LCOV - code coverage report
Current view: top level - src/backend/postmaster - checkpointer.c (source / functions) Hit Total Coverage
Test: PostgreSQL 19devel Lines: 330 382 86.4 %
Date: 2025-07-20 00:17:26 Functions: 16 16 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * checkpointer.c
       4             :  *
       5             :  * The checkpointer is new as of Postgres 9.2.  It handles all checkpoints.
       6             :  * Checkpoints are automatically dispatched after a certain amount of time has
       7             :  * elapsed since the last one, and it can be signaled to perform requested
       8             :  * checkpoints as well.  (The GUC parameter that mandates a checkpoint every
       9             :  * so many WAL segments is implemented by having backends signal when they
      10             :  * fill WAL segments; the checkpointer itself doesn't watch for the
      11             :  * condition.)
      12             :  *
      13             :  * The normal termination sequence is that checkpointer is instructed to
      14             :  * execute the shutdown checkpoint by SIGINT.  After that checkpointer waits
      15             :  * to be terminated via SIGUSR2, which instructs the checkpointer to exit(0).
      16             :  * All backends must be stopped before SIGINT or SIGUSR2 is issued!
      17             :  *
      18             :  * Emergency termination is by SIGQUIT; like any backend, the checkpointer
      19             :  * will simply abort and exit on SIGQUIT.
      20             :  *
      21             :  * If the checkpointer exits unexpectedly, the postmaster treats that the same
      22             :  * as a backend crash: shared memory may be corrupted, so remaining backends
      23             :  * should be killed by SIGQUIT and then a recovery cycle started.  (Even if
      24             :  * shared memory isn't corrupted, we have lost information about which
      25             :  * files need to be fsync'd for the next checkpoint, and so a system
      26             :  * restart needs to be forced.)
      27             :  *
      28             :  *
      29             :  * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
      30             :  *
      31             :  *
      32             :  * IDENTIFICATION
      33             :  *    src/backend/postmaster/checkpointer.c
      34             :  *
      35             :  *-------------------------------------------------------------------------
      36             :  */
      37             : #include "postgres.h"
      38             : 
      39             : #include <sys/time.h>
      40             : #include <time.h>
      41             : 
      42             : #include "access/xlog.h"
      43             : #include "access/xlog_internal.h"
      44             : #include "access/xlogrecovery.h"
      45             : #include "catalog/pg_authid.h"
      46             : #include "commands/defrem.h"
      47             : #include "libpq/pqsignal.h"
      48             : #include "miscadmin.h"
      49             : #include "pgstat.h"
      50             : #include "postmaster/auxprocess.h"
      51             : #include "postmaster/bgwriter.h"
      52             : #include "postmaster/interrupt.h"
      53             : #include "replication/syncrep.h"
      54             : #include "storage/aio_subsys.h"
      55             : #include "storage/bufmgr.h"
      56             : #include "storage/condition_variable.h"
      57             : #include "storage/fd.h"
      58             : #include "storage/ipc.h"
      59             : #include "storage/lwlock.h"
      60             : #include "storage/pmsignal.h"
      61             : #include "storage/proc.h"
      62             : #include "storage/procsignal.h"
      63             : #include "storage/shmem.h"
      64             : #include "storage/smgr.h"
      65             : #include "storage/spin.h"
      66             : #include "utils/acl.h"
      67             : #include "utils/guc.h"
      68             : #include "utils/memutils.h"
      69             : #include "utils/resowner.h"
      70             : 
      71             : 
      72             : /*----------
      73             :  * Shared memory area for communication between checkpointer and backends
      74             :  *
      75             :  * The ckpt counters allow backends to watch for completion of a checkpoint
      76             :  * request they send.  Here's how it works:
      77             :  *  * At start of a checkpoint, checkpointer reads (and clears) the request
      78             :  *    flags and increments ckpt_started, while holding ckpt_lck.
      79             :  *  * On completion of a checkpoint, checkpointer sets ckpt_done to
      80             :  *    equal ckpt_started.
      81             :  *  * On failure of a checkpoint, checkpointer increments ckpt_failed
      82             :  *    and sets ckpt_done to equal ckpt_started.
      83             :  *
      84             :  * The algorithm for backends is:
      85             :  *  1. Record current values of ckpt_failed and ckpt_started, and
      86             :  *     set request flags, while holding ckpt_lck.
      87             :  *  2. Send signal to request checkpoint.
      88             :  *  3. Sleep until ckpt_started changes.  Now you know a checkpoint has
      89             :  *     begun since you started this algorithm (although *not* that it was
      90             :  *     specifically initiated by your signal), and that it is using your flags.
      91             :  *  4. Record new value of ckpt_started.
      92             :  *  5. Sleep until ckpt_done >= saved value of ckpt_started.  (Use modulo
      93             :  *     arithmetic here in case counters wrap around.)  Now you know a
      94             :  *     checkpoint has started and completed, but not whether it was
      95             :  *     successful.
      96             :  *  6. If ckpt_failed is different from the originally saved value,
      97             :  *     assume request failed; otherwise it was definitely successful.
      98             :  *
      99             :  * ckpt_flags holds the OR of the checkpoint request flags sent by all
     100             :  * requesting backends since the last checkpoint start.  The flags are
     101             :  * chosen so that OR'ing is the correct way to combine multiple requests.
     102             :  *
     103             :  * The requests array holds fsync requests sent by backends and not yet
     104             :  * absorbed by the checkpointer.
     105             :  *
     106             :  * Unlike the checkpoint fields, requests related fields are protected by
     107             :  * CheckpointerCommLock.
     108             :  *----------
     109             :  */
     110             : typedef struct
     111             : {
     112             :     SyncRequestType type;       /* request type */
     113             :     FileTag     ftag;           /* file identifier */
     114             : } CheckpointerRequest;
     115             : 
     116             : typedef struct
     117             : {
     118             :     pid_t       checkpointer_pid;   /* PID (0 if not started) */
     119             : 
     120             :     slock_t     ckpt_lck;       /* protects all the ckpt_* fields */
     121             : 
     122             :     int         ckpt_started;   /* advances when checkpoint starts */
     123             :     int         ckpt_done;      /* advances when checkpoint done */
     124             :     int         ckpt_failed;    /* advances when checkpoint fails */
     125             : 
     126             :     int         ckpt_flags;     /* checkpoint flags, as defined in xlog.h */
     127             : 
     128             :     ConditionVariable start_cv; /* signaled when ckpt_started advances */
     129             :     ConditionVariable done_cv;  /* signaled when ckpt_done advances */
     130             : 
     131             :     int         num_requests;   /* current # of requests */
     132             :     int         max_requests;   /* allocated array size */
     133             :     CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
     134             : } CheckpointerShmemStruct;
     135             : 
     136             : static CheckpointerShmemStruct *CheckpointerShmem;
     137             : 
     138             : /* interval for calling AbsorbSyncRequests in CheckpointWriteDelay */
     139             : #define WRITES_PER_ABSORB       1000
     140             : 
     141             : /*
     142             :  * GUC parameters
     143             :  */
     144             : int         CheckPointTimeout = 300;
     145             : int         CheckPointWarning = 30;
     146             : double      CheckPointCompletionTarget = 0.9;
     147             : 
     148             : /*
     149             :  * Private state
     150             :  */
     151             : static bool ckpt_active = false;
     152             : static volatile sig_atomic_t ShutdownXLOGPending = false;
     153             : 
     154             : /* these values are valid when ckpt_active is true: */
     155             : static pg_time_t ckpt_start_time;
     156             : static XLogRecPtr ckpt_start_recptr;
     157             : static double ckpt_cached_elapsed;
     158             : 
     159             : static pg_time_t last_checkpoint_time;
     160             : static pg_time_t last_xlog_switch_time;
     161             : 
     162             : /* Prototypes for private functions */
     163             : 
     164             : static void ProcessCheckpointerInterrupts(void);
     165             : static void CheckArchiveTimeout(void);
     166             : static bool IsCheckpointOnSchedule(double progress);
     167             : static bool FastCheckpointRequested(void);
     168             : static bool CompactCheckpointerRequestQueue(void);
     169             : static void UpdateSharedMemoryConfig(void);
     170             : 
     171             : /* Signal handlers */
     172             : static void ReqShutdownXLOG(SIGNAL_ARGS);
     173             : 
     174             : 
     175             : /*
     176             :  * Main entry point for checkpointer process
     177             :  *
     178             :  * This is invoked from AuxiliaryProcessMain, which has already created the
     179             :  * basic execution environment, but not enabled signals yet.
