LCOV - code coverage report
Current view: top level - src/backend/postmaster - checkpointer.c (source / functions) Hit Total Coverage
Test: PostgreSQL 13devel Lines: 245 343 71.4 %
Date: 2019-09-22 07:07:17 Functions: 16 18 88.9 %
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 checkpointer is started by the postmaster as soon as the startup
      14             :  * subprocess finishes, or as soon as recovery begins if we are doing archive
      15             :  * recovery.  It remains alive until the postmaster commands it to terminate.
      16             :  * Normal termination is by SIGUSR2, which instructs the checkpointer to
      17             :  * execute a shutdown checkpoint and then exit(0).  (All backends must be
      18             :  * stopped before SIGUSR2 is issued!)  Emergency termination is by SIGQUIT;
      19             :  * like any backend, the checkpointer 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) 1996-2019, PostgreSQL Global Development Group
      30             :  *
      31             :  *
      32             :  * IDENTIFICATION
      33             :  *    src/backend/postmaster/checkpointer.c
      34             :  *
      35             :  *-------------------------------------------------------------------------
      36             :  */
      37             : #include "postgres.h"
      38             : 
      39             : #include <signal.h>
      40             : #include <sys/time.h>
      41             : #include <time.h>
      42             : #include <unistd.h>
      43             : 
      44             : #include "access/xlog.h"
      45             : #include "access/xlog_internal.h"
      46             : #include "libpq/pqsignal.h"
      47             : #include "miscadmin.h"
      48             : #include "pgstat.h"
      49             : #include "postmaster/bgwriter.h"
      50             : #include "replication/syncrep.h"
      51             : #include "storage/bufmgr.h"
      52             : #include "storage/condition_variable.h"
      53             : #include "storage/fd.h"
      54             : #include "storage/ipc.h"
      55             : #include "storage/lwlock.h"
      56             : #include "storage/proc.h"
      57             : #include "storage/shmem.h"
      58             : #include "storage/smgr.h"
      59             : #include "storage/spin.h"
      60             : #include "utils/guc.h"
      61             : #include "utils/memutils.h"
      62             : #include "utils/resowner.h"
      63             : 
      64             : 
      65             : /*----------
      66             :  * Shared memory area for communication between checkpointer and backends
      67             :  *
      68             :  * The ckpt counters allow backends to watch for completion of a checkpoint
      69             :  * request they send.  Here's how it works:
      70             :  *  * At start of a checkpoint, checkpointer reads (and clears) the request
      71             :  *    flags and increments ckpt_started, while holding ckpt_lck.
      72             :  *  * On completion of a checkpoint, checkpointer sets ckpt_done to
      73             :  *    equal ckpt_started.
      74             :  *  * On failure of a checkpoint, checkpointer increments ckpt_failed
      75             :  *    and sets ckpt_done to equal ckpt_started.
      76             :  *
      77             :  * The algorithm for backends is:
      78             :  *  1. Record current values of ckpt_failed and ckpt_started, and
      79             :  *     set request flags, while holding ckpt_lck.
      80             :  *  2. Send signal to request checkpoint.
      81             :  *  3. Sleep until ckpt_started changes.  Now you know a checkpoint has
      82             :  *     begun since you started this algorithm (although *not* that it was
      83             :  *     specifically initiated by your signal), and that it is using your flags.
      84             :  *  4. Record new value of ckpt_started.
      85             :  *  5. Sleep until ckpt_done >= saved value of ckpt_started.  (Use modulo
      86             :  *     arithmetic here in case counters wrap around.)  Now you know a
      87             :  *     checkpoint has started and completed, but not whether it was
      88             :  *     successful.
      89             :  *  6. If ckpt_failed is different from the originally saved value,
      90             :  *     assume request failed; otherwise it was definitely successful.
      91             :  *
      92             :  * ckpt_flags holds the OR of the checkpoint request flags sent by all
      93             :  * requesting backends since the last checkpoint start.  The flags are
      94             :  * chosen so that OR'ing is the correct way to combine multiple requests.
      95             :  *
      96             :  * num_backend_writes is used to count the number of buffer writes performed
      97             :  * by user backend processes.  This counter should be wide enough that it
      98             :  * can't overflow during a single processing cycle.  num_backend_fsync
      99             :  * counts the subset of those writes that also had to do their own fsync,
     100             :  * because the checkpointer failed to absorb their request.
     101             :  *
     102             :  * The requests array holds fsync requests sent by backends and not yet
     103             :  * absorbed by the checkpointer.
     104             :  *
     105             :  * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
     106             :  * the requests fields are protected by CheckpointerCommLock.
     107             :  *----------
     108             :  */
     109             : typedef struct
     110             : {
     111             :     SyncRequestType type;       /* request type */
     112             :     FileTag     ftag;           /* file identifier */
     113             : } CheckpointerRequest;
     114             : 
     115             : typedef struct
     116             : {
     117             :     pid_t       checkpointer_pid;   /* PID (0 if not started) */
     118             : 
     119             :     slock_t     ckpt_lck;       /* protects all the ckpt_* fields */
     120             : 
     121             :     int         ckpt_started;   /* advances when checkpoint starts */
     122             :     int         ckpt_done;      /* advances when checkpoint done */
     123             :     int         ckpt_failed;    /* advances when checkpoint fails */
     124             : 
     125             :     int         ckpt_flags;     /* checkpoint flags, as defined in xlog.h */
     126             : 
     127             :     ConditionVariable start_cv; /* signaled when ckpt_started advances */
     128             :     ConditionVariable done_cv;  /* signaled when ckpt_done advances */
     129             : 
     130             :     uint32      num_backend_writes; /* counts user backend buffer writes */
     131             :     uint32      num_backend_fsync;  /* counts user backend fsync calls */
     132             : 
     133             :     int         num_requests;   /* current # of requests */
     134             :     int         max_requests;   /* allocated array size */
     135             :     CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
     136             : } CheckpointerShmemStruct;
     137             : 
     138             : static CheckpointerShmemStruct *CheckpointerShmem;
     139             : 
     140             : /* interval for calling AbsorbSyncRequests in CheckpointWriteDelay */
     141             : #define WRITES_PER_ABSORB       1000
     142             : 
     143             : /*
     144             :  * GUC parameters
     145             :  */
     146             : int         CheckPointTimeout = 300;
     147             : int         CheckPointWarning = 30;
     148             : double      CheckPointCompletionTarget = 0.5;
     149             : 
     150             : /*
     151             :  * Flags set by interrupt handlers for later service in the main loop.
