be both committing and releasing early due to RO_SAFE. */
    3331             :     Assert(!(isCommit && isReadOnlySafe));
    3332             : 
    3333             :     /* Are we at the end of a transaction, that is, a commit or abort? */
    3334      866386 :     if (!isReadOnlySafe)
    3335             :     {
    3336             :         /*
    3337             :          * Parallel workers mustn't release predicate locks at the end of
    3338             :          * their transaction.  The leader will do that at the end of its
    3339             :          * transaction.
    3340             :          */
    3341      866320 :         if (IsParallelWorker())
    3342             :         {
    3343        8220 :             ReleasePredicateLocksLocal();
    3344      863324 :             return;
    3345             :         }
    3346             : 
    3347             :         /*
    3348             :          * By the time the leader in a parallel query reaches end of
    3349             :          * transaction, it has waited for all workers to exit.
    3350             :          */
    3351             :         Assert(!ParallelContextActive());
    3352             : 
    3353             :         /*
    3354             :          * If the leader in a parallel query earlier stashed a partially
    3355             :          * released SERIALIZABLEXACT for final clean-up at end of transaction
    3356             :          * (because workers might still have been accessing it), then it's
    3357             :          * time to restore it.
    3358             :          */
    3359      858100 :         if (SavedSerializableXact != InvalidSerializableXact)
    3360             :         {
    3361             :             Assert(MySerializableXact == InvalidSerializableXact);
    3362           2 :             MySerializableXact = SavedSerializableXact;
    3363           2 :             SavedSerializableXact = InvalidSerializableXact;
    3364             :             Assert(SxactIsPartiallyReleased(MySerializableXact));
    3365             :         }
    3366             :     }
    3367             : 
    3368      858166 :     if (MySerializableXact == InvalidSerializableXact)
    3369             :     {
    3370             :         Assert(LocalPredicateLockHash == NULL);
    3371      855098 :         return;
    3372             :     }
    3373             : 
    3374        3068 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    3375             : 
    3376             :     /*
    3377             :      * If the transaction is committing, but it has been partially released
    3378             :      * already, then treat this as a roll back.  It was marked as rolled back.
    3379             :      */
    3380        3068 :     if (isCommit && SxactIsPartiallyReleased(MySerializableXact))
    3381           4 :         isCommit = false;
    3382             : 
    3383             :     /*
    3384             :      * If we're called in the middle of a transaction because we discovered
    3385             :      * that the SXACT_FLAG_RO_SAFE flag was set, then we'll partially release
    3386             :      * it (that is, release the predicate locks and conflicts, but not the
    3387             :      * SERIALIZABLEXACT itself) if we're the first backend to have noticed.
    3388             :      */
    3389        3068 :     if (isReadOnlySafe && IsInParallelMode())
    3390             :     {
    3391             :         /*
    3392             :          * The leader needs to stash a pointer to it, so that it can
    3393             :          * completely release it at end-of-transaction.
    3394             :          */
    3395          10 :         if (!IsParallelWorker())
    3396           2 :             SavedSerializableXact = MySerializableXact;
    3397             : 
    3398             :         /*
    3399             :          * The first backend to reach this condition will partially release
    3400             :          * the SERIALIZABLEXACT.  All others will just clear their
    3401             :          * backend-local state so that they stop doing SSI checks for the rest
    3402             :          * of the transaction.
    3403             :          */
    3404          10 :         if (SxactIsPartiallyReleased(MySerializableXact))
    3405             :         {
    3406           6 :             LWLockRelease(SerializableXactHashLock);
    3407           6 :             ReleasePredicateLocksLocal();
    3408           6 :             return;
    3409             :         }
    3410             :         else
    3411             :         {
    3412           4 :             MySerializableXact->flags |= SXACT_FLAG_PARTIALLY_RELEASED;
    3413           4 :             partiallyReleasing = true;
    3414             :             /* ... and proceed to perform the partial release below. */
    3415             :         }
    3416             :     }
    3417             :     Assert(!isCommit || SxactIsPrepared(MySerializableXact));
    3418             :     Assert(!isCommit || !SxactIsDoomed(MySerializableXact));
    3419             :     Assert(!SxactIsCommitted(MySerializableXact));
    3420             :     Assert(SxactIsPartiallyReleased(MySerializableXact)
    3421             :            || !SxactIsRolledBack(MySerializableXact));
    3422             : 
    3423             :     /* may not be serializable during COMMIT/ROLLBACK PREPARED */
    3424             :     Assert(MySerializableXact->pid == 0 || IsolationIsSerializable());
    3425             : 
    3426             :     /* We'd better not already be on the cleanup list. */
    3427             :     Assert(!SxactIsOnFinishedList(MySerializableXact));
    3428             : 
    3429        3062 :     topLevelIsDeclaredReadOnly = SxactIsReadOnly(MySerializableXact);
    3430             : 
    3431             :     /*
    3432             :      * We don't hold XidGenLock lock here, assuming that TransactionId is
    3433             :      * atomic!
    3434             :      *
    3435             :      * If this value is changing, we don't care that much whether we get the
    3436             :      * old or new value -- it is just used to determine how far
    3437             :      * SxactGlobalXmin must advance before this transaction can be fully
    3438             :      * cleaned up.  The worst that could happen is we wait for one more
    3439             :      * transaction to complete before freeing some RAM; correctness of visible
    3440             :      * behavior is not affected.
    3441             :      */
    3442        3062 :     MySerializableXact->finishedBefore = XidFromFullTransactionId(TransamVariables->nextXid);
    3443             : 
    3444             :     /*
    3445             :      * If it's not a commit it's either a rollback or a read-only transaction
    3446             :      * flagged SXACT_FLAG_RO_SAFE, and we can clear our locks immediately.
    3447             :      */
    3448        3062 :     if (isCommit)
    3449             :     {
    3450        2420 :         MySerializableXact->flags |= SXACT_FLAG_COMMITTED;
    3451        2420 :         MySerializableXact->commitSeqNo = ++(PredXact->LastSxactCommitSeqNo);
    3452             :         /* Recognize implicit read-only transaction (commit without write). */
    3453        2420 :         if (!MyXactDidWrite)
    3454         466 :             MySerializableXact->flags |= SXACT_FLAG_READ_ONLY;
    3455             :     }
    3456             :     else
    3457             :     {
    3458             :         /*
    3459             :          * The DOOMED flag indicates that we intend to roll back this
    3460             :          * transaction and so it should not cause serialization failures for
    3461             :          * other transactions that conflict with it. Note that this flag might
    3462             :          * already be set, if another backend marked this transaction for
    3463             :          * abort.
    3464             :          *
    3465             :          * The ROLLED_BACK flag further indicates that ReleasePredicateLocks
    3466             :          * has been called, and so the SerializableXact is eligible for
    3467             :          * cleanup. This means it should not be considered when calculating
    3468             :          * SxactGlobalXmin.
    3469             :          */
    3470         642 :         MySerializableXact->flags |= SXACT_FLAG_DOOMED;
    3471         642 :         MySerializableXact->flags |= SXACT_FLAG_ROLLED_BACK;
    3472             : 
    3473             :         /*
    3474             :          * If the transaction was previously prepared, but is now failing due
    3475             :          * to a ROLLBACK PREPARED or (hopefully very rare) error after the
    3476             :          * prepare, clear the prepared flag.  This simplifies conflict
    3477             :          * checking.
    3478             :          */
    3479         642 :         MySerializableXact->flags &= ~SXACT_FLAG_PREPARED;
    3480             :     }
    3481             : 
    3482        3062 :     if (!topLevelIsDeclaredReadOnly)
    3483             :     {
    3484             :         Assert(PredXact->WritableSxactCount > 0);
    3485        2846 :         if (--(PredXact->WritableSxactCount) == 0)
    3486             :         {
    3487             :             /*
    3488             :              * Release predicate locks and rw-conflicts in for all committed
    3489             :              * transactions.  There are no longer any transactions which might
    3490             :              * conflict with the locks and no chance for new transactions to
    3491             :              * overlap.  Similarly, existing conflicts in can't cause pivots,
    3492             :              * and any conflicts in which could have completed a dangerous
    3493             :              * structure would already have caused a rollback, so any
    3494             :              * remaining ones must be benign.
    3495             :              */
    3496        1684 :             PredXact->CanPartialClearThrough = PredXact->LastSxactCommitSeqNo;
    3497             :         }
    3498             :     }
    3499             :     else
    3500             :     {
    3501             :         /*
    3502             :          * Read-only transactions: clear the list of transactions that might
    3503             :          * make us unsafe. Note that we use 'inLink' for the iteration as
    3504             :          * opposed to 'outLink' for the r/w xacts.
    3505             :          */
    3506         300 :         dlist_foreach_modify(iter, &MySerializableXact->possibleUnsafeConflicts)
    3507             :         {
    3508          84 :             RWConflict  possibleUnsafeConflict =
    3509          84 :                 dlist_container(RWConflictData, inLink, iter.cur);
    3510             : 
    3511             :             Assert(!SxactIsReadOnly(possibleUnsafeConflict->sxactOut));
    3512             :             Assert(MySerializableXact == possibleUnsafeConflict->sxactIn);
    3513             : 
    3514          84 :             ReleaseRWConflict(possibleUnsafeConflict);
    3515             :         }
    3516             :     }
    3517             : 
    3518             :     /* Check for conflict out to old committed transactions. */
    3519        3062 :     if (isCommit
    3520        2420 :         && !SxactIsReadOnly(MySerializableXact)
    3521        1954 :         && SxactHasSummaryConflictOut(MySerializableXact))
    3522             :     {
    3523             :         /*
    3524             :          * we don't know which old committed transaction we conflicted with,
    3525             :          * so be conservative and use FirstNormalSerCommitSeqNo here
    3526             :          */
    3527           0 :         MySerializableXact->SeqNo.earliestOutConflictCommit =
    3528             :             FirstNormalSerCommitSeqNo;
    3529           0 :         MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT;
    3530             :     }
    3531             : 
    3532             :     /*
    3533             :      * Release all outConflicts to committed transactions.  If we're rolling
    3534             :      * back clear them all.  Set SXACT_FLAG_CONFLICT_OUT if any point to
    3535             :      * previously committed transactions.