     180             :  */
     181             : void
     182        1026 : CheckpointerMain(const void *startup_data, size_t startup_data_len)
     183             : {
     184             :     sigjmp_buf  local_sigjmp_buf;
     185             :     MemoryContext checkpointer_context;
     186             : 
     187             :     Assert(startup_data_len == 0);
     188             : 
     189        1026 :     MyBackendType = B_CHECKPOINTER;
     190        1026 :     AuxiliaryProcessMainCommon();
     191             : 
     192        1026 :     CheckpointerShmem->checkpointer_pid = MyProcPid;
     193             : 
     194             :     /*
     195             :      * Properly accept or ignore signals the postmaster might send us
     196             :      *
     197             :      * Note: we deliberately ignore SIGTERM, because during a standard Unix
     198             :      * system shutdown cycle, init will SIGTERM all processes at once.  We
     199             :      * want to wait for the backends to exit, whereupon the postmaster will
     200             :      * tell us it's okay to shut down (via SIGUSR2).
     201             :      */
     202        1026 :     pqsignal(SIGHUP, SignalHandlerForConfigReload);
     203        1026 :     pqsignal(SIGINT, ReqShutdownXLOG);
     204        1026 :     pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
     205             :     /* SIGQUIT handler was already set up by InitPostmasterChild */
     206        1026 :     pqsignal(SIGALRM, SIG_IGN);
     207        1026 :     pqsignal(SIGPIPE, SIG_IGN);
     208        1026 :     pqsignal(SIGUSR1, procsignal_sigusr1_handler);
     209        1026 :     pqsignal(SIGUSR2, SignalHandlerForShutdownRequest);
     210             : 
     211             :     /*
     212             :      * Reset some signals that are accepted by postmaster but not here
     213             :      */
     214        1026 :     pqsignal(SIGCHLD, SIG_DFL);
     215             : 
     216             :     /*
     217             :      * Initialize so that first time-driven event happens at the correct time.
     218             :      */
     219        1026 :     last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
     220             : 
     221             :     /*
     222             :      * Write out stats after shutdown. This needs to be called by exactly one
     223             :      * process during a normal shutdown, and since checkpointer is shut down
     224             :      * very late...
     225             :      *
     226             :      * While e.g. walsenders are active after the shutdown checkpoint has been
     227             :      * written (and thus could produce more stats), checkpointer stays around
     228             :      * after the shutdown checkpoint has been written. postmaster will only
     229             :      * signal checkpointer to exit after all processes that could emit stats
     230             :      * have been shut down.
     231             :      */
     232        1026 :     before_shmem_exit(pgstat_before_server_shutdown, 0);
     233             : 
     234             :     /*
     235             :      * Create a memory context that we will do all our work in.  We do this so
     236             :      * that we can reset the context during error recovery and thereby avoid
     237             :      * possible memory leaks.  Formerly this code just ran in
     238             :      * TopMemoryContext, but resetting that would be a really bad idea.
     239             :      */
     240        1026 :     checkpointer_context = AllocSetContextCreate(TopMemoryContext,
     241             :                                                  "Checkpointer",
     242             :                                                  ALLOCSET_DEFAULT_SIZES);
     243        1026 :     MemoryContextSwitchTo(checkpointer_context);
     244             : 
     245             :     /*
     246             :      * If an exception is encountered, processing resumes here.
     247             :      *
     248             :      * You might wonder why this isn't coded as an infinite loop around a
     249             :      * PG_TRY construct.  The reason is that this is the bottom of the
     250             :      * exception stack, and so with PG_TRY there would be no exception handler
     251             :      * in force at all during the CATCH part.  By leaving the outermost setjmp
     252             :      * always active, we have at least some chance of recovering from an error
     253             :      * during error recovery.  (If we get into an infinite loop thereby, it
     254             :      * will soon be stopped by overflow of elog.c's internal state stack.)
     255             :      *
     256             :      * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
     257             :      * (to wit, BlockSig) will be restored when longjmp'ing to here.  Thus,
     258             :      * signals other than SIGQUIT will be blocked until we complete error
     259             :      * recovery.  It might seem that this policy makes the HOLD_INTERRUPTS()
     260             :      * call redundant, but it is not since InterruptPending might be set
     261             :      * already.
     262             :      */
     263        1026 :     if (sigsetjmp(local_sigjmp_buf, 1) != 0)
     264             :     {
     265             :         /* Since not using PG_TRY, must reset error stack by hand */
     266           0 :         error_context_stack = NULL;
     267             : 
     268             :         /* Prevent interrupts while cleaning up */
     269           0 :         HOLD_INTERRUPTS();
     270             : 
     271             :         /* Report the error to the server log */
     272           0 :         EmitErrorReport();
     273             : 
     274             :         /*
     275             :          * These operations are really just a minimal subset of
     276             :          * AbortTransaction().  We don't have very many resources to worry
     277             :          * about in checkpointer, but we do have LWLocks, buffers, and temp
     278             :          * files.
     279             :          */
     280           0 :         LWLockReleaseAll();
     281           0 :         ConditionVariableCancelSleep();
     282           0 :         pgstat_report_wait_end();
     283           0 :         pgaio_error_cleanup();
     284           0 :         UnlockBuffers();
     285           0 :         ReleaseAuxProcessResources(false);
     286           0 :         AtEOXact_Buffers(false);
     287           0 :         AtEOXact_SMgr();
     288           0 :         AtEOXact_Files(false);
     289           0 :         AtEOXact_HashTables(false);
     290             : 
     291             :         /* Warn any waiting backends that the checkpoint failed. */
     292           0 :         if (ckpt_active)
     293             :         {
     294           0 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     295           0 :             CheckpointerShmem->ckpt_failed++;
     296           0 :             CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
     297           0 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     298             : 
     299           0 :             ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
     300             : 
     301           0 :             ckpt_active = false;
     302             :         }
     303             : 
     304             :         /*
     305             :          * Now return to normal top-level context and clear ErrorContext for
     306             :          * next time.
     307             :          */
     308           0 :         MemoryContextSwitchTo(checkpointer_context);
     309           0 :         FlushErrorState();
     310             : 
     311             :         /* Flush any leaked data in the top-level context */
     312           0 :         MemoryContextReset(checkpointer_context);
     313             : 
     314             :         /* Now we can allow interrupts again */
     315           0 :         RESUME_INTERRUPTS();
     316             : 
     317             :         /*
     318             :          * Sleep at least 1 second after any error.  A write error is likely
     319             :          * to be repeated, and we don't want to be filling the error logs as
     320             :          * fast as we can.
     321             :          */
     322           0 :         pg_usleep(1000000L);
     323             :     }
     324             : 
     325             :     /* We can now handle ereport(ERROR) */
     326        1026 :     PG_exception_stack = &local_sigjmp_buf;
     327             : 
     328             :     /*
     329             :      * Unblock signals (they were blocked when the postmaster forked us)
     330             :      */
     331        1026 :     sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
     332             : 
     333             :     /*
     334             :      * Ensure all shared memory values are set correctly for the config. Doing
     335             :      * this here ensures no race conditions from other concurrent updaters.
     336             :      */
     337        1026 :     UpdateSharedMemoryConfig();
     338             : 
     339             :     /*
     340             :      * Advertise our proc number that backends can use to wake us up while
     341             :      * we're sleeping.
     342             :      */
     343        1026 :     ProcGlobal->checkpointerProc = MyProcNumber;
     344             : 
     345             :     /*
     346             :      * Loop until we've been asked to write the shutdown checkpoint or
     347             :      * terminate.