     152             :  */
     153             : static volatile sig_atomic_t got_SIGHUP = false;
     154             : static volatile sig_atomic_t shutdown_requested = false;
     155             : 
     156             : /*
     157             :  * Private state
     158             :  */
     159             : static bool ckpt_active = false;
     160             : 
     161             : /* these values are valid when ckpt_active is true: */
     162             : static pg_time_t ckpt_start_time;
     163             : static XLogRecPtr ckpt_start_recptr;
     164             : static double ckpt_cached_elapsed;
     165             : 
     166             : static pg_time_t last_checkpoint_time;
     167             : static pg_time_t last_xlog_switch_time;
     168             : 
     169             : /* Prototypes for private functions */
     170             : 
     171             : static void CheckArchiveTimeout(void);
     172             : static bool IsCheckpointOnSchedule(double progress);
     173             : static bool ImmediateCheckpointRequested(void);
     174             : static bool CompactCheckpointerRequestQueue(void);
     175             : static void UpdateSharedMemoryConfig(void);
     176             : 
     177             : /* Signal handlers */
     178             : 
     179             : static void chkpt_quickdie(SIGNAL_ARGS);
     180             : static void ChkptSigHupHandler(SIGNAL_ARGS);
     181             : static void ReqCheckpointHandler(SIGNAL_ARGS);
     182             : static void chkpt_sigusr1_handler(SIGNAL_ARGS);
     183             : static void ReqShutdownHandler(SIGNAL_ARGS);
     184             : 
     185             : 
     186             : /*
     187             :  * Main entry point for checkpointer process
     188             :  *
     189             :  * This is invoked from AuxiliaryProcessMain, which has already created the
     190             :  * basic execution environment, but not enabled signals yet.
     191             :  */
     192             : void
     193         380 : CheckpointerMain(void)
     194             : {
     195             :     sigjmp_buf  local_sigjmp_buf;
     196             :     MemoryContext checkpointer_context;
     197             : 
     198         380 :     CheckpointerShmem->checkpointer_pid = MyProcPid;
     199             : 
     200             :     /*
     201             :      * Properly accept or ignore signals the postmaster might send us
     202             :      *
     203             :      * Note: we deliberately ignore SIGTERM, because during a standard Unix
     204             :      * system shutdown cycle, init will SIGTERM all processes at once.  We
     205             :      * want to wait for the backends to exit, whereupon the postmaster will
     206             :      * tell us it's okay to shut down (via SIGUSR2).
     207             :      */
     208         380 :     pqsignal(SIGHUP, ChkptSigHupHandler);   /* set flag to read config file */
     209         380 :     pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
     210         380 :     pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
     211         380 :     pqsignal(SIGQUIT, chkpt_quickdie);  /* hard crash time */
     212         380 :     pqsignal(SIGALRM, SIG_IGN);
     213         380 :     pqsignal(SIGPIPE, SIG_IGN);
     214         380 :     pqsignal(SIGUSR1, chkpt_sigusr1_handler);
     215         380 :     pqsignal(SIGUSR2, ReqShutdownHandler);  /* request shutdown */
     216             : 
     217             :     /*
     218             :      * Reset some signals that are accepted by postmaster but not here
     219             :      */
     220         380 :     pqsignal(SIGCHLD, SIG_DFL);
     221             : 
     222             :     /* We allow SIGQUIT (quickdie) at all times */
     223         380 :     sigdelset(&BlockSig, SIGQUIT);
     224             : 
     225             :     /*
     226             :      * Initialize so that first time-driven event happens at the correct time.
     227             :      */
     228         380 :     last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
     229             : 
     230             :     /*
     231             :      * Create a memory context that we will do all our work in.  We do this so
     232             :      * that we can reset the context during error recovery and thereby avoid
     233             :      * possible memory leaks.  Formerly this code just ran in
     234             :      * TopMemoryContext, but resetting that would be a really bad idea.
     235             :      */
     236         380 :     checkpointer_context = AllocSetContextCreate(TopMemoryContext,
     237             :                                                  "Checkpointer",
     238             :                                                  ALLOCSET_DEFAULT_SIZES);
     239         380 :     MemoryContextSwitchTo(checkpointer_context);
     240             : 
     241             :     /*
     242             :      * If an exception is encountered, processing resumes here.
     243             :      *
     244             :      * See notes in postgres.c about the design of this coding.
     245             :      */
     246         380 :     if (sigsetjmp(local_sigjmp_buf, 1) != 0)
     247             :     {
     248             :         /* Since not using PG_TRY, must reset error stack by hand */
     249           0 :         error_context_stack = NULL;
     250             : 
     251             :         /* Prevent interrupts while cleaning up */
     252           0 :         HOLD_INTERRUPTS();
     253             : 
     254             :         /* Report the error to the server log */
     255           0 :         EmitErrorReport();
     256             : 
     257             :         /*
     258             :          * These operations are really just a minimal subset of
     259             :          * AbortTransaction().  We don't have very many resources to worry
     260             :          * about in checkpointer, but we do have LWLocks, buffers, and temp
     261             :          * files.
     262             :          */
     263           0 :         LWLockReleaseAll();
     264           0 :         ConditionVariableCancelSleep();
     265           0 :         pgstat_report_wait_end();
     266           0 :         AbortBufferIO();
     267           0 :         UnlockBuffers();
     268           0 :         ReleaseAuxProcessResources(false);
     269           0 :         AtEOXact_Buffers(false);
     270           0 :         AtEOXact_SMgr();
     271           0 :         AtEOXact_Files(false);
     272           0 :         AtEOXact_HashTables(false);
     273             : 
     274             :         /* Warn any waiting backends that the checkpoint failed. */
     275           0 :         if (ckpt_active)
     276             :         {
     277           0 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     278           0 :             CheckpointerShmem->ckpt_failed++;
     279           0 :             CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
     280           0 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     281             : 
     282           0 :             ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
     283             : 
     284           0 :             ckpt_active = false;
     285             :         }
     286             : 
     287             :         /*
     288             :          * Now return to normal top-level context and clear ErrorContext for
     289             :          * next time.