    3536             :      */
    3537        4420 :     dlist_foreach_modify(iter, &MySerializableXact->outConflicts)
    3538             :     {
    3539        1358 :         RWConflict  conflict =
    3540        1358 :             dlist_container(RWConflictData, outLink, iter.cur);
    3541             : 
    3542        1358 :         if (isCommit
    3543         902 :             && !SxactIsReadOnly(MySerializableXact)
    3544         686 :             && SxactIsCommitted(conflict->sxactIn))
    3545             :         {
    3546         192 :             if ((MySerializableXact->flags & SXACT_FLAG_CONFLICT_OUT) == 0
    3547           0 :                 || conflict->sxactIn->prepareSeqNo < MySerializableXact->SeqNo.earliestOutConflictCommit)
    3548         192 :                 MySerializableXact->SeqNo.earliestOutConflictCommit = conflict->sxactIn->prepareSeqNo;
    3549         192 :             MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT;
    3550             :         }
    3551             : 
    3552        1358 :         if (!isCommit
    3553         902 :             || SxactIsCommitted(conflict->sxactIn)
    3554         666 :             || (conflict->sxactIn->SeqNo.lastCommitBeforeSnapshot >= PredXact->LastSxactCommitSeqNo))
    3555         692 :             ReleaseRWConflict(conflict);
    3556             :     }
    3557             : 
    3558             :     /*
    3559             :      * Release all inConflicts from committed and read-only transactions. If
    3560             :      * we're rolling back, clear them all.
    3561             :      */
    3562        4600 :     dlist_foreach_modify(iter, &MySerializableXact->inConflicts)
    3563             :     {
    3564        1538 :         RWConflict  conflict =
    3565        1538 :             dlist_container(RWConflictData, inLink, iter.cur);
    3566             : 
    3567        1538 :         if (!isCommit
    3568        1198 :             || SxactIsCommitted(conflict->sxactOut)
    3569         830 :             || SxactIsReadOnly(conflict->sxactOut))
    3570         868 :             ReleaseRWConflict(conflict);
    3571             :     }
    3572             : 
    3573        3062 :     if (!topLevelIsDeclaredReadOnly)
    3574             :     {
    3575             :         /*
    3576             :          * Remove ourselves from the list of possible conflicts for concurrent
    3577             :          * READ ONLY transactions, flagging them as unsafe if we have a
    3578             :          * conflict out. If any are waiting DEFERRABLE transactions, wake them
    3579             :          * up if they are known safe or known unsafe.
    3580             :          */
    3581        3026 :         dlist_foreach_modify(iter, &MySerializableXact->possibleUnsafeConflicts)
    3582             :         {
    3583         180 :             RWConflict  possibleUnsafeConflict =
    3584         180 :                 dlist_container(RWConflictData, outLink, iter.cur);
    3585             : 
    3586         180 :             roXact = possibleUnsafeConflict->sxactIn;
    3587             :             Assert(MySerializableXact == possibleUnsafeConflict->sxactOut);
    3588             :             Assert(SxactIsReadOnly(roXact));
    3589             : 
    3590             :             /* Mark conflicted if necessary. */
    3591         180 :             if (isCommit
    3592         176 :                 && MyXactDidWrite
    3593         166 :                 && SxactHasConflictOut(MySerializableXact)
    3594          26 :                 && (MySerializableXact->SeqNo.earliestOutConflictCommit
    3595          26 :                     <= roXact->SeqNo.lastCommitBeforeSnapshot))
    3596             :             {
    3597             :                 /*
    3598             :                  * This releases possibleUnsafeConflict (as well as all other
    3599             :                  * possible conflicts for roXact)
    3600             :                  */
    3601           6 :                 FlagSxactUnsafe(roXact);
    3602             :             }
    3603             :             else
    3604             :             {
    3605         174 :                 ReleaseRWConflict(possibleUnsafeConflict);
    3606             : 
    3607             :                 /*
    3608             :                  * If we were the last possible conflict, flag it safe. The
    3609             :                  * transaction can now safely release its predicate locks (but
    3610             :                  * that transaction's backend has to do that itself).
    3611             :                  */
    3612         174 :                 if (dlist_is_empty(&roXact->possibleUnsafeConflicts))
    3613         130 :                     roXact->flags |= SXACT_FLAG_RO_SAFE;
    3614             :             }
    3615             : 
    3616             :             /*
    3617             :              * Wake up the process for a waiting DEFERRABLE transaction if we
    3618             :              * now know it's either safe or conflicted.
    3619             :              */
    3620         180 :             if (SxactIsDeferrableWaiting(roXact) &&
    3621           2 :                 (SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact)))
    3622           2 :                 ProcSendSignal(roXact->pgprocno);
    3623             :         }
    3624             :     }
    3625             : 
    3626             :     /*
    3627             :      * Check whether it's time to clean up old transactions. This can only be
    3628             :      * done when the last serializable transaction with the oldest xmin among
    3629             :      * serializable transactions completes.  We then find the "new oldest"
    3630             :      * xmin and purge any transactions which finished before this transaction
    3631             :      * was launched.
    3632             :      *
    3633             :      * For parallel queries in read-only transactions, it might run twice. We
    3634             :      * only release the reference on the first call.
    3635             :      */
    3636        3062 :     needToClear = false;
    3637        3062 :     if ((partiallyReleasing ||
    3638        3058 :          !SxactIsPartiallyReleased(MySerializableXact)) &&
    3639        3058 :         TransactionIdEquals(MySerializableXact->xmin,
    3640             :                             PredXact->SxactGlobalXmin))
    3641             :     {
    3642             :         Assert(PredXact->SxactGlobalXminCount > 0);
    3643        3024 :         if (--(PredXact->SxactGlobalXminCount) == 0)
    3644             :         {
    3645        1698 :             SetNewSxactGlobalXmin();
    3646        1698 :             needToClear = true;
    3647             :         }
    3648             :     }
    3649             : 
    3650        3062 :     LWLockRelease(SerializableXactHashLock);
    3651             : 
    3652        3062 :     LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
    3653             : 
    3654             :     /* Add this to the list of transactions to check for later cleanup. */
    3655        3062 :     if (isCommit)
    3656        2420 :         dlist_push_tail(FinishedSerializableTransactions,
    3657        2420 :                         &MySerializableXact->finishedLink);
    3658             : 
    3659             :     /*
    3660             :      * If we're releasing a RO_SAFE transaction in parallel mode, we'll only
    3661             :      * partially release it.  That's necessary because other backends may have
    3662             :      * a reference to it.  The leader will release the SERIALIZABLEXACT itself
    3663             :      * at the end of the transaction after workers have stopped running.
    3664             :      */
    3665        3062 :     if (!isCommit)
    3666         642 :         ReleaseOneSerializableXact(MySerializableXact,
    3667         642 :                                    isReadOnlySafe && IsInParallelMode(),
    3668             :                                    false);
    3669             : 
    3670        3062 :     LWLockRelease(SerializableFinishedListLock);
    3671             : 
    3672        3062 :     if (needToClear)
    3673        1698 :         ClearOldPredicateLocks();
    3674             : 
    3675        3062 :     ReleasePredicateLocksLocal();
    3676             : }
    3677             : 
    3678             : static void
    3679       11288 : ReleasePredicateLocksLocal(void)
    3680             : {
    3681       11288 :     MySerializableXact = InvalidSerializableXact;
    3682       11288 :     MyXactDidWrite = false;
    3683             : 
    3684             :     /* Delete per-transaction lock table */
    3685       11288 :     if (LocalPredicateLockHash != NULL)
    3686             :     {
    3687        3060 :         hash_destroy(LocalPredicateLockHash);
    3688        3060 :         LocalPredicateLockHash = NULL;
    3689             :     }
    3690       11288 : }
    3691             : 
    3692             : /*
    3693             :  * Clear old predicate locks, belonging to committed transactions that are no
    3694             :  * longer interesting to any in-progress transaction.
    3695             :  */
    3696             : static void
    3697        1698 : ClearOldPredicateLocks(void)
    3698             : {
    3699             :     dlist_mutable_iter iter;
    3700             : 
    3701             :     /*
    3702             :      * Loop through finished transactions. They are in commit order, so we can
    3703             :      * stop as soon as we find one that's still interesting.
    3704             :      */
    3705        1698 :     LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
    3706        1698 :     LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    3707        4134 :     dlist_foreach_modify(iter, FinishedSerializableTransactions)
    3708             :     {
    3709        2452 :         SERIALIZABLEXACT *finishedSxact =
    3710        2452 :             dlist_container(SERIALIZABLEXACT, finishedLink, iter.cur);
    3711             : 
    3712        2452 :         if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)
    3713          54 :             || TransactionIdPrecedesOrEquals(finishedSxact->finishedBefore,
    3714          54 :                                              PredXact->SxactGlobalXmin))
    3715             :         {
    3716             :             /*
    3717             :              * This transaction committed before any in-progress transaction
    3718             :              * took its snapshot. It's no longer interesting.
    3719             :              */
    3720        2420 :             LWLockRelease(SerializableXactHashLock);
    3721        2420 :             dlist_delete_thoroughly(&finishedSxact->finishedLink);
    3722        2420 :             ReleaseOneSerializableXact(finishedSxact, false, false);
    3723        2420 :             LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    3724             :         }
    3725          32 :         else if (finishedSxact->commitSeqNo > PredXact->HavePartialClearedThrough
    3726          32 :                  && finishedSxact->commitSeqNo <= PredXact->CanPartialClearThrough)
    3727             :         {
    3728             :             /*
    3729             :              * Any active transactions that took their snapshot before this
    3730             :              * transaction committed are read-only, so we can clear part of
    3731             :              * its state.
    3732             :              */
    3733          16 :             LWLockRelease(SerializableXactHashLock);
    3734             : 
    3735          16 :             if (SxactIsReadOnly(finishedSxact))
    3736             :             {
    3737             :                 /* A read-only transaction can be removed entirely */
    3738           0 :                 dlist_delete_thoroughly(&(finishedSxact->finishedLink));
    3739           0 :                 ReleaseOneSerializableXact(finishedSxact, false, false);
    3740             :             }
    3741             :             else
    3742             :             {
    3743             :                 /*
    3744             :                  * A read-write transaction can only be partially cleared. We
    3745             :                  * need to keep the SERIALIZABLEXACT but can release the
    3746             :                  * SIREAD locks and conflicts in.