     348             :      */
     349             :     for (;;)
     350        7156 :     {
     351        8182 :         bool        do_checkpoint = false;
     352        8182 :         int         flags = 0;
     353             :         pg_time_t   now;
     354             :         int         elapsed_secs;
     355             :         int         cur_timeout;
     356        8182 :         bool        chkpt_or_rstpt_requested = false;
     357        8182 :         bool        chkpt_or_rstpt_timed = false;
     358             : 
     359             :         /* Clear any already-pending wakeups */
     360        8182 :         ResetLatch(MyLatch);
     361             : 
     362             :         /*
     363             :          * Process any requests or signals received recently.
     364             :          */
     365        8182 :         AbsorbSyncRequests();
     366             : 
     367        8182 :         ProcessCheckpointerInterrupts();
     368        8182 :         if (ShutdownXLOGPending || ShutdownRequestPending)
     369             :             break;
     370             : 
     371             :         /*
     372             :          * Detect a pending checkpoint request by checking whether the flags
     373             :          * word in shared memory is nonzero.  We shouldn't need to acquire the
     374             :          * ckpt_lck for this.
     375             :          */
     376        7178 :         if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
     377             :         {
     378        2500 :             do_checkpoint = true;
     379        2500 :             chkpt_or_rstpt_requested = true;
     380             :         }
     381             : 
     382             :         /*
     383             :          * Force a checkpoint if too much time has elapsed since the last one.
     384             :          * Note that we count a timed checkpoint in stats only when this
     385             :          * occurs without an external request, but we set the CAUSE_TIME flag
     386             :          * bit even if there is also an external request.
     387             :          */
     388        7178 :         now = (pg_time_t) time(NULL);
     389        7178 :         elapsed_secs = now - last_checkpoint_time;
     390        7178 :         if (elapsed_secs >= CheckPointTimeout)
     391             :         {
     392           6 :             if (!do_checkpoint)
     393           6 :                 chkpt_or_rstpt_timed = true;
     394           6 :             do_checkpoint = true;
     395           6 :             flags |= CHECKPOINT_CAUSE_TIME;
     396             :         }
     397             : 
     398             :         /*
     399             :          * Do a checkpoint if requested.
     400             :          */
     401        7178 :         if (do_checkpoint)
     402             :         {
     403        2506 :             bool        ckpt_performed = false;
     404             :             bool        do_restartpoint;
     405             : 
     406             :             /* Check if we should perform a checkpoint or a restartpoint. */
     407        2506 :             do_restartpoint = RecoveryInProgress();
     408             : 
     409             :             /*
     410             :              * Atomically fetch the request flags to figure out what kind of a
     411             :              * checkpoint we should perform, and increase the started-counter
     412             :              * to acknowledge that we've started a new checkpoint.
     413             :              */
     414        2506 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     415        2506 :             flags |= CheckpointerShmem->ckpt_flags;
     416        2506 :             CheckpointerShmem->ckpt_flags = 0;
     417        2506 :             CheckpointerShmem->ckpt_started++;
     418        2506 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     419             : 
     420        2506 :             ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
     421             : 
     422             :             /*
     423             :              * The end-of-recovery checkpoint is a real checkpoint that's
     424             :              * performed while we're still in recovery.
     425             :              */
     426        2506 :             if (flags & CHECKPOINT_END_OF_RECOVERY)
     427          40 :                 do_restartpoint = false;
     428             : 
     429        2506 :             if (chkpt_or_rstpt_timed)
     430             :             {
     431           6 :                 chkpt_or_rstpt_timed = false;
     432           6 :                 if (do_restartpoint)
     433           0 :                     PendingCheckpointerStats.restartpoints_timed++;
     434             :                 else
     435           6 :                     PendingCheckpointerStats.num_timed++;
     436             :             }
     437             : 
     438        2506 :             if (chkpt_or_rstpt_requested)
     439             :             {
     440        2500 :                 chkpt_or_rstpt_requested = false;
     441        2500 :                 if (do_restartpoint)
     442        1052 :                     PendingCheckpointerStats.restartpoints_requested++;
     443             :                 else
     444        1448 :                     PendingCheckpointerStats.num_requested++;
     445             :             }
     446             : 
     447             :             /*
     448             :              * We will warn if (a) too soon since last checkpoint (whatever
     449             :              * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
     450             :              * since the last checkpoint start.  Note in particular that this
     451             :              * implementation will not generate warnings caused by
     452             :              * CheckPointTimeout < CheckPointWarning.
     453             :              */
     454        2506 :             if (!do_restartpoint &&
     455        1454 :                 (flags & CHECKPOINT_CAUSE_XLOG) &&
     456         378 :                 elapsed_secs < CheckPointWarning)
     457         378 :                 ereport(LOG,
     458             :                         (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
     459             :                                        "checkpoints are occurring too frequently (%d seconds apart)",
     460             :                                        elapsed_secs,
     461             :                                        elapsed_secs),
     462             :                          errhint("Consider increasing the configuration parameter \"%s\".", "max_wal_size")));
     463             : 
     464             :             /*
     465             :              * Initialize checkpointer-private variables used during
     466             :              * checkpoint.
     467             :              */
     468        2506 :             ckpt_active = true;
     469        2506 :             if (do_restartpoint)
     470        1052 :                 ckpt_start_recptr = GetXLogReplayRecPtr(NULL);
     471             :             else
     472        1454 :                 ckpt_start_recptr = GetInsertRecPtr();
     473        2506 :             ckpt_start_time = now;
     474        2506 :             ckpt_cached_elapsed = 0;
     475             : 
     476             :             /*
     477             :              * Do the checkpoint.
     478             :              */
     479        2506 :             if (!do_restartpoint)
     480        1454 :                 ckpt_performed = CreateCheckPoint(flags);
     481             :             else
     482        1052 :                 ckpt_performed = CreateRestartPoint(flags);
     483             : 
     484             :             /*
     485             :              * After any checkpoint, free all smgr objects.  Otherwise we
     486             :              * would never do so for dropped relations, as the checkpointer
     487             :              * does not process shared invalidation messages or call
     488             :              * AtEOXact_SMgr().
     489             :              */
     490        2506 :             smgrdestroyall();
     491             : 
     492             :             /*
     493             :              * Indicate checkpoint completion to any waiting backends.
     494             :              */
     495        2506 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     496        2506 :             CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
     497        2506 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     498             : 
     499        2506 :             ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
     500             : 
     501        2506 :             if (!do_restartpoint)
     502             :             {
     503             :                 /*
     504             :                  * Note we record the checkpoint start time not end time as
     505             :                  * last_checkpoint_time.  This is so that time-driven
     506             :                  * checkpoints happen at a predictable spacing.
     507             :                  */
     508        1454 :                 last_checkpoint_time = now;
     509             : 
     510        1454 :                 if (ckpt_performed)
     511        1454 :                     PendingCheckpointerStats.num_performed++;
     512             :             }
     513             :             else
     514             :             {
     515        1052 :                 if (ckpt_performed)
     516             :                 {
     517             :                     /*
     518             :                      * The same as for checkpoint. Please see the
     519             :                      * corresponding comment.
     520             :                      */
     521         334 :                     last_checkpoint_time = now;
     522             : 
     523         334 :                     PendingCheckpointerStats.restartpoints_performed++;
     524             :                 }
     525             :                 else
     526             :                 {
     527             :                     /*
     528             :                      * We were not able to perform the restartpoint
     529             :                      * (checkpoints throw an ERROR in case of error).  Most
     530             :                      * likely because we have not received any new checkpoint
     531             :                      * WAL records since the last restartpoint. Try again in
     532             :                      * 15 s.
     533             :                      */
     534         718 :                     last_checkpoint_time = now - CheckPointTimeout + 15;
     535             :                 }
     536             :             }
     537             : 
     538        2506 :             ckpt_active = false;
     539             : 
     540             :             /*
     541             :              * We may have received an interrupt during the checkpoint and the
     542             :              * latch might have been reset (e.g. in CheckpointWriteDelay).