     290             :          */
     291           0 :         MemoryContextSwitchTo(checkpointer_context);
     292           0 :         FlushErrorState();
     293             : 
     294             :         /* Flush any leaked data in the top-level context */
     295           0 :         MemoryContextResetAndDeleteChildren(checkpointer_context);
     296             : 
     297             :         /* Now we can allow interrupts again */
     298           0 :         RESUME_INTERRUPTS();
     299             : 
     300             :         /*
     301             :          * Sleep at least 1 second after any error.  A write error is likely
     302             :          * to be repeated, and we don't want to be filling the error logs as
     303             :          * fast as we can.
     304             :          */
     305           0 :         pg_usleep(1000000L);
     306             : 
     307             :         /*
     308             :          * Close all open files after any error.  This is helpful on Windows,
     309             :          * where holding deleted files open causes various strange errors.
     310             :          * It's not clear we need it elsewhere, but shouldn't hurt.
     311             :          */
     312           0 :         smgrcloseall();
     313             :     }
     314             : 
     315             :     /* We can now handle ereport(ERROR) */
     316         380 :     PG_exception_stack = &local_sigjmp_buf;
     317             : 
     318             :     /*
     319             :      * Unblock signals (they were blocked when the postmaster forked us)
     320             :      */
     321         380 :     PG_SETMASK(&UnBlockSig);
     322             : 
     323             :     /*
     324             :      * Ensure all shared memory values are set correctly for the config. Doing
     325             :      * this here ensures no race conditions from other concurrent updaters.
     326             :      */
     327         380 :     UpdateSharedMemoryConfig();
     328             : 
     329             :     /*
     330             :      * Advertise our latch that backends can use to wake us up while we're
     331             :      * sleeping.
     332             :      */
     333         380 :     ProcGlobal->checkpointerLatch = &MyProc->procLatch;
     334             : 
     335             :     /*
     336             :      * Loop forever
     337             :      */
     338             :     for (;;)
     339        1458 :     {
     340        1838 :         bool        do_checkpoint = false;
     341        1838 :         int         flags = 0;
     342             :         pg_time_t   now;
     343             :         int         elapsed_secs;
     344             :         int         cur_timeout;
     345             : 
     346             :         /* Clear any already-pending wakeups */
     347        1838 :         ResetLatch(MyLatch);
     348             : 
     349             :         /*
     350             :          * Process any requests or signals received recently.
     351             :          */
     352        1838 :         AbsorbSyncRequests();
     353             : 
     354        1838 :         if (got_SIGHUP)
     355             :         {
     356          10 :             got_SIGHUP = false;
     357          10 :             ProcessConfigFile(PGC_SIGHUP);
     358             : 
     359             :             /*
     360             :              * Checkpointer is the last process to shut down, so we ask it to
     361             :              * hold the keys for a range of other tasks required most of which
     362             :              * have nothing to do with checkpointing at all.
     363             :              *
     364             :              * For various reasons, some config values can change dynamically
     365             :              * so the primary copy of them is held in shared memory to make
     366             :              * sure all backends see the same value.  We make Checkpointer
     367             :              * responsible for updating the shared memory copy if the
     368             :              * parameter setting changes because of SIGHUP.
     369             :              */
     370          10 :             UpdateSharedMemoryConfig();
     371             :         }
     372        1838 :         if (shutdown_requested)
     373             :         {
     374             :             /*
     375             :              * From here on, elog(ERROR) should end with exit(1), not send
     376             :              * control back to the sigsetjmp block above
     377             :              */
     378         374 :             ExitOnAnyError = true;
     379             :             /* Close down the database */
     380         374 :             ShutdownXLOG(0, 0);
     381             :             /* Normal exit from the checkpointer is here */
     382         374 :             proc_exit(0);       /* done */
     383             :         }
     384             : 
     385             :         /*
     386             :          * Detect a pending checkpoint request by checking whether the flags
     387             :          * word in shared memory is nonzero.  We shouldn't need to acquire the
     388             :          * ckpt_lck for this.
     389             :          */
     390        1464 :         if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
     391             :         {
     392         536 :             do_checkpoint = true;
     393         536 :             BgWriterStats.m_requested_checkpoints++;
     394             :         }
     395             : 
     396             :         /*
     397             :          * Force a checkpoint if too much time has elapsed since the last one.
     398             :          * Note that we count a timed checkpoint in stats only when this
     399             :          * occurs without an external request, but we set the CAUSE_TIME flag
     400             :          * bit even if there is also an external request.
     401             :          */
     402        1464 :         now = (pg_time_t) time(NULL);
     403        1464 :         elapsed_secs = now - last_checkpoint_time;
     404        1464 :         if (elapsed_secs >= CheckPointTimeout)
     405             :         {
     406           0 :             if (!do_checkpoint)
     407           0 :                 BgWriterStats.m_timed_checkpoints++;
     408           0 :             do_checkpoint = true;
     409           0 :             flags |= CHECKPOINT_CAUSE_TIME;
     410             :         }
     411             : 
     412             :         /*
     413             :          * Do a checkpoint if requested.
     414             :          */
     415        1464 :         if (do_checkpoint)
     416             :         {
     417         536 :             bool        ckpt_performed = false;
     418             :             bool        do_restartpoint;
     419             : 
     420             :             /*
     421             :              * Check if we should perform a checkpoint or a restartpoint. As a
     422             :              * side-effect, RecoveryInProgress() initializes TimeLineID if
     423             :              * it's not set yet.