    3747             :                  */
    3748          16 :                 ReleaseOneSerializableXact(finishedSxact, true, false);
    3749             :             }
    3750             : 
    3751          16 :             PredXact->HavePartialClearedThrough = finishedSxact->commitSeqNo;
    3752          16 :             LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    3753             :         }
    3754             :         else
    3755             :         {
    3756             :             /* Still interesting. */
    3757             :             break;
    3758             :         }
    3759             :     }
    3760        1698 :     LWLockRelease(SerializableXactHashLock);
    3761             : 
    3762             :     /*
    3763             :      * Loop through predicate locks on dummy transaction for summarized data.
    3764             :      */
    3765        1698 :     LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    3766        1698 :     dlist_foreach_modify(iter, &OldCommittedSxact->predicateLocks)
    3767             :     {
    3768           0 :         PREDICATELOCK *predlock =
    3769           0 :             dlist_container(PREDICATELOCK, xactLink, iter.cur);
    3770             :         bool        canDoPartialCleanup;
    3771             : 
    3772           0 :         LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    3773             :         Assert(predlock->commitSeqNo != 0);
    3774             :         Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
    3775           0 :         canDoPartialCleanup = (predlock->commitSeqNo <= PredXact->CanPartialClearThrough);
    3776           0 :         LWLockRelease(SerializableXactHashLock);
    3777             : 
    3778             :         /*
    3779             :          * If this lock originally belonged to an old enough transaction, we
    3780             :          * can release it.
    3781             :          */
    3782           0 :         if (canDoPartialCleanup)
    3783             :         {
    3784             :             PREDICATELOCKTAG tag;
    3785             :             PREDICATELOCKTARGET *target;
    3786             :             PREDICATELOCKTARGETTAG targettag;
    3787             :             uint32      targettaghash;
    3788             :             LWLock     *partitionLock;
    3789             : 
    3790           0 :             tag = predlock->tag;
    3791           0 :             target = tag.myTarget;
    3792           0 :             targettag = target->tag;
    3793           0 :             targettaghash = PredicateLockTargetTagHashCode(&targettag);
    3794           0 :             partitionLock = PredicateLockHashPartitionLock(targettaghash);
    3795             : 
    3796           0 :             LWLockAcquire(partitionLock, LW_EXCLUSIVE);
    3797             : 
    3798           0 :             dlist_delete(&(predlock->targetLink));
    3799           0 :             dlist_delete(&(predlock->xactLink));
    3800             : 
    3801           0 :             hash_search_with_hash_value(PredicateLockHash, &tag,
    3802           0 :                                         PredicateLockHashCodeFromTargetHashCode(&tag,
    3803             :                                                                                 targettaghash),
    3804             :                                         HASH_REMOVE, NULL);
    3805           0 :             RemoveTargetIfNoLongerUsed(target, targettaghash);
    3806             : 
    3807           0 :             LWLockRelease(partitionLock);
    3808             :         }
    3809             :     }
    3810             : 
    3811        1698 :     LWLockRelease(SerializablePredicateListLock);
    3812        1698 :     LWLockRelease(SerializableFinishedListLock);
    3813        1698 : }
    3814             : 
    3815             : /*
    3816             :  * This is the normal way to delete anything from any of the predicate
    3817             :  * locking hash tables.  Given a transaction which we know can be deleted:
    3818             :  * delete all predicate locks held by that transaction and any predicate
    3819             :  * lock targets which are now unreferenced by a lock; delete all conflicts
    3820             :  * for the transaction; delete all xid values for the transaction; then
    3821             :  * delete the transaction.
    3822             :  *
    3823             :  * When the partial flag is set, we can release all predicate locks and
    3824             :  * in-conflict information -- we've established that there are no longer
    3825             :  * any overlapping read write transactions for which this transaction could
    3826             :  * matter -- but keep the transaction entry itself and any outConflicts.
    3827             :  *
    3828             :  * When the summarize flag is set, we've run short of room for sxact data
    3829             :  * and must summarize to the SLRU.  Predicate locks are transferred to a
    3830             :  * dummy "old" transaction, with duplicate locks on a single target
    3831             :  * collapsing to a single lock with the "latest" commitSeqNo from among
    3832             :  * the conflicting locks..
    3833             :  */
    3834             : static void
    3835        3078 : ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
    3836             :                            bool summarize)
    3837             : {
    3838             :     SERIALIZABLEXIDTAG sxidtag;
    3839             :     dlist_mutable_iter iter;
    3840             : 
    3841             :     Assert(sxact != NULL);
    3842             :     Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact));
    3843             :     Assert(partial || !SxactIsOnFinishedList(sxact));
    3844             :     Assert(LWLockHeldByMe(SerializableFinishedListLock));
    3845             : 
    3846             :     /*
    3847             :      * First release all the predicate locks held by this xact (or transfer
    3848             :      * them to OldCommittedSxact if summarize is true)
    3849             :      */
    3850        3078 :     LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    3851        3078 :     if (IsInParallelMode())
    3852           6 :         LWLockAcquire(&sxact->perXactPredicateListLock, LW_EXCLUSIVE);
    3853        8726 :     dlist_foreach_modify(iter, &sxact->predicateLocks)
    3854             :     {
    3855        5648 :         PREDICATELOCK *predlock =
    3856        5648 :             dlist_container(PREDICATELOCK, xactLink, iter.cur);
    3857             :         PREDICATELOCKTAG tag;
    3858             :         PREDICATELOCKTARGET *target;
    3859             :         PREDICATELOCKTARGETTAG targettag;
    3860             :         uint32      targettaghash;
    3861             :         LWLock     *partitionLock;
    3862             : 
    3863        5648 :         tag = predlock->tag;
    3864        5648 :         target = tag.myTarget;
    3865        5648 :         targettag = target->tag;
    3866        5648 :         targettaghash = PredicateLockTargetTagHashCode(&targettag);
    3867        5648 :         partitionLock = PredicateLockHashPartitionLock(targettaghash);
    3868             : 
    3869        5648 :         LWLockAcquire(partitionLock, LW_EXCLUSIVE);
    3870             : 
    3871        5648 :         dlist_delete(&predlock->targetLink);
    3872             : 
    3873        5648 :         hash_search_with_hash_value(PredicateLockHash, &tag,
    3874        5648 :                                     PredicateLockHashCodeFromTargetHashCode(&tag,
    3875             :                                                                             targettaghash),
    3876             :                                     HASH_REMOVE, NULL);
    3877        5648 :         if (summarize)
    3878             :         {
    3879             :             bool        found;
    3880             : 
    3881             :             /* Fold into dummy transaction list. */
    3882           0 :             tag.myXact = OldCommittedSxact;
    3883           0 :             predlock = hash_search_with_hash_value(PredicateLockHash, &tag,
    3884           0 :                                                    PredicateLockHashCodeFromTargetHashCode(&tag,
    3885             :                                                                                            targettaghash),
    3886             :                                                    HASH_ENTER_NULL, &found);
    3887           0 :             if (!predlock)
    3888           0 :                 ereport(ERROR,
    3889             :                         (errcode(ERRCODE_OUT_OF_MEMORY),
    3890             :                          errmsg("out of shared memory"),
    3891             :                          errhint("You might need to increase \"%s\".", "max_pred_locks_per_transaction")));
    3892           0 :             if (found)
    3893             :             {
    3894             :                 Assert(predlock->commitSeqNo != 0);
    3895             :                 Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
    3896           0 :                 if (predlock->commitSeqNo < sxact->commitSeqNo)
    3897           0 :                     predlock->commitSeqNo = sxact->commitSeqNo;
    3898             :             }
    3899             :             else
    3900             :             {
    3901           0 :                 dlist_push_tail(&target->predicateLocks,
    3902             :                                 &predlock->targetLink);
    3903           0 :                 dlist_push_tail(&OldCommittedSxact->predicateLocks,
    3904             :                                 &predlock->xactLink);
    3905           0 :                 predlock->commitSeqNo = sxact->commitSeqNo;
    3906             :             }
    3907             :         }
    3908             :         else
    3909        5648 :             RemoveTargetIfNoLongerUsed(target, targettaghash);
    3910             : 
    3911        5648 :         LWLockRelease(partitionLock);
    3912             :     }
    3913             : 
    3914             :     /*
    3915             :      * Rather than retail removal, just re-init the head after we've run
    3916             :      * through the list.
    3917             :      */
    3918        3078 :     dlist_init(&sxact->predicateLocks);
    3919             : 
    3920        3078 :     if (IsInParallelMode())
    3921           6 :         LWLockRelease(&sxact->perXactPredicateListLock);
    3922        3078 :     LWLockRelease(SerializablePredicateListLock);
    3923             : 
    3924        3078 :     sxidtag.xid = sxact->topXid;
    3925        3078 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    3926             : 
    3927             :     /* Release all outConflicts (unless 'partial' is true) */
    3928        3078 :     if (!partial)
    3929             :     {
    3930        3058 :         dlist_foreach_modify(iter, &sxact->outConflicts)
    3931             :         {
    3932           0 :             RWConflict  conflict =
    3933           0 :                 dlist_container(RWConflictData, outLink, iter.cur);
    3934             : 
    3935           0 :             if (summarize)
    3936           0 :                 conflict->sxactIn->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
    3937           0 :             ReleaseRWConflict(conflict);
    3938             :         }
    3939             :     }
    3940             : 
    3941             :     /* Release all inConflicts. */
    3942        3078 :     dlist_foreach_modify(iter, &sxact->inConflicts)
    3943             :     {
    3944           0 :         RWConflict  conflict =
    3945           0 :             dlist_container(RWConflictData, inLink, iter.cur);
    3946             : 
    3947           0 :         if (summarize)
    3948           0 :             conflict->sxactOut->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
    3949           0 :         ReleaseRWConflict(conflict);
    3950             :     }
    3951             : 
    3952             :     /* Finally, get rid of the xid and the record of the transaction itself. */
    3953        3078 :     if (!partial)
    3954             :     {
    3955        3058 :         if (sxidtag.xid != InvalidTransactionId)
    3956        2526 :             hash_search(SerializableXidHash, &sxidtag, HASH_REMOVE, NULL);
    3957        3058 :         ReleasePredXact(sxact);
    3958             :     }
    3959             : 
    3960        3078 :     LWLockRelease(SerializableXactHashLock);
    3961        3078 : }
    3962             : 
    3963             : /*
    3964             :  * Tests whether the given top level transaction is concurrent with
    3965             :  * (overlaps) our current transaction.
    3966             :  *
    3967             :  * We need to identify the top level transaction for SSI, anyway, so pass
    3968             :  * that to this function to save the overhead of checking the snapshot's
    3969             :  * subxip array.