     543             :              */
     544        2506 :             ProcessCheckpointerInterrupts();
     545        2506 :             if (ShutdownXLOGPending || ShutdownRequestPending)
     546             :                 break;
     547             :         }
     548             : 
     549             :         /* Check for archive_timeout and switch xlog files if necessary. */
     550        7164 :         CheckArchiveTimeout();
     551             : 
     552             :         /* Report pending statistics to the cumulative stats system */
     553        7164 :         pgstat_report_checkpointer();
     554        7164 :         pgstat_report_wal(true);
     555             : 
     556             :         /*
     557             :          * If any checkpoint flags have been set, redo the loop to handle the
     558             :          * checkpoint without sleeping.
     559             :          */
     560        7164 :         if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
     561         408 :             continue;
     562             : 
     563             :         /*
     564             :          * Sleep until we are signaled or it's time for another checkpoint or
     565             :          * xlog file switch.
     566             :          */
     567        6756 :         now = (pg_time_t) time(NULL);
     568        6756 :         elapsed_secs = now - last_checkpoint_time;
     569        6756 :         if (elapsed_secs >= CheckPointTimeout)
     570           0 :             continue;           /* no sleep for us ... */
     571        6756 :         cur_timeout = CheckPointTimeout - elapsed_secs;
     572        6756 :         if (XLogArchiveTimeout > 0 && !RecoveryInProgress())
     573             :         {
     574           0 :             elapsed_secs = now - last_xlog_switch_time;
     575           0 :             if (elapsed_secs >= XLogArchiveTimeout)
     576           0 :                 continue;       /* no sleep for us ... */
     577           0 :             cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
     578             :         }
     579             : 
     580        6756 :         (void) WaitLatch(MyLatch,
     581             :                          WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
     582             :                          cur_timeout * 1000L /* convert to ms */ ,
     583             :                          WAIT_EVENT_CHECKPOINTER_MAIN);
     584             :     }
     585             : 
     586             :     /*
     587             :      * From here on, elog(ERROR) should end with exit(1), not send control
     588             :      * back to the sigsetjmp block above.
     589             :      */
     590        1018 :     ExitOnAnyError = true;
     591             : 
     592        1018 :     if (ShutdownXLOGPending)
     593             :     {
     594             :         /*
     595             :          * Close down the database.
     596             :          *
     597             :          * Since ShutdownXLOG() creates restartpoint or checkpoint, and
     598             :          * updates the statistics, increment the checkpoint request and flush
     599             :          * out pending statistic.
     600             :          */
     601        1018 :         PendingCheckpointerStats.num_requested++;
     602        1018 :         ShutdownXLOG(0, 0);
     603        1018 :         pgstat_report_checkpointer();
     604        1018 :         pgstat_report_wal(true);
     605             : 
     606             :         /*
     607             :          * Tell postmaster that we're done.
     608             :          */
     609        1018 :         SendPostmasterSignal(PMSIGNAL_XLOG_IS_SHUTDOWN);
     610        1018 :         ShutdownXLOGPending = false;
     611             :     }
     612             : 
     613             :     /*
     614             :      * Wait until we're asked to shut down. By separating the writing of the
     615             :      * shutdown checkpoint from checkpointer exiting, checkpointer can perform
     616             :      * some should-be-as-late-as-possible work like writing out stats.
     617             :      */
     618             :     for (;;)
     619             :     {
     620             :         /* Clear any already-pending wakeups */
     621        2034 :         ResetLatch(MyLatch);
     622             : 
     623        2034 :         ProcessCheckpointerInterrupts();
     624             : 
     625        2034 :         if (ShutdownRequestPending)
     626        1018 :             break;
     627             : 
     628        1016 :         (void) WaitLatch(MyLatch,
     629             :                          WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
     630             :                          0,
     631             :                          WAIT_EVENT_CHECKPOINTER_SHUTDOWN);
     632             :     }
     633             : 
     634             :     /* Normal exit from the checkpointer is here */
     635        1018 :     proc_exit(0);               /* done */
     636             : }
     637             : 
     638             : /*
     639             :  * Process any new interrupts.
     640             :  */
     641             : static void
     642       12722 : ProcessCheckpointerInterrupts(void)
     643             : {
     644       12722 :     if (ProcSignalBarrierPending)
     645         118 :         ProcessProcSignalBarrier();
     646             : 
     647       12722 :     if (ConfigReloadPending)
     648             :     {
     649         118 :         ConfigReloadPending = false;
     650         118 :         ProcessConfigFile(PGC_SIGHUP);
     651             : 
     652             :         /*
     653             :          * Checkpointer is the last process to shut down, so we ask it to hold
     654             :          * the keys for a range of other tasks required most of which have
     655             :          * nothing to do with checkpointing at all.
     656             :          *
     657             :          * For various reasons, some config values can change dynamically so
     658             :          * the primary copy of them is held in shared memory to make sure all
     659             :          * backends see the same value.  We make Checkpointer responsible for
     660             :          * updating the shared memory copy if the parameter setting changes
     661             :          * because of SIGHUP.
     662             :          */
     663         118 :         UpdateSharedMemoryConfig();
     664             :     }
     665             : 
     666             :     /* Perform logging of memory contexts of this process */
     667       12722 :     if (LogMemoryContextPending)
     668           2 :         ProcessLogMemoryContextInterrupt();
     669       12722 : }
     670             : 
     671             : /*
     672             :  * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
     673             :  *
     674             :  * This will switch to a new WAL file and force an archive file write if
     675             :  * meaningful activity is recorded in the current WAL file. This includes most
     676             :  * writes, including just a single checkpoint record, but excludes WAL records
     677             :  * that were inserted with the XLOG_MARK_UNIMPORTANT flag being set (like
     678             :  * snapshots of running transactions).  Such records, depending on
     679             :  * configuration, occur on regular intervals and don't contain important
     680             :  * information.  This avoids generating archives with a few unimportant
     681             :  * records.
     682             :  */
     683             : static void
     684       26176 : CheckArchiveTimeout(void)
     685             : {
     686             :     pg_time_t   now;
     687             :     pg_time_t   last_time;
     688             :     XLogRecPtr  last_switch_lsn;
     689             : 
     690       26176 :     if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
     691       26176 :         return;
     692             : 
     693           0 :     now = (pg_time_t) time(NULL);
     694             : 
     695             :     /* First we do a quick check using possibly-stale local state. */
     696           0 :     if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
     697           0 :         return;
     698             : 
     699             :     /*
     700             :      * Update local state ... note that last_xlog_switch_time is the last time
     701             :      * a switch was performed *or requested*.
     702             :      */
     703           0 :     last_time = GetLastSegSwitchData(&last_switch_lsn);
     704             : 
     705           0 :     last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
     706             : 
     707             :     /* Now we can do the real checks */
     708           0 :     if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
     709             :     {
     710             :         /*
     711             :          * Switch segment only when "important" WAL has been logged since the
     712             :          * last segment switch (last_switch_lsn points to end of segment
     713             :          * switch occurred in).
     714             :          */
     715           0 :         if (GetLastImportantRecPtr() > last_switch_lsn)
     716             :         {
     717             :             XLogRecPtr  switchpoint;
     718             : 
     719             :             /* mark switch as unimportant, avoids triggering checkpoints */
     720           0 :             switchpoint = RequestXLogSwitch(true);
     721             : 
     722             :             /*
     723             :              * If the returned pointer points exactly to a segment boundary,
     724             :              * assume nothing happened.
     725             :              */
     726           0 :             if (XLogSegmentOffset(switchpoint, wal_segment_size) != 0)
     727           0 :                 elog(DEBUG1, "write-ahead log switch forced (\"archive_timeout\"=%d)",
     728             :                      XLogArchiveTimeout);
     729             :         }
     730             : 
     731             :         /*
     732             :          * Update state in any case, so we don't retry constantly when the
     733             :          * system is idle.
     734             :          */
     735           0 :         last_xlog_switch_time = now;
     736             :     }
     737             : }
     738             : 
     739             : /*
     740             :  * Returns true if a fast checkpoint request is pending.  (Note that this does
     741             :  * not check the *current* checkpoint's FAST flag, but whether there is one
     742             :  * pending behind it.)