     424             :              */
     425         536 :             do_restartpoint = RecoveryInProgress();
     426             : 
     427             :             /*
     428             :              * Atomically fetch the request flags to figure out what kind of a
     429             :              * checkpoint we should perform, and increase the started-counter
     430             :              * to acknowledge that we've started a new checkpoint.
     431             :              */
     432         536 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     433         536 :             flags |= CheckpointerShmem->ckpt_flags;
     434         536 :             CheckpointerShmem->ckpt_flags = 0;
     435         536 :             CheckpointerShmem->ckpt_started++;
     436         536 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     437             : 
     438         536 :             ConditionVariableBroadcast(&CheckpointerShmem->start_cv);
     439             : 
     440             :             /*
     441             :              * The end-of-recovery checkpoint is a real checkpoint that's
     442             :              * performed while we're still in recovery.
     443             :              */
     444         536 :             if (flags & CHECKPOINT_END_OF_RECOVERY)
     445           0 :                 do_restartpoint = false;
     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        1060 :             if (!do_restartpoint &&
     455         534 :                 (flags & CHECKPOINT_CAUSE_XLOG) &&
     456          10 :                 elapsed_secs < CheckPointWarning)
     457           8 :                 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 \"max_wal_size\".")));
     463             : 
     464             :             /*
     465             :              * Initialize checkpointer-private variables used during
     466             :              * checkpoint.
     467             :              */
     468         536 :             ckpt_active = true;
     469         536 :             if (do_restartpoint)
     470          12 :                 ckpt_start_recptr = GetXLogReplayRecPtr(NULL);
     471             :             else
     472         524 :                 ckpt_start_recptr = GetInsertRecPtr();
     473         536 :             ckpt_start_time = now;
     474         536 :             ckpt_cached_elapsed = 0;
     475             : 
     476             :             /*
     477             :              * Do the checkpoint.
     478             :              */
     479         536 :             if (!do_restartpoint)
     480             :             {
     481         524 :                 CreateCheckPoint(flags);
     482         524 :                 ckpt_performed = true;
     483             :             }
     484             :             else
     485          12 :                 ckpt_performed = CreateRestartPoint(flags);
     486             : 
     487             :             /*
     488             :              * After any checkpoint, close all smgr files.  This is so we
     489             :              * won't hang onto smgr references to deleted files indefinitely.
     490             :              */
     491         536 :             smgrcloseall();
     492             : 
     493             :             /*
     494             :              * Indicate checkpoint completion to any waiting backends.
     495             :              */
     496         536 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     497         536 :             CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
     498         536 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     499             : 
     500         536 :             ConditionVariableBroadcast(&CheckpointerShmem->done_cv);
     501             : 
     502         536 :             if (ckpt_performed)
     503             :             {
     504             :                 /*
     505             :                  * Note we record the checkpoint start time not end time as
     506             :                  * last_checkpoint_time.  This is so that time-driven
     507             :                  * checkpoints happen at a predictable spacing.
     508             :                  */
     509         534 :                 last_checkpoint_time = now;
     510             :             }
     511             :             else
     512             :             {
     513             :                 /*
     514             :                  * We were not able to perform the restartpoint (checkpoints
     515             :                  * throw an ERROR in case of error).  Most likely because we
     516             :                  * have not received any new checkpoint WAL records since the
     517             :                  * last restartpoint. Try again in 15 s.
     518             :                  */
     519           2 :                 last_checkpoint_time = now - CheckPointTimeout + 15;
     520             :             }
     521             : 
     522         536 :             ckpt_active = false;
     523             :         }
     524             : 
     525             :         /* Check for archive_timeout and switch xlog files if necessary. */
     526        1464 :         CheckArchiveTimeout();
     527             : 
     528             :         /*
     529             :          * Send off activity statistics to the stats collector.  (The reason
     530             :          * why we re-use bgwriter-related code for this is that the bgwriter
     531             :          * and checkpointer used to be just one process.  It's probably not
     532             :          * worth the trouble to split the stats support into two independent
     533             :          * stats message types.)
     534             :          */
     535        1464 :         pgstat_send_bgwriter();
     536             : 
     537             :         /*
     538             :          * Sleep until we are signaled or it's time for another checkpoint or
     539             :          * xlog file switch.
     540             :          */
     541        1464 :         now = (pg_time_t) time(NULL);
     542        1464 :         elapsed_secs = now - last_checkpoint_time;
     543        1464 :         if (elapsed_secs >= CheckPointTimeout)
     544           0 :             continue;           /* no sleep for us ... */
     545        1464 :         cur_timeout = CheckPointTimeout - elapsed_secs;
     546        1464 :         if (XLogArchiveTimeout > 0 && !RecoveryInProgress())
     547             :         {
     548           0 :             elapsed_secs = now - last_xlog_switch_time;
     549           0 :             if (elapsed_secs >= XLogArchiveTimeout)
     550           0 :                 continue;       /* no sleep for us ... */
     551           0 :             cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
     552             :         }
     553             : 
     554        1464 :         (void) WaitLatch(MyLatch,
     555             :                          WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
     556             :                          cur_timeout * 1000L /* convert to ms */ ,
     557             :                          WAIT_EVENT_CHECKPOINTER_MAIN);
     558             :     }
     559             : }
     560             : 
     561             : /*
     562             :  * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
     563             :  *
     564             :  * This will switch to a new WAL file and force an archive file write if
     565             :  * meaningful activity is recorded in the current WAL file. This includes most
     566             :  * writes, including just a single checkpoint record, but excludes WAL records
     567             :  * that were inserted with the XLOG_MARK_UNIMPORTANT flag being set (like
     568             :  * snapshots of running transactions).  Such records, depending on
     569             :  * configuration, occur on regular intervals and don't contain important
     570             :  * information.  This avoids generating archives with a few unimportant
     571             :  * records.