    3970             :  */
    3971             : static bool
    3972        1064 : XidIsConcurrent(TransactionId xid)
    3973             : {
    3974             :     Snapshot    snap;
    3975             : 
    3976             :     Assert(TransactionIdIsValid(xid));
    3977             :     Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny()));
    3978             : 
    3979        1064 :     snap = GetTransactionSnapshot();
    3980             : 
    3981        1064 :     if (TransactionIdPrecedes(xid, snap->xmin))
    3982           0 :         return false;
    3983             : 
    3984        1064 :     if (TransactionIdFollowsOrEquals(xid, snap->xmax))
    3985        1048 :         return true;
    3986             : 
    3987          16 :     return pg_lfind32(xid, snap->xip, snap->xcnt);
    3988             : }
    3989             : 
    3990             : bool
    3991    68981086 : CheckForSerializableConflictOutNeeded(Relation relation, Snapshot snapshot)
    3992             : {
    3993    68981086 :     if (!SerializationNeededForRead(relation, snapshot))
    3994    68929178 :         return false;
    3995             : 
    3996             :     /* Check if someone else has already decided that we need to die */
    3997       51908 :     if (SxactIsDoomed(MySerializableXact))
    3998             :     {
    3999           0 :         ereport(ERROR,
    4000             :                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4001             :                  errmsg("could not serialize access due to read/write dependencies among transactions"),
    4002             :                  errdetail_internal("Reason code: Canceled on identification as a pivot, during conflict out checking."),
    4003             :                  errhint("The transaction might succeed if retried.")));
    4004             :     }
    4005             : 
    4006       51908 :     return true;
    4007             : }
    4008             : 
    4009             : /*
    4010             :  * CheckForSerializableConflictOut
    4011             :  *      A table AM is reading a tuple that has been modified.  If it determines
    4012             :  *      that the tuple version it is reading is not visible to us, it should
    4013             :  *      pass in the top level xid of the transaction that created it.
    4014             :  *      Otherwise, if it determines that it is visible to us but it has been
    4015             :  *      deleted or there is a newer version available due to an update, it
    4016             :  *      should pass in the top level xid of the modifying transaction.
    4017             :  *
    4018             :  * This function will check for overlap with our own transaction.  If the given
    4019             :  * xid is also serializable and the transactions overlap (i.e., they cannot see
    4020             :  * each other's writes), then we have a conflict out.
    4021             :  */
    4022             : void
    4023        1130 : CheckForSerializableConflictOut(Relation relation, TransactionId xid, Snapshot snapshot)
    4024             : {
    4025             :     SERIALIZABLEXIDTAG sxidtag;
    4026             :     SERIALIZABLEXID *sxid;
    4027             :     SERIALIZABLEXACT *sxact;
    4028             : 
    4029        1130 :     if (!SerializationNeededForRead(relation, snapshot))
    4030         404 :         return;
    4031             : 
    4032             :     /* Check if someone else has already decided that we need to die */
    4033        1130 :     if (SxactIsDoomed(MySerializableXact))
    4034             :     {
    4035           0 :         ereport(ERROR,
    4036             :                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4037             :                  errmsg("could not serialize access due to read/write dependencies among transactions"),
    4038             :                  errdetail_internal("Reason code: Canceled on identification as a pivot, during conflict out checking."),
    4039             :                  errhint("The transaction might succeed if retried.")));
    4040             :     }
    4041             :     Assert(TransactionIdIsValid(xid));
    4042             : 
    4043        1130 :     if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
    4044           0 :         return;
    4045             : 
    4046             :     /*
    4047             :      * Find sxact or summarized info for the top level xid.
    4048             :      */
    4049        1130 :     sxidtag.xid = xid;
    4050        1130 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4051             :     sxid = (SERIALIZABLEXID *)
    4052        1130 :         hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
    4053        1130 :     if (!sxid)
    4054             :     {
    4055             :         /*
    4056             :          * Transaction not found in "normal" SSI structures.  Check whether it
    4057             :          * got pushed out to SLRU storage for "old committed" transactions.
    4058             :          */
    4059             :         SerCommitSeqNo conflictCommitSeqNo;
    4060             : 
    4061          46 :         conflictCommitSeqNo = SerialGetMinConflictCommitSeqNo(xid);
    4062          46 :         if (conflictCommitSeqNo != 0)
    4063             :         {
    4064           0 :             if (conflictCommitSeqNo != InvalidSerCommitSeqNo
    4065           0 :                 && (!SxactIsReadOnly(MySerializableXact)
    4066           0 :                     || conflictCommitSeqNo
    4067           0 :                     <= MySerializableXact->SeqNo.lastCommitBeforeSnapshot))
    4068           0 :                 ereport(ERROR,
    4069             :                         (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4070             :                          errmsg("could not serialize access due to read/write dependencies among transactions"),
    4071             :                          errdetail_internal("Reason code: Canceled on conflict out to old pivot %u.", xid),
    4072             :                          errhint("The transaction might succeed if retried.")));
    4073             : 
    4074           0 :             if (SxactHasSummaryConflictIn(MySerializableXact)
    4075           0 :                 || !dlist_is_empty(&MySerializableXact->inConflicts))
    4076           0 :                 ereport(ERROR,
    4077             :                         (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4078             :                          errmsg("could not serialize access due to read/write dependencies among transactions"),
    4079             :                          errdetail_internal("Reason code: Canceled on identification as a pivot, with conflict out to old committed transaction %u.", xid),
    4080             :                          errhint("The transaction might succeed if retried.")));
    4081             : 
    4082           0 :             MySerializableXact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
    4083             :         }
    4084             : 
    4085             :         /* It's not serializable or otherwise not important. */
    4086          46 :         LWLockRelease(SerializableXactHashLock);
    4087          46 :         return;
    4088             :     }
    4089        1084 :     sxact = sxid->myXact;
    4090             :     Assert(TransactionIdEquals(sxact->topXid, xid));
    4091        1084 :     if (sxact == MySerializableXact || SxactIsDoomed(sxact))
    4092             :     {
    4093             :         /* Can't conflict with ourself or a transaction that will roll back. */
    4094           8 :         LWLockRelease(SerializableXactHashLock);
    4095           8 :         return;
    4096             :     }
    4097             : 
    4098             :     /*
    4099             :      * We have a conflict out to a transaction which has a conflict out to a
    4100             :      * summarized transaction.  That summarized transaction must have
    4101             :      * committed first, and we can't tell when it committed in relation to our
    4102             :      * snapshot acquisition, so something needs to be canceled.
    4103             :      */
    4104        1076 :     if (SxactHasSummaryConflictOut(sxact))
    4105             :     {
    4106           0 :         if (!SxactIsPrepared(sxact))
    4107             :         {
    4108           0 :             sxact->flags |= SXACT_FLAG_DOOMED;
    4109           0 :             LWLockRelease(SerializableXactHashLock);
    4110           0 :             return;
    4111             :         }
    4112             :         else
    4113             :         {
    4114           0 :             LWLockRelease(SerializableXactHashLock);
    4115           0 :             ereport(ERROR,
    4116             :                     (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4117             :                      errmsg("could not serialize access due to read/write dependencies among transactions"),
    4118             :                      errdetail_internal("Reason code: Canceled on conflict out to old pivot."),
    4119             :                      errhint("The transaction might succeed if retried.")));
    4120             :         }
    4121             :     }
    4122             : 
    4123             :     /*
    4124             :      * If this is a read-only transaction and the writing transaction has
    4125             :      * committed, and it doesn't have a rw-conflict to a transaction which
    4126             :      * committed before it, no conflict.
    4127             :      */
    4128        1076 :     if (SxactIsReadOnly(MySerializableXact)
    4129         238 :         && SxactIsCommitted(sxact)
    4130          16 :         && !SxactHasSummaryConflictOut(sxact)
    4131          16 :         && (!SxactHasConflictOut(sxact)
    4132           4 :             || MySerializableXact->SeqNo.lastCommitBeforeSnapshot < sxact->SeqNo.earliestOutConflictCommit))
    4133             :     {
    4134             :         /* Read-only transaction will appear to run first.  No conflict. */
    4135          12 :         LWLockRelease(SerializableXactHashLock);
    4136          12 :         return;
    4137             :     }
    4138             : 
    4139        1064 :     if (!XidIsConcurrent(xid))
    4140             :     {
    4141             :         /* This write was already in our snapshot; no conflict. */
    4142           0 :         LWLockRelease(SerializableXactHashLock);
    4143           0 :         return;
    4144             :     }
    4145             : 
    4146        1064 :     if (RWConflictExists(MySerializableXact, sxact))
    4147             :     {
    4148             :         /* We don't want duplicate conflict records in the list. */
    4149         338 :         LWLockRelease(SerializableXactHashLock);
    4150         338 :         return;
    4151             :     }
    4152             : 
    4153             :     /*
    4154             :      * Flag the conflict.  But first, if this conflict creates a dangerous
    4155             :      * structure, ereport an error.
    4156             :      */
    4157         726 :     FlagRWConflict(MySerializableXact, sxact);
    4158         700 :     LWLockRelease(SerializableXactHashLock);
    4159             : }
    4160             : 
    4161             : /*
    4162             :  * Check a particular target for rw-dependency conflict in. A subroutine of
    4163             :  * CheckForSerializableConflictIn().
    4164             :  */
    4165             : static void
    4166       14956 : CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
    4167             : {
    4168             :     uint32      targettaghash;
    4169             :     LWLock     *partitionLock;
    4170             :     PREDICATELOCKTARGET *target;
    4171       14956 :     PREDICATELOCK *mypredlock = NULL;
    4172             :     PREDICATELOCKTAG mypredlocktag;
    4173             :     dlist_mutable_iter iter;
    4174             : 
    4175             :     Assert(MySerializableXact != InvalidSerializableXact);
    4176             : 
    4177             :     /*
    4178             :      * The same hash and LW lock apply to the lock target and the lock itself.
    4179             :      */
    4180       14956 :     targettaghash = PredicateLockTargetTagHashCode(targettag);
    4181       14956 :     partitionLock = PredicateLockHashPartitionLock(targettaghash);
    4182       14956 :     LWLockAcquire(partitionLock, LW_SHARED);
    4183             :     target = (PREDICATELOCKTARGET *)
    4184       14956 :         hash_search_with_hash_value(PredicateLockTargetHash,
    4185             :                                     targettag, targettaghash,
    4186             :                                     HASH_FIND, NULL);
    4187       14956 :     if (!target)
    4188             :     {
    4189             :         /* Nothing has this target locked; we're done here. */
    4190       11214 :         LWLockRelease(partitionLock);
    4191       11214 :         return;
    4192             :     }
    4193             : 
    4194             :     /*
    4195             :      * Each lock for an overlapping transaction represents a conflict: a
    4196             :      * rw-dependency in to this transaction.