     743             :  */
     744             : static bool
     745       94758 : FastCheckpointRequested(void)
     746             : {
     747       94758 :     volatile CheckpointerShmemStruct *cps = CheckpointerShmem;
     748             : 
     749             :     /*
     750             :      * We don't need to acquire the ckpt_lck in this case because we're only
     751             :      * looking at a single flag bit.
     752             :      */
     753       94758 :     if (cps->ckpt_flags & CHECKPOINT_FAST)
     754        7334 :         return true;
     755       87424 :     return false;
     756             : }
     757             : 
     758             : /*
     759             :  * CheckpointWriteDelay -- control rate of checkpoint
     760             :  *
     761             :  * This function is called after each page write performed by BufferSync().
     762             :  * It is responsible for throttling BufferSync()'s write rate to hit
     763             :  * checkpoint_completion_target.
     764             :  *
     765             :  * The checkpoint request flags should be passed in; currently the only one
     766             :  * examined is CHECKPOINT_FAST, which disables delays between writes.
     767             :  *
     768             :  * 'progress' is an estimate of how much of the work has been done, as a
     769             :  * fraction between 0.0 meaning none, and 1.0 meaning all done.
     770             :  */
     771             : void
     772      578088 : CheckpointWriteDelay(int flags, double progress)
     773             : {
     774             :     static int  absorb_counter = WRITES_PER_ABSORB;
     775             : 
     776             :     /* Do nothing if checkpoint is being executed by non-checkpointer process */
     777      578088 :     if (!AmCheckpointerProcess())
     778      103168 :         return;
     779             : 
     780             :     /*
     781             :      * Perform the usual duties and take a nap, unless we're behind schedule,
     782             :      * in which case we just try to catch up as quickly as possible.
     783             :      */
     784      474920 :     if (!(flags & CHECKPOINT_FAST) &&
     785       99968 :         !ShutdownXLOGPending &&
     786       94758 :         !ShutdownRequestPending &&
     787      182182 :         !FastCheckpointRequested() &&
     788       87424 :         IsCheckpointOnSchedule(progress))
     789             :     {
     790       19012 :         if (ConfigReloadPending)
     791             :         {
     792           0 :             ConfigReloadPending = false;
     793           0 :             ProcessConfigFile(PGC_SIGHUP);
     794             :             /* update shmem copies of config variables */
     795           0 :             UpdateSharedMemoryConfig();
     796             :         }
     797             : 
     798       19012 :         AbsorbSyncRequests();
     799       19012 :         absorb_counter = WRITES_PER_ABSORB;
     800             : 
     801       19012 :         CheckArchiveTimeout();
     802             : 
     803             :         /* Report interim statistics to the cumulative stats system */
     804       19012 :         pgstat_report_checkpointer();
     805             : 
     806             :         /*
     807             :          * This sleep used to be connected to bgwriter_delay, typically 200ms.
     808             :          * That resulted in more frequent wakeups if not much work to do.
     809             :          * Checkpointer and bgwriter are no longer related so take the Big
     810             :          * Sleep.
     811             :          */
     812       19012 :         WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH | WL_TIMEOUT,
     813             :                   100,
     814             :                   WAIT_EVENT_CHECKPOINT_WRITE_DELAY);
     815       19012 :         ResetLatch(MyLatch);
     816             :     }
     817      455908 :     else if (--absorb_counter <= 0)
     818             :     {
     819             :         /*
     820             :          * Absorb pending fsync requests after each WRITES_PER_ABSORB write
     821             :          * operations even when we don't sleep, to prevent overflow of the
     822             :          * fsync request queue.
     823             :          */
     824         188 :         AbsorbSyncRequests();
     825         188 :         absorb_counter = WRITES_PER_ABSORB;
     826             :     }
     827             : 
     828             :     /* Check for barrier events. */
     829      474920 :     if (ProcSignalBarrierPending)
     830          10 :         ProcessProcSignalBarrier();
     831             : }
     832             : 
     833             : /*
     834             :  * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
     835             :  *       (or restartpoint) in time?
     836             :  *
     837             :  * Compares the current progress against the time/segments elapsed since last
     838             :  * checkpoint, and returns true if the progress we've made this far is greater
     839             :  * than the elapsed time/segments.
     840             :  */
     841             : static bool
     842       87424 : IsCheckpointOnSchedule(double progress)
     843             : {
     844             :     XLogRecPtr  recptr;
     845             :     struct timeval now;
     846             :     double      elapsed_xlogs,
     847             :                 elapsed_time;
     848             : 
     849             :     Assert(ckpt_active);
     850             : 
     851             :     /* Scale progress according to checkpoint_completion_target. */
     852       87424 :     progress *= CheckPointCompletionTarget;
     853             : 
     854             :     /*
     855             :      * Check against the cached value first. Only do the more expensive
     856             :      * calculations once we reach the target previously calculated. Since
     857             :      * neither time or WAL insert pointer moves backwards, a freshly
     858             :      * calculated value can only be greater than or equal to the cached value.
     859             :      */
     860       87424 :     if (progress < ckpt_cached_elapsed)
     861       61008 :         return false;
     862             : 
     863             :     /*
     864             :      * Check progress against WAL segments written and CheckPointSegments.
     865             :      *
     866             :      * We compare the current WAL insert location against the location
     867             :      * computed before calling CreateCheckPoint. The code in XLogInsert that
     868             :      * actually triggers a checkpoint when CheckPointSegments is exceeded
     869             :      * compares against RedoRecPtr, so this is not completely accurate.
     870             :      * However, it's good enough for our purposes, we're only calculating an
     871             :      * estimate anyway.
     872             :      *
     873             :      * During recovery, we compare last replayed WAL record's location with
     874             :      * the location computed before calling CreateRestartPoint. That maintains
     875             :      * the same pacing as we have during checkpoints in normal operation, but
     876             :      * we might exceed max_wal_size by a fair amount. That's because there can
     877             :      * be a large gap between a checkpoint's redo-pointer and the checkpoint
     878             :      * record itself, and we only start the restartpoint after we've seen the
     879             :      * checkpoint record. (The gap is typically up to CheckPointSegments *
     880             :      * checkpoint_completion_target where checkpoint_completion_target is the
     881             :      * value that was in effect when the WAL was generated).
     882             :      */
     883       26416 :     if (RecoveryInProgress())
     884       11662 :         recptr = GetXLogReplayRecPtr(NULL);
     885             :     else
     886       14754 :         recptr = GetInsertRecPtr();
     887       26416 :     elapsed_xlogs = (((double) (recptr - ckpt_start_recptr)) /
     888       26416 :                      wal_segment_size) / CheckPointSegments;
     889             : 
     890       26416 :     if (progress < elapsed_xlogs)
     891             :     {
     892        7266 :         ckpt_cached_elapsed = elapsed_xlogs;
     893        7266 :         return false;
     894             :     }
     895             : 
     896             :     /*
     897             :      * Check progress against time elapsed and checkpoint_timeout.
     898             :      */
     899       19150 :     gettimeofday(&now, NULL);
     900       19150 :     elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
     901       19150 :                     now.tv_usec / 1000000.0) / CheckPointTimeout;
     902             : 
     903       19150 :     if (progress < elapsed_time)
     904             :     {
     905         138 :         ckpt_cached_elapsed = elapsed_time;
     906         138 :         return false;
     907             :     }
     908             : 
     909             :     /* It looks like we're on schedule. */
     910       19012 :     return true;
     911             : }
     912             : 
     913             : 
     914             : /* --------------------------------
     915             :  *      signal handler routines
     916             :  * --------------------------------
     917             :  */
     918             : 
     919             : /* SIGINT: set flag to trigger writing of shutdown checkpoint */
     920             : static void
     921        1020 : ReqShutdownXLOG(SIGNAL_ARGS)
     922             : {
     923        1020 :     ShutdownXLOGPending = true;
     924        1020 :     SetLatch(MyLatch);
     925        1020 : }
     926             : 
     927             : 
     928             : /* --------------------------------
     929             :  *      communication with backends
     930             :  * --------------------------------
     931             :  */
     932             : 
     933             : /*
     934             :  * CheckpointerShmemSize
     935             :  *      Compute space needed for checkpointer-related shared memory
     936             :  */
     937             : Size
     938        6114 : CheckpointerShmemSize(void)
     939             : {
     940             :     Size        size;
     941             : 
     942             :     /*
     943             :      * Currently, the size of the requests[] array is arbitrarily set equal to
     944             :      * NBuffers.  This may prove too large or small ...