     572             :  */
     573             : static void
     574        2742 : CheckArchiveTimeout(void)
     575             : {
     576             :     pg_time_t   now;
     577             :     pg_time_t   last_time;
     578             :     XLogRecPtr  last_switch_lsn;
     579             : 
     580        2742 :     if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
     581        5484 :         return;
     582             : 
     583           0 :     now = (pg_time_t) time(NULL);
     584             : 
     585             :     /* First we do a quick check using possibly-stale local state. */
     586           0 :     if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
     587           0 :         return;
     588             : 
     589             :     /*
     590             :      * Update local state ... note that last_xlog_switch_time is the last time
     591             :      * a switch was performed *or requested*.
     592             :      */
     593           0 :     last_time = GetLastSegSwitchData(&last_switch_lsn);
     594             : 
     595           0 :     last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
     596             : 
     597             :     /* Now we can do the real checks */
     598           0 :     if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
     599             :     {
     600             :         /*
     601             :          * Switch segment only when "important" WAL has been logged since the
     602             :          * last segment switch (last_switch_lsn points to end of segment
     603             :          * switch occurred in).
     604             :          */
     605           0 :         if (GetLastImportantRecPtr() > last_switch_lsn)
     606             :         {
     607             :             XLogRecPtr  switchpoint;
     608             : 
     609             :             /* mark switch as unimportant, avoids triggering checkpoints */
     610           0 :             switchpoint = RequestXLogSwitch(true);
     611             : 
     612             :             /*
     613             :              * If the returned pointer points exactly to a segment boundary,
     614             :              * assume nothing happened.
     615             :              */
     616           0 :             if (XLogSegmentOffset(switchpoint, wal_segment_size) != 0)
     617           0 :                 elog(DEBUG1, "write-ahead log switch forced (archive_timeout=%d)",
     618             :                      XLogArchiveTimeout);
     619             :         }
     620             : 
     621             :         /*
     622             :          * Update state in any case, so we don't retry constantly when the
     623             :          * system is idle.
     624             :          */
     625           0 :         last_xlog_switch_time = now;
     626             :     }
     627             : }
     628             : 
     629             : /*
     630             :  * Returns true if an immediate checkpoint request is pending.  (Note that
     631             :  * this does not check the *current* checkpoint's IMMEDIATE flag, but whether
     632             :  * there is one pending behind it.)
     633             :  */
     634             : static bool
     635       29790 : ImmediateCheckpointRequested(void)
     636             : {
     637       29790 :     volatile CheckpointerShmemStruct *cps = CheckpointerShmem;
     638             : 
     639             :     /*
     640             :      * We don't need to acquire the ckpt_lck in this case because we're only
     641             :      * looking at a single flag bit.
     642             :      */
     643       29790 :     if (cps->ckpt_flags & CHECKPOINT_IMMEDIATE)
     644         214 :         return true;
     645       29576 :     return false;
     646             : }
     647             : 
     648             : /*
     649             :  * CheckpointWriteDelay -- control rate of checkpoint
     650             :  *
     651             :  * This function is called after each page write performed by BufferSync().
     652             :  * It is responsible for throttling BufferSync()'s write rate to hit
     653             :  * checkpoint_completion_target.
     654             :  *
     655             :  * The checkpoint request flags should be passed in; currently the only one
     656             :  * examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
     657             :  *
     658             :  * 'progress' is an estimate of how much of the work has been done, as a
     659             :  * fraction between 0.0 meaning none, and 1.0 meaning all done.
     660             :  */
     661             : void
     662      463708 : CheckpointWriteDelay(int flags, double progress)
     663             : {
     664             :     static int  absorb_counter = WRITES_PER_ABSORB;
     665             : 
     666             :     /* Do nothing if checkpoint is being executed by non-checkpointer process */
     667      463708 :     if (!AmCheckpointerProcess())
     668      370948 :         return;
     669             : 
     670             :     /*
     671             :      * Perform the usual duties and take a nap, unless we're behind schedule,
     672             :      * in which case we just try to catch up as quickly as possible.
     673             :      */
     674      125796 :     if (!(flags & CHECKPOINT_IMMEDIATE) &&
     675       62826 :         !shutdown_requested &&
     676       59366 :         !ImmediateCheckpointRequested() &&
     677       29576 :         IsCheckpointOnSchedule(progress))
     678             :     {
     679        1278 :         if (got_SIGHUP)
     680             :         {
     681           0 :             got_SIGHUP = false;
     682           0 :             ProcessConfigFile(PGC_SIGHUP);
     683             :             /* update shmem copies of config variables */
     684           0 :             UpdateSharedMemoryConfig();
     685             :         }
     686             : 
     687        1278 :         AbsorbSyncRequests();
     688        1278 :         absorb_counter = WRITES_PER_ABSORB;
     689             : 
     690        1278 :         CheckArchiveTimeout();
     691             : 
     692             :         /*
     693             :          * Report interim activity statistics to the stats collector.
     694             :          */
     695        1278 :         pgstat_send_bgwriter();
     696             : 
     697             :         /*
     698             :          * This sleep used to be connected to bgwriter_delay, typically 200ms.
     699             :          * That resulted in more frequent wakeups if not much work to do.
     700             :          * Checkpointer and bgwriter are no longer related so take the Big
     701             :          * Sleep.
     702             :          */
     703        1278 :         pg_usleep(100000L);
     704             :     }
     705       91482 :     else if (--absorb_counter <= 0)
     706             :     {
     707             :         /*
     708             :          * Absorb pending fsync requests after each WRITES_PER_ABSORB write
     709             :          * operations even when we don't sleep, to prevent overflow of the
     710             :          * fsync request queue.
     711             :          */
     712          36 :         AbsorbSyncRequests();
     713          36 :         absorb_counter = WRITES_PER_ABSORB;
     714             :     }
     715             : }
     716             : 
     717             : /*
     718             :  * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
     719             :  *       (or restartpoint) in time?
     720             :  *
     721             :  * Compares the current progress against the time/segments elapsed since last
     722             :  * checkpoint, and returns true if the progress we've made this far is greater
     723             :  * than the elapsed time/segments.