    4197             :      */
    4198        3742 :     LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    4199             : 
    4200        8432 :     dlist_foreach_modify(iter, &target->predicateLocks)
    4201             :     {
    4202        4824 :         PREDICATELOCK *predlock =
    4203        4824 :             dlist_container(PREDICATELOCK, targetLink, iter.cur);
    4204        4824 :         SERIALIZABLEXACT *sxact = predlock->tag.myXact;
    4205             : 
    4206        4824 :         if (sxact == MySerializableXact)
    4207             :         {
    4208             :             /*
    4209             :              * If we're getting a write lock on a tuple, we don't need a
    4210             :              * predicate (SIREAD) lock on the same tuple. We can safely remove
    4211             :              * our SIREAD lock, but we'll defer doing so until after the loop
    4212             :              * because that requires upgrading to an exclusive partition lock.
    4213             :              *
    4214             :              * We can't use this optimization within a subtransaction because
    4215             :              * the subtransaction could roll back, and we would be left
    4216             :              * without any lock at the top level.
    4217             :              */
    4218        3128 :             if (!IsSubTransaction()
    4219        3128 :                 && GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag))
    4220             :             {
    4221         776 :                 mypredlock = predlock;
    4222         776 :                 mypredlocktag = predlock->tag;
    4223             :             }
    4224             :         }
    4225        1696 :         else if (!SxactIsDoomed(sxact)
    4226        1696 :                  && (!SxactIsCommitted(sxact)
    4227         166 :                      || TransactionIdPrecedes(GetTransactionSnapshot()->xmin,
    4228             :                                               sxact->finishedBefore))
    4229        1678 :                  && !RWConflictExists(sxact, MySerializableXact))
    4230             :         {
    4231         994 :             LWLockRelease(SerializableXactHashLock);
    4232         994 :             LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4233             : 
    4234             :             /*
    4235             :              * Re-check after getting exclusive lock because the other
    4236             :              * transaction may have flagged a conflict.
    4237             :              */
    4238         994 :             if (!SxactIsDoomed(sxact)
    4239         994 :                 && (!SxactIsCommitted(sxact)
    4240         148 :                     || TransactionIdPrecedes(GetTransactionSnapshot()->xmin,
    4241             :                                              sxact->finishedBefore))
    4242         994 :                 && !RWConflictExists(sxact, MySerializableXact))
    4243             :             {
    4244         994 :                 FlagRWConflict(sxact, MySerializableXact);
    4245             :             }
    4246             : 
    4247         860 :             LWLockRelease(SerializableXactHashLock);
    4248         860 :             LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    4249             :         }
    4250             :     }
    4251        3608 :     LWLockRelease(SerializableXactHashLock);
    4252        3608 :     LWLockRelease(partitionLock);
    4253             : 
    4254             :     /*
    4255             :      * If we found one of our own SIREAD locks to remove, remove it now.
    4256             :      *
    4257             :      * At this point our transaction already has a RowExclusiveLock on the
    4258             :      * relation, so we are OK to drop the predicate lock on the tuple, if
    4259             :      * found, without fearing that another write against the tuple will occur
    4260             :      * before the MVCC information makes it to the buffer.
    4261             :      */
    4262        3608 :     if (mypredlock != NULL)
    4263             :     {
    4264             :         uint32      predlockhashcode;
    4265             :         PREDICATELOCK *rmpredlock;
    4266             : 
    4267         762 :         LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    4268         762 :         if (IsInParallelMode())
    4269           0 :             LWLockAcquire(&MySerializableXact->perXactPredicateListLock, LW_EXCLUSIVE);
    4270         762 :         LWLockAcquire(partitionLock, LW_EXCLUSIVE);
    4271         762 :         LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4272             : 
    4273             :         /*
    4274             :          * Remove the predicate lock from shared memory, if it wasn't removed
    4275             :          * while the locks were released.  One way that could happen is from
    4276             :          * autovacuum cleaning up an index.
    4277             :          */
    4278         762 :         predlockhashcode = PredicateLockHashCodeFromTargetHashCode
    4279             :             (&mypredlocktag, targettaghash);
    4280             :         rmpredlock = (PREDICATELOCK *)
    4281         762 :             hash_search_with_hash_value(PredicateLockHash,
    4282             :                                         &mypredlocktag,
    4283             :                                         predlockhashcode,
    4284             :                                         HASH_FIND, NULL);
    4285         762 :         if (rmpredlock != NULL)
    4286             :         {
    4287             :             Assert(rmpredlock == mypredlock);
    4288             : 
    4289         762 :             dlist_delete(&(mypredlock->targetLink));
    4290         762 :             dlist_delete(&(mypredlock->xactLink));
    4291             : 
    4292             :             rmpredlock = (PREDICATELOCK *)
    4293         762 :                 hash_search_with_hash_value(PredicateLockHash,
    4294             :                                             &mypredlocktag,
    4295             :                                             predlockhashcode,
    4296             :                                             HASH_REMOVE, NULL);
    4297             :             Assert(rmpredlock == mypredlock);
    4298             : 
    4299         762 :             RemoveTargetIfNoLongerUsed(target, targettaghash);
    4300             :         }
    4301             : 
    4302         762 :         LWLockRelease(SerializableXactHashLock);
    4303         762 :         LWLockRelease(partitionLock);
    4304         762 :         if (IsInParallelMode())
    4305           0 :             LWLockRelease(&MySerializableXact->perXactPredicateListLock);
    4306         762 :         LWLockRelease(SerializablePredicateListLock);
    4307             : 
    4308         762 :         if (rmpredlock != NULL)
    4309             :         {
    4310             :             /*
    4311             :              * Remove entry in local lock table if it exists. It's OK if it
    4312             :              * doesn't exist; that means the lock was transferred to a new
    4313             :              * target by a different backend.
    4314             :              */
    4315         762 :             hash_search_with_hash_value(LocalPredicateLockHash,
    4316             :                                         targettag, targettaghash,
    4317             :                                         HASH_REMOVE, NULL);
    4318             : 
    4319         762 :             DecrementParentLocks(targettag);
    4320             :         }
    4321             :     }
    4322             : }
    4323             : 
    4324             : /*
    4325             :  * CheckForSerializableConflictIn
    4326             :  *      We are writing the given tuple.  If that indicates a rw-conflict
    4327             :  *      in from another serializable transaction, take appropriate action.
    4328             :  *
    4329             :  * Skip checking for any granularity for which a parameter is missing.
    4330             :  *
    4331             :  * A tuple update or delete is in conflict if we have a predicate lock
    4332             :  * against the relation or page in which the tuple exists, or against the
    4333             :  * tuple itself.
    4334             :  */
    4335             : void
    4336    33031888 : CheckForSerializableConflictIn(Relation relation, ItemPointer tid, BlockNumber blkno)
    4337             : {
    4338             :     PREDICATELOCKTARGETTAG targettag;
    4339             : 
    4340    33031888 :     if (!SerializationNeededForWrite(relation))
    4341    33023038 :         return;
    4342             : 
    4343             :     /* Check if someone else has already decided that we need to die */
    4344        8850 :     if (SxactIsDoomed(MySerializableXact))
    4345           2 :         ereport(ERROR,
    4346             :                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4347             :                  errmsg("could not serialize access due to read/write dependencies among transactions"),
    4348             :                  errdetail_internal("Reason code: Canceled on identification as a pivot, during conflict in checking."),
    4349             :                  errhint("The transaction might succeed if retried.")));
    4350             : 
    4351             :     /*
    4352             :      * We're doing a write which might cause rw-conflicts now or later.
    4353             :      * Memorize that fact.
    4354             :      */
    4355        8848 :     MyXactDidWrite = true;
    4356             : 
    4357             :     /*
    4358             :      * It is important that we check for locks from the finest granularity to
    4359             :      * the coarsest granularity, so that granularity promotion doesn't cause
    4360             :      * us to miss a lock.  The new (coarser) lock will be acquired before the
    4361             :      * old (finer) locks are released.
    4362             :      *
    4363             :      * It is not possible to take and hold a lock across the checks for all
    4364             :      * granularities because each target could be in a separate partition.
    4365             :      */
    4366        8848 :     if (tid != NULL)
    4367             :     {
    4368        1286 :         SET_PREDICATELOCKTARGETTAG_TUPLE(targettag,
    4369             :                                          relation->rd_locator.dbOid,
    4370             :                                          relation->rd_id,
    4371             :                                          ItemPointerGetBlockNumber(tid),
    4372             :                                          ItemPointerGetOffsetNumber(tid));
    4373        1286 :         CheckTargetForConflictsIn(&targettag);
    4374             :     }
    4375             : 
    4376        8802 :     if (blkno != InvalidBlockNumber)
    4377             :     {
    4378        4928 :         SET_PREDICATELOCKTARGETTAG_PAGE(targettag,
    4379             :                                         relation->rd_locator.dbOid,
    4380             :                                         relation->rd_id,
    4381             :                                         blkno);
    4382        4928 :         CheckTargetForConflictsIn(&targettag);
    4383             :     }
    4384             : 
    4385        8742 :     SET_PREDICATELOCKTARGETTAG_RELATION(targettag,
    4386             :                                         relation->rd_locator.dbOid,
    4387             :                                         relation->rd_id);
    4388        8742 :     CheckTargetForConflictsIn(&targettag);
    4389             : }
    4390             : 
    4391             : /*
    4392             :  * CheckTableForSerializableConflictIn
    4393             :  *      The entire table is going through a DDL-style logical mass delete
    4394             :  *      like TRUNCATE or DROP TABLE.  If that causes a rw-conflict in from
    4395             :  *      another serializable transaction, take appropriate action.
    4396             :  *
    4397             :  * While these operations do not operate entirely within the bounds of
    4398             :  * snapshot isolation, they can occur inside a serializable transaction, and
    4399             :  * will logically occur after any reads which saw rows which were destroyed
    4400             :  * by these operations, so we do what we can to serialize properly under
    4401             :  * SSI.