     945             :      */
     946        6114 :     size = offsetof(CheckpointerShmemStruct, requests);
     947        6114 :     size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
     948             : 
     949        6114 :     return size;
     950             : }
     951             : 
     952             : /*
     953             :  * CheckpointerShmemInit
     954             :  *      Allocate and initialize checkpointer-related shared memory
     955             :  */
     956             : void
     957        2140 : CheckpointerShmemInit(void)
     958             : {
     959        2140 :     Size        size = CheckpointerShmemSize();
     960             :     bool        found;
     961             : 
     962        2140 :     CheckpointerShmem = (CheckpointerShmemStruct *)
     963        2140 :         ShmemInitStruct("Checkpointer Data",
     964             :                         size,
     965             :                         &found);
     966             : 
     967        2140 :     if (!found)
     968             :     {
     969             :         /*
     970             :          * First time through, so initialize.  Note that we zero the whole
     971             :          * requests array; this is so that CompactCheckpointerRequestQueue can
     972             :          * assume that any pad bytes in the request structs are zeroes.
     973             :          */
     974        2424 :         MemSet(CheckpointerShmem, 0, size);
     975        2140 :         SpinLockInit(&CheckpointerShmem->ckpt_lck);
     976        2140 :         CheckpointerShmem->max_requests = NBuffers;
     977        2140 :         ConditionVariableInit(&CheckpointerShmem->start_cv);
     978        2140 :         ConditionVariableInit(&CheckpointerShmem->done_cv);
     979             :     }
     980        2140 : }
     981             : 
     982             : /*
     983             :  * ExecCheckpoint
     984             :  *      Primary entry point for manual CHECKPOINT commands
     985             :  *
     986             :  * This is mainly a wrapper for RequestCheckpoint().
     987             :  */
     988             : void
     989         882 : ExecCheckpoint(ParseState *pstate, CheckPointStmt *stmt)
     990             : {
     991         882 :     bool        fast = true;
     992         882 :     bool        unlogged = false;
     993             : 
     994        1770 :     foreach_ptr(DefElem, opt, stmt->options)
     995             :     {
     996          30 :         if (strcmp(opt->defname, "mode") == 0)
     997             :         {
     998          12 :             char       *mode = defGetString(opt);
     999             : 
    1000          12 :             if (strcmp(mode, "spread") == 0)
    1001           0 :                 fast = false;
    1002          12 :             else if (strcmp(mode, "fast") != 0)
    1003           6 :                 ereport(ERROR,
    1004             :                         (errcode(ERRCODE_SYNTAX_ERROR),
    1005             :                          errmsg("unrecognized MODE option \"%s\"", mode),
    1006             :                          parser_errposition(pstate, opt->location)));
    1007             :         }
    1008          18 :         else if (strcmp(opt->defname, "flush_unlogged") == 0)
    1009          12 :             unlogged = defGetBoolean(opt);
    1010             :         else
    1011           6 :             ereport(ERROR,
    1012             :                     (errcode(ERRCODE_SYNTAX_ERROR),
    1013             :                      errmsg("unrecognized CHECKPOINT option \"%s\"", opt->defname),
    1014             :                      parser_errposition(pstate, opt->location)));
    1015             :     }
    1016             : 
    1017         870 :     if (!has_privs_of_role(GetUserId(), ROLE_PG_CHECKPOINT))
    1018           0 :         ereport(ERROR,
    1019             :                 (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
    1020             :         /* translator: %s is name of an SQL command (e.g., CHECKPOINT) */
    1021             :                  errmsg("permission denied to execute %s command",
    1022             :                         "CHECKPOINT"),
    1023             :                  errdetail("Only roles with privileges of the \"%s\" role may execute this command.",
    1024             :                            "pg_checkpoint")));
    1025             : 
    1026        1740 :     RequestCheckpoint(CHECKPOINT_WAIT |
    1027         870 :                       (fast ? CHECKPOINT_FAST : 0) |
    1028         870 :                       (unlogged ? CHECKPOINT_FLUSH_UNLOGGED : 0) |
    1029         870 :                       (RecoveryInProgress() ? 0 : CHECKPOINT_FORCE));
    1030         870 : }
    1031             : 
    1032             : /*
    1033             :  * RequestCheckpoint
    1034             :  *      Called in backend processes to request a checkpoint
    1035             :  *
    1036             :  * flags is a bitwise OR of the following:
    1037             :  *  CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
    1038             :  *  CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
    1039             :  *  CHECKPOINT_FAST: finish the checkpoint ASAP,
    1040             :  *      ignoring checkpoint_completion_target parameter.
    1041             :  *  CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
    1042             :  *      since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
    1043             :  *      CHECKPOINT_END_OF_RECOVERY, and the CHECKPOINT command).
    1044             :  *  CHECKPOINT_WAIT: wait for completion before returning (otherwise,
    1045             :  *      just signal checkpointer to do it, and return).
    1046             :  *  CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
    1047             :  *      (This affects logging, and in particular enables CheckPointWarning.)
    1048             :  */
    1049             : void
    1050        5322 : RequestCheckpoint(int flags)
    1051             : {
    1052             :     int         ntries;
    1053             :     int         old_failed,
    1054             :                 old_started;
    1055             : 
    1056             :     /*
    1057             :      * If in a standalone backend, just do it ourselves.
    1058             :      */
    1059        5322 :     if (!IsPostmasterEnvironment)
    1060             :     {
    1061             :         /*
    1062             :          * There's no point in doing slow checkpoints in a standalone backend,
    1063             :          * because there's no other backends the checkpoint could disrupt.
    1064             :          */
    1065         410 :         CreateCheckPoint(flags | CHECKPOINT_FAST);
    1066             : 
    1067             :         /* Free all smgr objects, as CheckpointerMain() normally would. */
    1068         410 :         smgrdestroyall();
    1069             : 
    1070         410 :         return;
    1071             :     }
    1072             : 
    1073             :     /*
    1074             :      * Atomically set the request flags, and take a snapshot of the counters.
    1075             :      * When we see ckpt_started > old_started, we know the flags we set here
    1076             :      * have been seen by checkpointer.
    1077             :      *
    1078             :      * Note that we OR the flags with any existing flags, to avoid overriding
    1079             :      * a "stronger" request by another backend.  The flag senses must be
    1080             :      * chosen to make this work!
    1081             :      */
    1082        4912 :     SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1083             : 
    1084        4912 :     old_failed = CheckpointerShmem->ckpt_failed;
    1085        4912 :     old_started = CheckpointerShmem->ckpt_started;
    1086        4912 :     CheckpointerShmem->ckpt_flags |= (flags | CHECKPOINT_REQUESTED);
    1087             : 
    1088        4912 :     SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1089             : 
    1090             :     /*
    1091             :      * Set checkpointer's latch to request checkpoint.  It's possible that the
    1092             :      * checkpointer hasn't started yet, so we will retry a few times if
    1093             :      * needed.  (Actually, more than a few times, since on slow or overloaded
    1094             :      * buildfarm machines, it's been observed that the checkpointer can take
    1095             :      * several seconds to start.)  However, if not told to wait for the
    1096             :      * checkpoint to occur, we consider failure to set the latch to be
    1097             :      * nonfatal and merely LOG it.  The checkpointer should see the request
    1098             :      * when it does start, with or without the SetLatch().