     724             :  */
     725             : static bool
     726       29576 : IsCheckpointOnSchedule(double progress)
     727             : {
     728             :     XLogRecPtr  recptr;
     729             :     struct timeval now;
     730             :     double      elapsed_xlogs,
     731             :                 elapsed_time;
     732             : 
     733             :     Assert(ckpt_active);
     734             : 
     735             :     /* Scale progress according to checkpoint_completion_target. */
     736       29576 :     progress *= CheckPointCompletionTarget;
     737             : 
     738             :     /*
     739             :      * Check against the cached value first. Only do the more expensive
     740             :      * calculations once we reach the target previously calculated. Since
     741             :      * neither time or WAL insert pointer moves backwards, a freshly
     742             :      * calculated value can only be greater than or equal to the cached value.
     743             :      */
     744       29576 :     if (progress < ckpt_cached_elapsed)
     745       27880 :         return false;
     746             : 
     747             :     /*
     748             :      * Check progress against WAL segments written and CheckPointSegments.
     749             :      *
     750             :      * We compare the current WAL insert location against the location
     751             :      * computed before calling CreateCheckPoint. The code in XLogInsert that
     752             :      * actually triggers a checkpoint when CheckPointSegments is exceeded
     753             :      * compares against RedoRecPtr, so this is not completely accurate.
     754             :      * However, it's good enough for our purposes, we're only calculating an
     755             :      * estimate anyway.
     756             :      *
     757             :      * During recovery, we compare last replayed WAL record's location with
     758             :      * the location computed before calling CreateRestartPoint. That maintains
     759             :      * the same pacing as we have during checkpoints in normal operation, but
     760             :      * we might exceed max_wal_size by a fair amount. That's because there can
     761             :      * be a large gap between a checkpoint's redo-pointer and the checkpoint
     762             :      * record itself, and we only start the restartpoint after we've seen the
     763             :      * checkpoint record. (The gap is typically up to CheckPointSegments *
     764             :      * checkpoint_completion_target where checkpoint_completion_target is the
     765             :      * value that was in effect when the WAL was generated).
     766             :      */
     767        1696 :     if (RecoveryInProgress())
     768           0 :         recptr = GetXLogReplayRecPtr(NULL);
     769             :     else
     770        1696 :         recptr = GetInsertRecPtr();
     771        3392 :     elapsed_xlogs = (((double) (recptr - ckpt_start_recptr)) /
     772        1696 :                      wal_segment_size) / CheckPointSegments;
     773             : 
     774        1696 :     if (progress < elapsed_xlogs)
     775             :     {
     776         412 :         ckpt_cached_elapsed = elapsed_xlogs;
     777         412 :         return false;
     778             :     }
     779             : 
     780             :     /*
     781             :      * Check progress against time elapsed and checkpoint_timeout.
     782             :      */
     783        1284 :     gettimeofday(&now, NULL);
     784        3852 :     elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
     785        2568 :                     now.tv_usec / 1000000.0) / CheckPointTimeout;
     786             : 
     787        1284 :     if (progress < elapsed_time)
     788             :     {
     789           6 :         ckpt_cached_elapsed = elapsed_time;
     790           6 :         return false;
     791             :     }
     792             : 
     793             :     /* It looks like we're on schedule. */
     794        1278 :     return true;
     795             : }
     796             : 
     797             : 
     798             : /* --------------------------------
     799             :  *      signal handler routines
     800             :  * --------------------------------
     801             :  */
     802             : 
     803             : /*
     804             :  * chkpt_quickdie() occurs when signalled SIGQUIT by the postmaster.
     805             :  *
     806             :  * Some backend has bought the farm,
     807             :  * so we need to stop what we're doing and exit.
     808             :  */
     809             : static void
     810           0 : chkpt_quickdie(SIGNAL_ARGS)
     811             : {
     812             :     /*
     813             :      * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here
     814             :      * because shared memory may be corrupted, so we don't want to try to
     815             :      * clean up our transaction.  Just nail the windows shut and get out of
     816             :      * town.  The callbacks wouldn't be safe to run from a signal handler,
     817             :      * anyway.
     818             :      *
     819             :      * Note we do _exit(2) not _exit(0).  This is to force the postmaster into
     820             :      * a system reset cycle if someone sends a manual SIGQUIT to a random
     821             :      * backend.  This is necessary precisely because we don't clean up our
     822             :      * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
     823             :      * should ensure the postmaster sees this as a crash, too, but no harm in
     824             :      * being doubly sure.)
     825             :      */
     826           0 :     _exit(2);
     827             : }
     828             : 
     829             : /* SIGHUP: set flag to re-read config file at next convenient time */
     830             : static void
     831          10 : ChkptSigHupHandler(SIGNAL_ARGS)
     832             : {
     833          10 :     int         save_errno = errno;
     834             : 
     835          10 :     got_SIGHUP = true;
     836          10 :     SetLatch(MyLatch);
     837             : 
     838          10 :     errno = save_errno;
     839          10 : }
     840             : 
     841             : /* SIGINT: set flag to run a normal checkpoint right away */
     842             : static void
     843         536 : ReqCheckpointHandler(SIGNAL_ARGS)
     844             : {
     845         536 :     int         save_errno = errno;
     846             : 
     847             :     /*
     848             :      * The signalling process should have set ckpt_flags nonzero, so all we
     849             :      * need do is ensure that our main loop gets kicked out of any wait.
     850             :      */
     851         536 :     SetLatch(MyLatch);
     852             : 
     853         536 :     errno = save_errno;
     854         536 : }
     855             : 
     856             : /* SIGUSR1: used for latch wakeups */
     857             : static void
     858         538 : chkpt_sigusr1_handler(SIGNAL_ARGS)
     859             : {
     860         538 :     int         save_errno = errno;
     861             : 
     862         538 :     latch_sigusr1_handler();
     863             : 
     864         538 :     errno = save_errno;
     865         538 : }
     866             : 
     867             : /* SIGUSR2: set flag to run a shutdown checkpoint and exit */
     868             : static void
     869         374 : ReqShutdownHandler(SIGNAL_ARGS)
     870             : {
     871         374 :     int         save_errno = errno;
     872             : 
     873         374 :     shutdown_requested = true;
     874         374 :     SetLatch(MyLatch);
     875             : 
     876         374 :     errno = save_errno;
     877         374 : }
     878             : 
     879             : 
     880             : /* --------------------------------
     881             :  *      communication with backends
     882             :  * --------------------------------
     883             :  */
     884             : 
     885             : /*
     886             :  * CheckpointerShmemSize
     887             :  *      Compute space needed for checkpointer-related shared memory
     888             :  */
     889             : Size
     890        3716 : CheckpointerShmemSize(void)
     891             : {
     892             :     Size        size;
     893             : 
     894             :     /*
     895             :      * Currently, the size of the requests[] array is arbitrarily set equal to
     896             :      * NBuffers.  This may prove too large or small ...