    4402             :  *
    4403             :  * The relation passed in must be a heap relation. Any predicate lock of any
    4404             :  * granularity on the heap will cause a rw-conflict in to this transaction.
    4405             :  * Predicate locks on indexes do not matter because they only exist to guard
    4406             :  * against conflicting inserts into the index, and this is a mass *delete*.
    4407             :  * When a table is truncated or dropped, the index will also be truncated
    4408             :  * or dropped, and we'll deal with locks on the index when that happens.
    4409             :  *
    4410             :  * Dropping or truncating a table also needs to drop any existing predicate
    4411             :  * locks on heap tuples or pages, because they're about to go away. This
    4412             :  * should be done before altering the predicate locks because the transaction
    4413             :  * could be rolled back because of a conflict, in which case the lock changes
    4414             :  * are not needed. (At the moment, we don't actually bother to drop the
    4415             :  * existing locks on a dropped or truncated table at the moment. That might
    4416             :  * lead to some false positives, but it doesn't seem worth the trouble.)
    4417             :  */
    4418             : void
    4419       51906 : CheckTableForSerializableConflictIn(Relation relation)
    4420             : {
    4421             :     HASH_SEQ_STATUS seqstat;
    4422             :     PREDICATELOCKTARGET *target;
    4423             :     Oid         dbId;
    4424             :     Oid         heapId;
    4425             :     int         i;
    4426             : 
    4427             :     /*
    4428             :      * Bail out quickly if there are no serializable transactions running.
    4429             :      * It's safe to check this without taking locks because the caller is
    4430             :      * holding an ACCESS EXCLUSIVE lock on the relation.  No new locks which
    4431             :      * would matter here can be acquired while that is held.
    4432             :      */
    4433       51906 :     if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
    4434       51900 :         return;
    4435             : 
    4436         282 :     if (!SerializationNeededForWrite(relation))
    4437         276 :         return;
    4438             : 
    4439             :     /*
    4440             :      * We're doing a write which might cause rw-conflicts now or later.
    4441             :      * Memorize that fact.
    4442             :      */
    4443           6 :     MyXactDidWrite = true;
    4444             : 
    4445             :     Assert(relation->rd_index == NULL); /* not an index relation */
    4446             : 
    4447           6 :     dbId = relation->rd_locator.dbOid;
    4448           6 :     heapId = relation->rd_id;
    4449             : 
    4450           6 :     LWLockAcquire(SerializablePredicateListLock, LW_EXCLUSIVE);
    4451         102 :     for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
    4452          96 :         LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_SHARED);
    4453           6 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4454             : 
    4455             :     /* Scan through target list */
    4456           6 :     hash_seq_init(&seqstat, PredicateLockTargetHash);
    4457             : 
    4458          12 :     while ((target = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat)))
    4459             :     {
    4460             :         dlist_mutable_iter iter;
    4461             : 
    4462             :         /*
    4463             :          * Check whether this is a target which needs attention.
    4464             :          */
    4465           6 :         if (GET_PREDICATELOCKTARGETTAG_RELATION(target->tag) != heapId)
    4466           6 :             continue;           /* wrong relation id */
    4467           0 :         if (GET_PREDICATELOCKTARGETTAG_DB(target->tag) != dbId)
    4468           0 :             continue;           /* wrong database id */
    4469             : 
    4470             :         /*
    4471             :          * Loop through locks for this target and flag conflicts.
    4472             :          */
    4473           0 :         dlist_foreach_modify(iter, &target->predicateLocks)
    4474             :         {
    4475           0 :             PREDICATELOCK *predlock =
    4476           0 :                 dlist_container(PREDICATELOCK, targetLink, iter.cur);
    4477             : 
    4478           0 :             if (predlock->tag.myXact != MySerializableXact
    4479           0 :                 && !RWConflictExists(predlock->tag.myXact, MySerializableXact))
    4480             :             {
    4481           0 :                 FlagRWConflict(predlock->tag.myXact, MySerializableXact);
    4482             :             }
    4483             :         }
    4484             :     }
    4485             : 
    4486             :     /* Release locks in reverse order */
    4487           6 :     LWLockRelease(SerializableXactHashLock);
    4488         102 :     for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
    4489          96 :         LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
    4490           6 :     LWLockRelease(SerializablePredicateListLock);
    4491             : }
    4492             : 
    4493             : 
    4494             : /*
    4495             :  * Flag a rw-dependency between two serializable transactions.
    4496             :  *
    4497             :  * The caller is responsible for ensuring that we have a LW lock on
    4498             :  * the transaction hash table.
    4499             :  */
    4500             : static void
    4501        1720 : FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer)
    4502             : {
    4503             :     Assert(reader != writer);
    4504             : 
    4505             :     /* First, see if this conflict causes failure. */
    4506        1720 :     OnConflict_CheckForSerializationFailure(reader, writer);
    4507             : 
    4508             :     /* Actually do the conflict flagging. */
    4509        1560 :     if (reader == OldCommittedSxact)
    4510           0 :         writer->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
    4511        1560 :     else if (writer == OldCommittedSxact)
    4512           0 :         reader->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
    4513             :     else
    4514        1560 :         SetRWConflict(reader, writer);
    4515        1560 : }
    4516             : 
    4517             : /*----------------------------------------------------------------------------
    4518             :  * We are about to add a RW-edge to the dependency graph - check that we don't
    4519             :  * introduce a dangerous structure by doing so, and abort one of the
    4520             :  * transactions if so.
    4521             :  *
    4522             :  * A serialization failure can only occur if there is a dangerous structure
    4523             :  * in the dependency graph:
    4524             :  *
    4525             :  *      Tin ------> Tpivot ------> Tout
    4526             :  *            rw             rw
    4527             :  *
    4528             :  * Furthermore, Tout must commit first.
    4529             :  *
    4530             :  * One more optimization is that if Tin is declared READ ONLY (or commits
    4531             :  * without writing), we can only have a problem if Tout committed before Tin
    4532             :  * acquired its snapshot.
    4533             :  *----------------------------------------------------------------------------
    4534             :  */
    4535             : static void
    4536        1720 : OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
    4537             :                                         SERIALIZABLEXACT *writer)
    4538             : {
    4539             :     bool        failure;
    4540             : 
    4541             :     Assert(LWLockHeldByMe(SerializableXactHashLock));
    4542             : 
    4543        1720 :     failure = false;
    4544             : 
    4545             :     /*------------------------------------------------------------------------
    4546             :      * Check for already-committed writer with rw-conflict out flagged
    4547             :      * (conflict-flag on W means that T2 committed before W):
    4548             :      *
    4549             :      *      R ------> W ------> T2
    4550             :      *          rw        rw
    4551             :      *
    4552             :      * That is a dangerous structure, so we must abort. (Since the writer
    4553             :      * has already committed, we must be the reader)
    4554             :      *------------------------------------------------------------------------
    4555             :      */
    4556        1720 :     if (SxactIsCommitted(writer)
    4557          36 :         && (SxactHasConflictOut(writer) || SxactHasSummaryConflictOut(writer)))
    4558           4 :         failure = true;
    4559             : 
    4560             :     /*------------------------------------------------------------------------
    4561             :      * Check whether the writer has become a pivot with an out-conflict
    4562             :      * committed transaction (T2), and T2 committed first:
    4563             :      *
    4564             :      *      R ------> W ------> T2
    4565             :      *          rw        rw
    4566             :      *
    4567             :      * Because T2 must've committed first, there is no anomaly if:
    4568             :      * - the reader committed before T2
    4569             :      * - the writer committed before T2
    4570             :      * - the reader is a READ ONLY transaction and the reader was concurrent
    4571             :      *   with T2 (= reader acquired its snapshot before T2 committed)
    4572             :      *
    4573             :      * We also handle the case that T2 is prepared but not yet committed
    4574             :      * here. In that case T2 has already checked for conflicts, so if it
    4575             :      * commits first, making the above conflict real, it's too late for it
    4576             :      * to abort.
    4577             :      *------------------------------------------------------------------------
    4578             :      */
    4579        1720 :     if (!failure && SxactHasSummaryConflictOut(writer))
    4580           0 :         failure = true;
    4581        1720 :     else if (!failure)
    4582             :     {
    4583             :         dlist_iter  iter;
    4584             : 
    4585        2142 :         dlist_foreach(iter, &writer->outConflicts)
    4586             :         {
    4587         576 :             RWConflict  conflict =
    4588         576 :                 dlist_container(RWConflictData, outLink, iter.cur);
    4589         576 :             SERIALIZABLEXACT *t2 = conflict->sxactIn;
    4590             : 
    4591         576 :             if (SxactIsPrepared(t2)
    4592         162 :                 && (!SxactIsCommitted(reader)
    4593         130 :                     || t2->prepareSeqNo <= reader->commitSeqNo)
    4594         162 :                 && (!SxactIsCommitted(writer)
    4595           0 :                     || t2->prepareSeqNo <= writer->commitSeqNo)
    4596         162 :                 && (!SxactIsReadOnly(reader)
    4597          24 :                     || t2->prepareSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))
    4598             :             {
    4599         150 :                 failure = true;
    4600         150 :                 break;
    4601             :             }
    4602             :         }
    4603             :     }
    4604             : 
    4605             :     /*------------------------------------------------------------------------
    4606             :      * Check whether the reader has become a pivot with a writer
    4607             :      * that's committed (or prepared):
    4608             :      *
    4609             :      *      T0 ------> R ------> W
    4610             :      *           rw        rw
    4611             :      *
    4612             :      * Because W must've committed first for an anomaly to occur, there is no
    4613             :      * anomaly if:
    4614             :      * - T0 committed before the writer
    4615             :      * - T0 is READ ONLY, and overlaps the writer
    4616             :      *------------------------------------------------------------------------
    4617             :      */
    4618        1720 :     if (!failure && SxactIsPrepared(writer) && !SxactIsReadOnly(reader))
    4619             :     {
    4620          36 :         if (SxactHasSummaryConflictIn(reader))
    4621             :         {
    4622           0 :             failure = true;
    4623             :         }
    4624             :         else
    4625             :         {
    4626             :             dlist_iter  iter;
    4627             : 
    4628             :             /*
    4629             :              * The unconstify is needed as we have no const version of
    4630             :              * dlist_foreach().