    1099             :      */
    1100             : #define MAX_SIGNAL_TRIES 600    /* max wait 60.0 sec */
    1101        4912 :     for (ntries = 0;; ntries++)
    1102          32 :     {
    1103        4944 :         volatile PROC_HDR *procglobal = ProcGlobal;
    1104        4944 :         ProcNumber  checkpointerProc = procglobal->checkpointerProc;
    1105             : 
    1106        4944 :         if (checkpointerProc == INVALID_PROC_NUMBER)
    1107             :         {
    1108          32 :             if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
    1109             :             {
    1110           0 :                 elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
    1111             :                      "could not notify checkpoint: checkpointer is not running");
    1112           0 :                 break;
    1113             :             }
    1114             :         }
    1115             :         else
    1116             :         {
    1117        4912 :             SetLatch(&GetPGProcByNumber(checkpointerProc)->procLatch);
    1118             :             /* notified successfully */
    1119        4912 :             break;
    1120             :         }
    1121             : 
    1122          32 :         CHECK_FOR_INTERRUPTS();
    1123          32 :         pg_usleep(100000L);     /* wait 0.1 sec, then retry */
    1124             :     }
    1125             : 
    1126             :     /*
    1127             :      * If requested, wait for completion.  We detect completion according to
    1128             :      * the algorithm given above.
    1129             :      */
    1130        4912 :     if (flags & CHECKPOINT_WAIT)
    1131             :     {
    1132             :         int         new_started,
    1133             :                     new_failed;
    1134             : 
    1135             :         /* Wait for a new checkpoint to start. */
    1136        1594 :         ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
    1137             :         for (;;)
    1138             :         {
    1139        2948 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1140        2948 :             new_started = CheckpointerShmem->ckpt_started;
    1141        2948 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1142             : 
    1143        2948 :             if (new_started != old_started)
    1144        1594 :                 break;
    1145             : 
    1146        1354 :             ConditionVariableSleep(&CheckpointerShmem->start_cv,
    1147             :                                    WAIT_EVENT_CHECKPOINT_START);
    1148             :         }
    1149        1594 :         ConditionVariableCancelSleep();
    1150             : 
    1151             :         /*
    1152             :          * We are waiting for ckpt_done >= new_started, in a modulo sense.
    1153             :          */
    1154        1594 :         ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
    1155             :         for (;;)
    1156        1380 :         {
    1157             :             int         new_done;
    1158             : 
    1159        2974 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1160        2974 :             new_done = CheckpointerShmem->ckpt_done;
    1161        2974 :             new_failed = CheckpointerShmem->ckpt_failed;
    1162        2974 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1163             : 
    1164        2974 :             if (new_done - new_started >= 0)
    1165        1594 :                 break;
    1166             : 
    1167        1380 :             ConditionVariableSleep(&CheckpointerShmem->done_cv,
    1168             :                                    WAIT_EVENT_CHECKPOINT_DONE);
    1169             :         }
    1170        1594 :         ConditionVariableCancelSleep();
    1171             : 
    1172        1594 :         if (new_failed != old_failed)
    1173           0 :             ereport(ERROR,
    1174             :                     (errmsg("checkpoint request failed"),
    1175             :                      errhint("Consult recent messages in the server log for details.")));
    1176             :     }
    1177             : }
    1178             : 
    1179             : /*
    1180             :  * ForwardSyncRequest
    1181             :  *      Forward a file-fsync request from a backend to the checkpointer
    1182             :  *
    1183             :  * Whenever a backend is compelled to write directly to a relation
    1184             :  * (which should be seldom, if the background writer is getting its job done),
    1185             :  * the backend calls this routine to pass over knowledge that the relation
    1186             :  * is dirty and must be fsync'd before next checkpoint.  We also use this
    1187             :  * opportunity to count such writes for statistical purposes.
    1188             :  *
    1189             :  * To avoid holding the lock for longer than necessary, we normally write
    1190             :  * to the requests[] queue without checking for duplicates.  The checkpointer
    1191             :  * will have to eliminate dups internally anyway.  However, if we discover
    1192             :  * that the queue is full, we make a pass over the entire queue to compact
    1193             :  * it.  This is somewhat expensive, but the alternative is for the backend
    1194             :  * to perform its own fsync, which is far more expensive in practice.  It
    1195             :  * is theoretically possible a backend fsync might still be necessary, if
    1196             :  * the queue is full and contains no duplicate entries.  In that case, we
    1197             :  * let the backend know by returning false.
    1198             :  */
    1199             : bool
    1200     2458956 : ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
    1201             : {
    1202             :     CheckpointerRequest *request;
    1203             :     bool        too_full;
    1204             : 
    1205     2458956 :     if (!IsUnderPostmaster)
    1206           0 :         return false;           /* probably shouldn't even get here */
    1207             : 
    1208     2458956 :     if (AmCheckpointerProcess())
    1209           0 :         elog(ERROR, "ForwardSyncRequest must not be called in checkpointer");
    1210             : 
    1211     2458956 :     LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
    1212             : 
    1213             :     /*
    1214             :      * If the checkpointer isn't running or the request queue is full, the
    1215             :      * backend will have to perform its own fsync request.  But before forcing
    1216             :      * that to happen, we can try to compact the request queue.
    1217             :      */
    1218     2458956 :     if (CheckpointerShmem->checkpointer_pid == 0 ||
    1219     2457616 :         (CheckpointerShmem->num_requests >= CheckpointerShmem->max_requests &&
    1220        4260 :          !CompactCheckpointerRequestQueue()))
    1221             :     {
    1222        4908 :         LWLockRelease(CheckpointerCommLock);
    1223        4908 :         return false;
    1224             :     }
    1225             : 
    1226             :     /* OK, insert request */
    1227     2454048 :     request = &CheckpointerShmem->requests[CheckpointerShmem->num_requests++];
    1228     2454048 :     request->ftag = *ftag;
    1229     2454048 :     request->type = type;
    1230             : 
    1231             :     /* If queue is more than half full, nudge the checkpointer to empty it */
    1232     2454048 :     too_full = (CheckpointerShmem->num_requests >=
    1233     2454048 :                 CheckpointerShmem->max_requests / 2);
    1234             : 
    1235     2454048 :     LWLockRelease(CheckpointerCommLock);
    1236             : 
    1237             :     /* ... but not till after we release the lock */
    1238     2454048 :     if (too_full)
    1239             :     {
    1240       62958 :         volatile PROC_HDR *procglobal = ProcGlobal;
    1241       62958 :         ProcNumber  checkpointerProc = procglobal->checkpointerProc;
    1242             : 
    1243       62958 :         if (checkpointerProc != INVALID_PROC_NUMBER)
    1244       62958 :             SetLatch(&GetPGProcByNumber(checkpointerProc)->procLatch);
    1245             :     }
    1246             : 
    1247     2454048 :     return true;
    1248             : }
    1249             : 
    1250             : /*
    1251             :  * CompactCheckpointerRequestQueue
    1252             :  *      Remove duplicates from the request queue to avoid backend fsyncs.
    1253             :  *      Returns "true" if any entries were removed.
    1254             :  *
    1255             :  * Although a full fsync request queue is not common, it can lead to severe
    1256             :  * performance problems when it does happen.  So far, this situation has
    1257             :  * only been observed to occur when the system is under heavy write load,
    1258             :  * and especially during the "sync" phase of a checkpoint.  Without this
    1259             :  * logic, each backend begins doing an fsync for every block written, which
    1260             :  * gets very expensive and can slow down the whole system.
    1261             :  *
    1262             :  * Trying to do this every time the queue is full could lose if there
    1263             :  * aren't any removable entries.  But that should be vanishingly rare in
    1264             :  * practice: there's one queue entry per shared buffer.