     897             :      */
     898        3716 :     size = offsetof(CheckpointerShmemStruct, requests);
     899        3716 :     size = add_size(size, mul_size(NBuffers, sizeof(CheckpointerRequest)));
     900             : 
     901        3716 :     return size;
     902             : }
     903             : 
     904             : /*
     905             :  * CheckpointerShmemInit
     906             :  *      Allocate and initialize checkpointer-related shared memory
     907             :  */
     908             : void
     909        1856 : CheckpointerShmemInit(void)
     910             : {
     911        1856 :     Size        size = CheckpointerShmemSize();
     912             :     bool        found;
     913             : 
     914        1856 :     CheckpointerShmem = (CheckpointerShmemStruct *)
     915        1856 :         ShmemInitStruct("Checkpointer Data",
     916             :                         size,
     917             :                         &found);
     918             : 
     919        1856 :     if (!found)
     920             :     {
     921             :         /*
     922             :          * First time through, so initialize.  Note that we zero the whole
     923             :          * requests array; this is so that CompactCheckpointerRequestQueue can
     924             :          * assume that any pad bytes in the request structs are zeroes.
     925             :          */
     926        1856 :         MemSet(CheckpointerShmem, 0, size);
     927        1856 :         SpinLockInit(&CheckpointerShmem->ckpt_lck);
     928        1856 :         CheckpointerShmem->max_requests = NBuffers;
     929        1856 :         ConditionVariableInit(&CheckpointerShmem->start_cv);
     930        1856 :         ConditionVariableInit(&CheckpointerShmem->done_cv);
     931             :     }
     932        1856 : }
     933             : 
     934             : /*
     935             :  * RequestCheckpoint
     936             :  *      Called in backend processes to request a checkpoint
     937             :  *
     938             :  * flags is a bitwise OR of the following:
     939             :  *  CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
     940             :  *  CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
     941             :  *  CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
     942             :  *      ignoring checkpoint_completion_target parameter.
     943             :  *  CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
     944             :  *      since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
     945             :  *      CHECKPOINT_END_OF_RECOVERY).
     946             :  *  CHECKPOINT_WAIT: wait for completion before returning (otherwise,
     947             :  *      just signal checkpointer to do it, and return).
     948             :  *  CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
     949             :  *      (This affects logging, and in particular enables CheckPointWarning.)
     950             :  */
     951             : void
     952        2008 : RequestCheckpoint(int flags)
     953             : {
     954             :     int         ntries;
     955             :     int         old_failed,
     956             :                 old_started;
     957             : 
     958             :     /*
     959             :      * If in a standalone backend, just do it ourselves.
     960             :      */
     961        2008 :     if (!IsPostmasterEnvironment)
     962             :     {
     963             :         /*
     964             :          * There's no point in doing slow checkpoints in a standalone backend,
     965             :          * because there's no other backends the checkpoint could disrupt.
     966             :          */
     967        1280 :         CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);
     968             : 
     969             :         /*
     970             :          * After any checkpoint, close all smgr files.  This is so we won't
     971             :          * hang onto smgr references to deleted files indefinitely.
     972             :          */
     973        1280 :         smgrcloseall();
     974             : 
     975        1280 :         return;
     976             :     }
     977             : 
     978             :     /*
     979             :      * Atomically set the request flags, and take a snapshot of the counters.
     980             :      * When we see ckpt_started > old_started, we know the flags we set here
     981             :      * have been seen by checkpointer.
     982             :      *
     983             :      * Note that we OR the flags with any existing flags, to avoid overriding
     984             :      * a "stronger" request by another backend.  The flag senses must be
     985             :      * chosen to make this work!
     986             :      */
     987         728 :     SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
     988             : 
     989         728 :     old_failed = CheckpointerShmem->ckpt_failed;
     990         728 :     old_started = CheckpointerShmem->ckpt_started;
     991         728 :     CheckpointerShmem->ckpt_flags |= (flags | CHECKPOINT_REQUESTED);
     992             : 
     993         728 :     SpinLockRelease(&CheckpointerShmem->ckpt_lck);
     994             : 
     995             :     /*
     996             :      * Send signal to request checkpoint.  It's possible that the checkpointer
     997             :      * hasn't started yet, or is in process of restarting, so we will retry a
     998             :      * few times if needed.  (Actually, more than a few times, since on slow
     999             :      * or overloaded buildfarm machines, it's been observed that the
    1000             :      * checkpointer can take several seconds to start.)  However, if not told
    1001             :      * to wait for the checkpoint to occur, we consider failure to send the
    1002             :      * signal to be nonfatal and merely LOG it.  The checkpointer should see
    1003             :      * the request when it does start, with or without getting a signal.
    1004             :      */
    1005             : #define MAX_SIGNAL_TRIES 600    /* max wait 60.0 sec */
    1006         728 :     for (ntries = 0;; ntries++)
    1007             :     {
    1008         728 :         if (CheckpointerShmem->checkpointer_pid == 0)
    1009             :         {
    1010           0 :             if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
    1011             :             {
    1012           0 :                 elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
    1013             :                      "could not signal for checkpoint: checkpointer is not running");
    1014           0 :                 break;
    1015             :             }
    1016             :         }
    1017         728 :         else if (kill(CheckpointerShmem->checkpointer_pid, SIGINT) != 0)
    1018             :         {
    1019           0 :             if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
    1020             :             {
    1021           0 :                 elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
    1022             :                      "could not signal for checkpoint: %m");
    1023           0 :                 break;
    1024             :             }
    1025             :         }
    1026             :         else
    1027         728 :             break;              /* signal sent successfully */
    1028             : 
    1029           0 :         CHECK_FOR_INTERRUPTS();
    1030           0 :         pg_usleep(100000L);     /* wait 0.1 sec, then retry */
    1031             :     }
    1032             : 
    1033             :     /*
    1034             :      * If requested, wait for completion.  We detect completion according to
    1035             :      * the algorithm given above.