    4631             :              */
    4632          36 :             dlist_foreach(iter, &unconstify(SERIALIZABLEXACT *, reader)->inConflicts)
    4633             :             {
    4634          22 :                 const RWConflict conflict =
    4635          22 :                     dlist_container(RWConflictData, inLink, iter.cur);
    4636          22 :                 const SERIALIZABLEXACT *t0 = conflict->sxactOut;
    4637             : 
    4638          22 :                 if (!SxactIsDoomed(t0)
    4639          22 :                     && (!SxactIsCommitted(t0)
    4640          22 :                         || t0->commitSeqNo >= writer->prepareSeqNo)
    4641          22 :                     && (!SxactIsReadOnly(t0)
    4642           0 :                         || t0->SeqNo.lastCommitBeforeSnapshot >= writer->prepareSeqNo))
    4643             :                 {
    4644          22 :                     failure = true;
    4645          22 :                     break;
    4646             :                 }
    4647             :             }
    4648             :         }
    4649             :     }
    4650             : 
    4651        1720 :     if (failure)
    4652             :     {
    4653             :         /*
    4654             :          * We have to kill a transaction to avoid a possible anomaly from
    4655             :          * occurring. If the writer is us, we can just ereport() to cause a
    4656             :          * transaction abort. Otherwise we flag the writer for termination,
    4657             :          * causing it to abort when it tries to commit. However, if the writer
    4658             :          * is a prepared transaction, already prepared, we can't abort it
    4659             :          * anymore, so we have to kill the reader instead.
    4660             :          */
    4661         176 :         if (MySerializableXact == writer)
    4662             :         {
    4663         134 :             LWLockRelease(SerializableXactHashLock);
    4664         134 :             ereport(ERROR,
    4665             :                     (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4666             :                      errmsg("could not serialize access due to read/write dependencies among transactions"),
    4667             :                      errdetail_internal("Reason code: Canceled on identification as a pivot, during write."),
    4668             :                      errhint("The transaction might succeed if retried.")));
    4669             :         }
    4670          42 :         else if (SxactIsPrepared(writer))
    4671             :         {
    4672          26 :             LWLockRelease(SerializableXactHashLock);
    4673             : 
    4674             :             /* if we're not the writer, we have to be the reader */
    4675             :             Assert(MySerializableXact == reader);
    4676          26 :             ereport(ERROR,
    4677             :                     (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4678             :                      errmsg("could not serialize access due to read/write dependencies among transactions"),
    4679             :                      errdetail_internal("Reason code: Canceled on conflict out to pivot %u, during read.", writer->topXid),
    4680             :                      errhint("The transaction might succeed if retried.")));
    4681             :         }
    4682          16 :         writer->flags |= SXACT_FLAG_DOOMED;
    4683             :     }
    4684        1560 : }
    4685             : 
    4686             : /*
    4687             :  * PreCommit_CheckForSerializationFailure
    4688             :  *      Check for dangerous structures in a serializable transaction
    4689             :  *      at commit.
    4690             :  *
    4691             :  * We're checking for a dangerous structure as each conflict is recorded.
    4692             :  * The only way we could have a problem at commit is if this is the "out"
    4693             :  * side of a pivot, and neither the "in" side nor the pivot has yet
    4694             :  * committed.
    4695             :  *
    4696             :  * If a dangerous structure is found, the pivot (the near conflict) is
    4697             :  * marked for death, because rolling back another transaction might mean
    4698             :  * that we fail without ever making progress.  This transaction is
    4699             :  * committing writes, so letting it commit ensures progress.  If we
    4700             :  * canceled the far conflict, it might immediately fail again on retry.
    4701             :  */
    4702             : void
    4703      815090 : PreCommit_CheckForSerializationFailure(void)
    4704             : {
    4705             :     dlist_iter  near_iter;
    4706             : 
    4707      815090 :     if (MySerializableXact == InvalidSerializableXact)
    4708      812326 :         return;
    4709             : 
    4710             :     Assert(IsolationIsSerializable());
    4711             : 
    4712        2764 :     LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4713             : 
    4714             :     /*
    4715             :      * Check if someone else has already decided that we need to die.  Since
    4716             :      * we set our own DOOMED flag when partially releasing, ignore in that
    4717             :      * case.
    4718             :      */
    4719        2764 :     if (SxactIsDoomed(MySerializableXact) &&
    4720         312 :         !SxactIsPartiallyReleased(MySerializableXact))
    4721             :     {
    4722         310 :         LWLockRelease(SerializableXactHashLock);
    4723         310 :         ereport(ERROR,
    4724             :                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4725             :                  errmsg("could not serialize access due to read/write dependencies among transactions"),
    4726             :                  errdetail_internal("Reason code: Canceled on identification as a pivot, during commit attempt."),
    4727             :                  errhint("The transaction might succeed if retried.")));
    4728             :     }
    4729             : 
    4730        3656 :     dlist_foreach(near_iter, &MySerializableXact->inConflicts)
    4731             :     {
    4732        1202 :         RWConflict  nearConflict =
    4733        1202 :             dlist_container(RWConflictData, inLink, near_iter.cur);
    4734             : 
    4735        1202 :         if (!SxactIsCommitted(nearConflict->sxactOut)
    4736         834 :             && !SxactIsDoomed(nearConflict->sxactOut))
    4737             :         {
    4738             :             dlist_iter  far_iter;
    4739             : 
    4740         894 :             dlist_foreach(far_iter, &nearConflict->sxactOut->inConflicts)
    4741             :             {
    4742         356 :                 RWConflict  farConflict =
    4743         356 :                     dlist_container(RWConflictData, inLink, far_iter.cur);
    4744             : 
    4745         356 :                 if (farConflict->sxactOut == MySerializableXact
    4746          84 :                     || (!SxactIsCommitted(farConflict->sxactOut)
    4747          48 :                         && !SxactIsReadOnly(farConflict->sxactOut)
    4748          24 :                         && !SxactIsDoomed(farConflict->sxactOut)))
    4749             :                 {
    4750             :                     /*
    4751             :                      * Normally, we kill the pivot transaction to make sure we
    4752             :                      * make progress if the failing transaction is retried.
    4753             :                      * However, we can't kill it if it's already prepared, so
    4754             :                      * in that case we commit suicide instead.
    4755             :                      */
    4756         296 :                     if (SxactIsPrepared(nearConflict->sxactOut))
    4757             :                     {
    4758           0 :                         LWLockRelease(SerializableXactHashLock);
    4759           0 :                         ereport(ERROR,
    4760             :                                 (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
    4761             :                                  errmsg("could not serialize access due to read/write dependencies among transactions"),
    4762             :                                  errdetail_internal("Reason code: Canceled on commit attempt with conflict in from prepared pivot."),
    4763             :                                  errhint("The transaction might succeed if retried.")));
    4764             :                     }
    4765         296 :                     nearConflict->sxactOut->flags |= SXACT_FLAG_DOOMED;
    4766         296 :                     break;
    4767             :                 }
    4768             :             }
    4769             :         }
    4770             :     }
    4771             : 
    4772        2454 :     MySerializableXact->prepareSeqNo = ++(PredXact->LastSxactCommitSeqNo);
    4773        2454 :     MySerializableXact->flags |= SXACT_FLAG_PREPARED;
    4774             : 
    4775        2454 :     LWLockRelease(SerializableXactHashLock);
    4776             : }
    4777             : 
    4778             : /*------------------------------------------------------------------------*/
    4779             : 
    4780             : /*
    4781             :  * Two-phase commit support
    4782             :  */
    4783             : 
    4784             : /*
    4785             :  * AtPrepare_Locks
    4786             :  *      Do the preparatory work for a PREPARE: make 2PC state file
    4787             :  *      records for all predicate locks currently held.
    4788             :  */
    4789             : void
    4790         562 : AtPrepare_PredicateLocks(void)
    4791             : {
    4792             :     SERIALIZABLEXACT *sxact;
    4793             :     TwoPhasePredicateRecord record;
    4794             :     TwoPhasePredicateXactRecord *xactRecord;
    4795             :     TwoPhasePredicateLockRecord *lockRecord;
    4796             :     dlist_iter  iter;
    4797             : 
    4798         562 :     sxact = MySerializableXact;
    4799         562 :     xactRecord = &(record.data.xactRecord);
    4800         562 :     lockRecord = &(record.data.lockRecord);
    4801             : 
    4802         562 :     if (MySerializableXact == InvalidSerializableXact)
    4803         538 :         return;
    4804             : 
    4805             :     /* Generate an xact record for our SERIALIZABLEXACT */
    4806          24 :     record.type = TWOPHASEPREDICATERECORD_XACT;
    4807          24 :     xactRecord->xmin = MySerializableXact->xmin;
    4808          24 :     xactRecord->flags = MySerializableXact->flags;
    4809             : 
    4810             :     /*
    4811             :      * Note that we don't include the list of conflicts in our out in the
    4812             :      * statefile, because new conflicts can be added even after the
    4813             :      * transaction prepares. We'll just make a conservative assumption during
    4814             :      * recovery instead.
    4815             :      */
    4816             : 
    4817          24 :     RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0,
    4818             :                            &record, sizeof(record));
    4819             : 
    4820             :     /*
    4821             :      * Generate a lock record for each lock.
    4822             :      *
    4823             :      * To do this, we need to walk the predicate lock list in our sxact rather
    4824             :      * than using the local predicate lock table because the latter is not
    4825             :      * guaranteed to be accurate.
    4826             :      */
    4827          24 :     LWLockAcquire(SerializablePredicateListLock, LW_SHARED);
    4828             : 
    4829             :     /*
    4830             :      * No need to take sxact->perXactPredicateListLock in parallel mode
    4831             :      * because there cannot be any parallel workers running while we are
    4832             :      * preparing a transaction.
    4833             :      */
    4834             :     Assert(!IsParallelWorker() && !ParallelContextActive());
    4835             : 
    4836          44 :     dlist_foreach(iter, &sxact->predicateLocks)
    4837             :     {
    4838          20 :         PREDICATELOCK *predlock =
    4839          20 :             dlist_container(PREDICATELOCK, xactLink, iter.cur);
    4840             : 
    4841          20 :         record.type = TWOPHASEPREDICATERECORD_LOCK;
    4842          20 :         lockRecord->target = predlock->tag.myTarget->tag;
    4843             : 
    4844          20 :         RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0,
    4845             :                                &record, sizeof(record));
    4846             :     }
    4847             : 
    4848          24 :     LWLockRelease(SerializablePredicateListLock);
    4849             : }
    4850             : 
    4851             : /*
    4852             :  * PostPrepare_Locks
    4853             :  *      Clean up after successful PREPARE. Unlike the non-predicate
    4854             :  *      lock manager, we do not need to transfer locks to a dummy
    4855             :  *      PGPROC because our SERIALIZABLEXACT will stay around
    4856             :  *      anyway. We only need to clean up our local state.