    1265             :  */
    1266             : static bool
    1267        4260 : CompactCheckpointerRequestQueue(void)
    1268             : {
    1269             :     struct CheckpointerSlotMapping
    1270             :     {
    1271             :         CheckpointerRequest request;
    1272             :         int         slot;
    1273             :     };
    1274             : 
    1275             :     int         n,
    1276             :                 preserve_count;
    1277        4260 :     int         num_skipped = 0;
    1278             :     HASHCTL     ctl;
    1279             :     HTAB       *htab;
    1280             :     bool       *skip_slot;
    1281             : 
    1282             :     /* must hold CheckpointerCommLock in exclusive mode */
    1283             :     Assert(LWLockHeldByMe(CheckpointerCommLock));
    1284             : 
    1285             :     /* Avoid memory allocations in a critical section. */
    1286        4260 :     if (CritSectionCount > 0)
    1287          14 :         return false;
    1288             : 
    1289             :     /* Initialize skip_slot array */
    1290        4246 :     skip_slot = palloc0(sizeof(bool) * CheckpointerShmem->num_requests);
    1291             : 
    1292             :     /* Initialize temporary hash table */
    1293        4246 :     ctl.keysize = sizeof(CheckpointerRequest);
    1294        4246 :     ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
    1295        4246 :     ctl.hcxt = CurrentMemoryContext;
    1296             : 
    1297        4246 :     htab = hash_create("CompactCheckpointerRequestQueue",
    1298        4246 :                        CheckpointerShmem->num_requests,
    1299             :                        &ctl,
    1300             :                        HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
    1301             : 
    1302             :     /*
    1303             :      * The basic idea here is that a request can be skipped if it's followed
    1304             :      * by a later, identical request.  It might seem more sensible to work
    1305             :      * backwards from the end of the queue and check whether a request is
    1306             :      * *preceded* by an earlier, identical request, in the hopes of doing less
    1307             :      * copying.  But that might change the semantics, if there's an
    1308             :      * intervening SYNC_FORGET_REQUEST or SYNC_FILTER_REQUEST, so we do it
    1309             :      * this way.  It would be possible to be even smarter if we made the code
    1310             :      * below understand the specific semantics of such requests (it could blow
    1311             :      * away preceding entries that would end up being canceled anyhow), but
    1312             :      * it's not clear that the extra complexity would buy us anything.
    1313             :      */
    1314      507638 :     for (n = 0; n < CheckpointerShmem->num_requests; n++)
    1315             :     {
    1316             :         CheckpointerRequest *request;
    1317             :         struct CheckpointerSlotMapping *slotmap;
    1318             :         bool        found;
    1319             : 
    1320             :         /*
    1321             :          * We use the request struct directly as a hashtable key.  This
    1322             :          * assumes that any padding bytes in the structs are consistently the
    1323             :          * same, which should be okay because we zeroed them in
    1324             :          * CheckpointerShmemInit.  Note also that RelFileLocator had better
    1325             :          * contain no pad bytes.
    1326             :          */
    1327      503392 :         request = &CheckpointerShmem->requests[n];
    1328      503392 :         slotmap = hash_search(htab, request, HASH_ENTER, &found);
    1329      503392 :         if (found)
    1330             :         {
    1331             :             /* Duplicate, so mark the previous occurrence as skippable */
    1332       28816 :             skip_slot[slotmap->slot] = true;
    1333       28816 :             num_skipped++;
    1334             :         }
    1335             :         /* Remember slot containing latest occurrence of this request value */
    1336      503392 :         slotmap->slot = n;
    1337             :     }
    1338             : 
    1339             :     /* Done with the hash table. */
    1340        4246 :     hash_destroy(htab);
    1341             : 
    1342             :     /* If no duplicates, we're out of luck. */
    1343        4246 :     if (!num_skipped)
    1344             :     {
    1345        3554 :         pfree(skip_slot);
    1346        3554 :         return false;
    1347             :     }
    1348             : 
    1349             :     /* We found some duplicates; remove them. */
    1350         692 :     preserve_count = 0;
    1351       81652 :     for (n = 0; n < CheckpointerShmem->num_requests; n++)
    1352             :     {
    1353       80960 :         if (skip_slot[n])
    1354       28816 :             continue;
    1355       52144 :         CheckpointerShmem->requests[preserve_count++] = CheckpointerShmem->requests[n];
    1356             :     }
    1357         692 :     ereport(DEBUG1,
    1358             :             (errmsg_internal("compacted fsync request queue from %d entries to %d entries",
    1359             :                              CheckpointerShmem->num_requests, preserve_count)));
    1360         692 :     CheckpointerShmem->num_requests = preserve_count;
    1361             : 
    1362             :     /* Cleanup. */
    1363         692 :     pfree(skip_slot);
    1364         692 :     return true;
    1365             : }
    1366             : 
    1367             : /*
    1368             :  * AbsorbSyncRequests
    1369             :  *      Retrieve queued sync requests and pass them to sync mechanism.
    1370             :  *
    1371             :  * This is exported because it must be called during CreateCheckPoint;
    1372             :  * we have to be sure we have accepted all pending requests just before
    1373             :  * we start fsync'ing.  Since CreateCheckPoint sometimes runs in
    1374             :  * non-checkpointer processes, do nothing if not checkpointer.
    1375             :  */
    1376             : void
    1377       40244 : AbsorbSyncRequests(void)
    1378             : {
    1379       40244 :     CheckpointerRequest *requests = NULL;
    1380             :     CheckpointerRequest *request;
    1381             :     int         n;
    1382             : 
    1383       40244 :     if (!AmCheckpointerProcess())
    1384        1264 :         return;
    1385             : 
    1386       38980 :     LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
    1387             : 
    1388             :     /*
    1389             :      * We try to avoid holding the lock for a long time by copying the request
    1390             :      * array, and processing the requests after releasing the lock.
    1391             :      *
    1392             :      * Once we have cleared the requests from shared memory, we have to PANIC
    1393             :      * if we then fail to absorb them (eg, because our hashtable runs out of
    1394             :      * memory).  This is because the system cannot run safely if we are unable
    1395             :      * to fsync what we have been told to fsync.  Fortunately, the hashtable
    1396             :      * is so small that the problem is quite unlikely to arise in practice.
    1397             :      */
    1398       38980 :     n = CheckpointerShmem->num_requests;
    1399       38980 :     if (n > 0)
    1400             :     {
    1401       19832 :         requests = (CheckpointerRequest *) palloc(n * sizeof(CheckpointerRequest));
    1402       19832 :         memcpy(requests, CheckpointerShmem->requests, n * sizeof(CheckpointerRequest));
    1403             :     }
    1404             : 
    1405       38980 :     START_CRIT_SECTION();
    1406             : 
    1407       38980 :     CheckpointerShmem->num_requests = 0;
    1408             : 
    1409       38980 :     LWLockRelease(CheckpointerCommLock);
    1410             : 
    1411     2267526 :     for (request = requests; n > 0; request++, n--)
    1412     2228546 :         RememberSyncRequest(&request->ftag, request->type);
    1413             : 
    1414       38980 :     END_CRIT_SECTION();
    1415             : 
    1416       38980 :     if (requests)
    1417       19832 :         pfree(requests);
    1418             : }
    1419             : 
    1420             : /*
    1421             :  * Update any shared memory configurations based on config parameters
    1422             :  */
    1423             : static void
    1424        1144 : UpdateSharedMemoryConfig(void)
    1425             : {
    1426             :     /* update global shmem state for sync rep */
    1427        1144 :     SyncRepUpdateSyncStandbysDefined();
    1428             : 
    1429             :     /*
    1430             :      * If full_page_writes has been changed by SIGHUP, we update it in shared
    1431             :      * memory and write an XLOG_FPW_CHANGE record.
    1432             :      */
    1433        1144 :     UpdateFullPageWrites();
    1434             : 
    1435        1144 :     elog(DEBUG2, "checkpointer updated shared memory configuration values");
    1436        1144 : }
    1437             : 
    1438             : /*
    1439             :  * FirstCallSinceLastCheckpoint allows a process to take an action once
    1440             :  * per checkpoint cycle by asynchronously checking for checkpoint completion.
    1441             :  */
    1442             : bool
    1443       25578 : FirstCallSinceLastCheckpoint(void)
    1444             : {
    1445             :     static int  ckpt_done = 0;
    1446             :     int         new_done;
    1447       25578 :     bool        FirstCall = false;
    1448             : 
    1449       25578 :     SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1450       25578 :     new_done = CheckpointerShmem->ckpt_done;
    1451       25578 :     SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1452             : 
    1453       25578 :     if (new_done != ckpt_done)
    1454        1168 :         FirstCall = true;
    1455             : 
    1456       25578 :     ckpt_done = new_done;
    1457             : 
    1458       25578 :     return FirstCall;
    1459             : }

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