    4857             :  */
    4858             : void
    4859         562 : PostPrepare_PredicateLocks(TransactionId xid)
    4860             : {
    4861         562 :     if (MySerializableXact == InvalidSerializableXact)
    4862         538 :         return;
    4863             : 
    4864             :     Assert(SxactIsPrepared(MySerializableXact));
    4865             : 
    4866          24 :     MySerializableXact->pid = 0;
    4867          24 :     MySerializableXact->pgprocno = INVALID_PROC_NUMBER;
    4868             : 
    4869          24 :     hash_destroy(LocalPredicateLockHash);
    4870          24 :     LocalPredicateLockHash = NULL;
    4871             : 
    4872          24 :     MySerializableXact = InvalidSerializableXact;
    4873          24 :     MyXactDidWrite = false;
    4874             : }
    4875             : 
    4876             : /*
    4877             :  * PredicateLockTwoPhaseFinish
    4878             :  *      Release a prepared transaction's predicate locks once it
    4879             :  *      commits or aborts.
    4880             :  */
    4881             : void
    4882         570 : PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit)
    4883             : {
    4884             :     SERIALIZABLEXID *sxid;
    4885             :     SERIALIZABLEXIDTAG sxidtag;
    4886             : 
    4887         570 :     sxidtag.xid = xid;
    4888             : 
    4889         570 :     LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    4890             :     sxid = (SERIALIZABLEXID *)
    4891         570 :         hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
    4892         570 :     LWLockRelease(SerializableXactHashLock);
    4893             : 
    4894             :     /* xid will not be found if it wasn't a serializable transaction */
    4895         570 :     if (sxid == NULL)
    4896         546 :         return;
    4897             : 
    4898             :     /* Release its locks */
    4899          24 :     MySerializableXact = sxid->myXact;
    4900          24 :     MyXactDidWrite = true;      /* conservatively assume that we wrote
    4901             :                                  * something */
    4902          24 :     ReleasePredicateLocks(isCommit, false);
    4903             : }
    4904             : 
    4905             : /*
    4906             :  * Re-acquire a predicate lock belonging to a transaction that was prepared.
    4907             :  */
    4908             : void
    4909           0 : predicatelock_twophase_recover(TransactionId xid, uint16 info,
    4910             :                                void *recdata, uint32 len)
    4911             : {
    4912             :     TwoPhasePredicateRecord *record;
    4913             : 
    4914             :     Assert(len == sizeof(TwoPhasePredicateRecord));
    4915             : 
    4916           0 :     record = (TwoPhasePredicateRecord *) recdata;
    4917             : 
    4918             :     Assert((record->type == TWOPHASEPREDICATERECORD_XACT) ||
    4919             :            (record->type == TWOPHASEPREDICATERECORD_LOCK));
    4920             : 
    4921           0 :     if (record->type == TWOPHASEPREDICATERECORD_XACT)
    4922             :     {
    4923             :         /* Per-transaction record. Set up a SERIALIZABLEXACT. */
    4924             :         TwoPhasePredicateXactRecord *xactRecord;
    4925             :         SERIALIZABLEXACT *sxact;
    4926             :         SERIALIZABLEXID *sxid;
    4927             :         SERIALIZABLEXIDTAG sxidtag;
    4928             :         bool        found;
    4929             : 
    4930           0 :         xactRecord = (TwoPhasePredicateXactRecord *) &record->data.xactRecord;
    4931             : 
    4932           0 :         LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
    4933           0 :         sxact = CreatePredXact();
    4934           0 :         if (!sxact)
    4935           0 :             ereport(ERROR,
    4936             :                     (errcode(ERRCODE_OUT_OF_MEMORY),
    4937             :                      errmsg("out of shared memory")));
    4938             : 
    4939             :         /* vxid for a prepared xact is INVALID_PROC_NUMBER/xid; no pid */
    4940           0 :         sxact->vxid.procNumber = INVALID_PROC_NUMBER;
    4941           0 :         sxact->vxid.localTransactionId = (LocalTransactionId) xid;
    4942           0 :         sxact->pid = 0;
    4943           0 :         sxact->pgprocno = INVALID_PROC_NUMBER;
    4944             : 
    4945             :         /* a prepared xact hasn't committed yet */
    4946           0 :         sxact->prepareSeqNo = RecoverySerCommitSeqNo;
    4947           0 :         sxact->commitSeqNo = InvalidSerCommitSeqNo;
    4948           0 :         sxact->finishedBefore = InvalidTransactionId;
    4949             : 
    4950           0 :         sxact->SeqNo.lastCommitBeforeSnapshot = RecoverySerCommitSeqNo;
    4951             : 
    4952             :         /*
    4953             :          * Don't need to track this; no transactions running at the time the
    4954             :          * recovered xact started are still active, except possibly other
    4955             :          * prepared xacts and we don't care whether those are RO_SAFE or not.
    4956             :          */
    4957           0 :         dlist_init(&(sxact->possibleUnsafeConflicts));
    4958             : 
    4959           0 :         dlist_init(&(sxact->predicateLocks));
    4960           0 :         dlist_node_init(&sxact->finishedLink);
    4961             : 
    4962           0 :         sxact->topXid = xid;
    4963           0 :         sxact->xmin = xactRecord->xmin;
    4964           0 :         sxact->flags = xactRecord->flags;
    4965             :         Assert(SxactIsPrepared(sxact));
    4966           0 :         if (!SxactIsReadOnly(sxact))
    4967             :         {
    4968           0 :             ++(PredXact->WritableSxactCount);
    4969             :             Assert(PredXact->WritableSxactCount <=
    4970             :                    (MaxBackends + max_prepared_xacts));
    4971             :         }
    4972             : 
    4973             :         /*
    4974             :          * We don't know whether the transaction had any conflicts or not, so
    4975             :          * we'll conservatively assume that it had both a conflict in and a
    4976             :          * conflict out, and represent that with the summary conflict flags.
    4977             :          */
    4978           0 :         dlist_init(&(sxact->outConflicts));
    4979           0 :         dlist_init(&(sxact->inConflicts));
    4980           0 :         sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
    4981           0 :         sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
    4982             : 
    4983             :         /* Register the transaction's xid */
    4984           0 :         sxidtag.xid = xid;
    4985           0 :         sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash,
    4986             :                                                &sxidtag,
    4987             :                                                HASH_ENTER, &found);
    4988             :         Assert(sxid != NULL);
    4989             :         Assert(!found);
    4990           0 :         sxid->myXact = (SERIALIZABLEXACT *) sxact;
    4991             : 
    4992             :         /*
    4993             :          * Update global xmin. Note that this is a special case compared to
    4994             :          * registering a normal transaction, because the global xmin might go
    4995             :          * backwards. That's OK, because until recovery is over we're not
    4996             :          * going to complete any transactions or create any non-prepared
    4997             :          * transactions, so there's no danger of throwing away.
    4998             :          */
    4999           0 :         if ((!TransactionIdIsValid(PredXact->SxactGlobalXmin)) ||
    5000           0 :             (TransactionIdFollows(PredXact->SxactGlobalXmin, sxact->xmin)))
    5001             :         {
    5002           0 :             PredXact->SxactGlobalXmin = sxact->xmin;
    5003           0 :             PredXact->SxactGlobalXminCount = 1;
    5004           0 :             SerialSetActiveSerXmin(sxact->xmin);
    5005             :         }
    5006           0 :         else if (TransactionIdEquals(sxact->xmin, PredXact->SxactGlobalXmin))
    5007             :         {
    5008             :             Assert(PredXact->SxactGlobalXminCount > 0);
    5009           0 :             PredXact->SxactGlobalXminCount++;
    5010             :         }
    5011             : 
    5012           0 :         LWLockRelease(SerializableXactHashLock);
    5013             :     }
    5014           0 :     else if (record->type == TWOPHASEPREDICATERECORD_LOCK)
    5015             :     {
    5016             :         /* Lock record. Recreate the PREDICATELOCK */
    5017             :         TwoPhasePredicateLockRecord *lockRecord;
    5018             :         SERIALIZABLEXID *sxid;
    5019             :         SERIALIZABLEXACT *sxact;
    5020             :         SERIALIZABLEXIDTAG sxidtag;
    5021             :         uint32      targettaghash;
    5022             : 
    5023           0 :         lockRecord = (TwoPhasePredicateLockRecord *) &record->data.lockRecord;
    5024           0 :         targettaghash = PredicateLockTargetTagHashCode(&lockRecord->target);
    5025             : 
    5026           0 :         LWLockAcquire(SerializableXactHashLock, LW_SHARED);
    5027           0 :         sxidtag.xid = xid;
    5028             :         sxid = (SERIALIZABLEXID *)
    5029           0 :             hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
    5030           0 :         LWLockRelease(SerializableXactHashLock);
    5031             : 
    5032             :         Assert(sxid != NULL);
    5033           0 :         sxact = sxid->myXact;
    5034             :         Assert(sxact != InvalidSerializableXact);
    5035             : 
    5036           0 :         CreatePredicateLock(&lockRecord->target, targettaghash, sxact);
    5037             :     }
    5038           0 : }
    5039             : 
    5040             : /*
    5041             :  * Prepare to share the current SERIALIZABLEXACT with parallel workers.
    5042             :  * Return a handle object that can be used by AttachSerializableXact() in a
    5043             :  * parallel worker.
    5044             :  */
    5045             : SerializableXactHandle
    5046         910 : ShareSerializableXact(void)
    5047             : {
    5048         910 :     return MySerializableXact;
    5049             : }
    5050             : 
    5051             : /*
    5052             :  * Allow parallel workers to import the leader's SERIALIZABLEXACT.
    5053             :  */
    5054             : void
    5055        2740 : AttachSerializableXact(SerializableXactHandle handle)
    5056             : {
    5057             : 
    5058             :     Assert(MySerializableXact == InvalidSerializableXact);
    5059             : 
    5060        2740 :     MySerializableXact = (SERIALIZABLEXACT *) handle;
    5061        2740 :     if (MySerializableXact != InvalidSerializableXact)
    5062          26 :         CreateLocalPredicateLockHash();
    5063        2740 : }

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