    1036             :      */
    1037         728 :     if (flags & CHECKPOINT_WAIT)
    1038             :     {
    1039             :         int         new_started,
    1040             :                     new_failed;
    1041             : 
    1042             :         /* Wait for a new checkpoint to start. */
    1043         676 :         ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
    1044             :         for (;;)
    1045             :         {
    1046        1480 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1047        1078 :             new_started = CheckpointerShmem->ckpt_started;
    1048        1078 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1049             : 
    1050        1078 :             if (new_started != old_started)
    1051         676 :                 break;
    1052             : 
    1053         402 :             ConditionVariableSleep(&CheckpointerShmem->start_cv,
    1054             :                                    WAIT_EVENT_CHECKPOINT_START);
    1055             :         }
    1056         676 :         ConditionVariableCancelSleep();
    1057             : 
    1058             :         /*
    1059             :          * We are waiting for ckpt_done >= new_started, in a modulo sense.
    1060             :          */
    1061         676 :         ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
    1062             :         for (;;)
    1063         344 :         {
    1064             :             int         new_done;
    1065             : 
    1066        1020 :             SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1067        1020 :             new_done = CheckpointerShmem->ckpt_done;
    1068        1020 :             new_failed = CheckpointerShmem->ckpt_failed;
    1069        1020 :             SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1070             : 
    1071        1020 :             if (new_done - new_started >= 0)
    1072         676 :                 break;
    1073             : 
    1074         344 :             ConditionVariableSleep(&CheckpointerShmem->done_cv,
    1075             :                                    WAIT_EVENT_CHECKPOINT_DONE);
    1076             :         }
    1077         676 :         ConditionVariableCancelSleep();
    1078             : 
    1079         676 :         if (new_failed != old_failed)
    1080           0 :             ereport(ERROR,
    1081             :                     (errmsg("checkpoint request failed"),
    1082             :                      errhint("Consult recent messages in the server log for details.")));
    1083             :     }
    1084             : }
    1085             : 
    1086             : /*
    1087             :  * ForwardSyncRequest
    1088             :  *      Forward a file-fsync request from a backend to the checkpointer
    1089             :  *
    1090             :  * Whenever a backend is compelled to write directly to a relation
    1091             :  * (which should be seldom, if the background writer is getting its job done),
    1092             :  * the backend calls this routine to pass over knowledge that the relation
    1093             :  * is dirty and must be fsync'd before next checkpoint.  We also use this
    1094             :  * opportunity to count such writes for statistical purposes.
    1095             :  *
    1096             :  * To avoid holding the lock for longer than necessary, we normally write
    1097             :  * to the requests[] queue without checking for duplicates.  The checkpointer
    1098             :  * will have to eliminate dups internally anyway.  However, if we discover
    1099             :  * that the queue is full, we make a pass over the entire queue to compact
    1100             :  * it.  This is somewhat expensive, but the alternative is for the backend
    1101             :  * to perform its own fsync, which is far more expensive in practice.  It
    1102             :  * is theoretically possible a backend fsync might still be necessary, if
    1103             :  * the queue is full and contains no duplicate entries.  In that case, we
    1104             :  * let the backend know by returning false.
    1105             :  */
    1106             : bool
    1107      355354 : ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
    1108             : {
    1109             :     CheckpointerRequest *request;
    1110             :     bool        too_full;
    1111             : 
    1112      355354 :     if (!IsUnderPostmaster)
    1113           0 :         return false;           /* probably shouldn't even get here */
    1114             : 
    1115      355354 :     if (AmCheckpointerProcess())
    1116           0 :         elog(ERROR, "ForwardSyncRequest must not be called in checkpointer");
    1117             : 
    1118      355354 :     LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
    1119             : 
    1120             :     /* Count all backend writes regardless of if they fit in the queue */
    1121      355354 :     if (!AmBackgroundWriterProcess())
    1122      353906 :         CheckpointerShmem->num_backend_writes++;
    1123             : 
    1124             :     /*
    1125             :      * If the checkpointer isn't running or the request queue is full, the
    1126             :      * backend will have to perform its own fsync request.  But before forcing
    1127             :      * that to happen, we can try to compact the request queue.
    1128             :      */
    1129      710708 :     if (CheckpointerShmem->checkpointer_pid == 0 ||
    1130      355354 :         (CheckpointerShmem->num_requests >= CheckpointerShmem->max_requests &&
    1131           0 :          !CompactCheckpointerRequestQueue()))
    1132             :     {
    1133             :         /*
    1134             :          * Count the subset of writes where backends have to do their own
    1135             :          * fsync
    1136             :          */
    1137           0 :         if (!AmBackgroundWriterProcess())
    1138           0 :             CheckpointerShmem->num_backend_fsync++;
    1139           0 :         LWLockRelease(CheckpointerCommLock);
    1140           0 :         return false;
    1141             :     }
    1142             : 
    1143             :     /* OK, insert request */
    1144      355354 :     request = &CheckpointerShmem->requests[CheckpointerShmem->num_requests++];
    1145      355354 :     request->ftag = *ftag;
    1146      355354 :     request->type = type;
    1147             : 
    1148             :     /* If queue is more than half full, nudge the checkpointer to empty it */
    1149      710708 :     too_full = (CheckpointerShmem->num_requests >=
    1150      355354 :                 CheckpointerShmem->max_requests / 2);
    1151             : 
    1152      355354 :     LWLockRelease(CheckpointerCommLock);
    1153             : 
    1154             :     /* ... but not till after we release the lock */
    1155      355354 :     if (too_full && ProcGlobal->checkpointerLatch)
    1156        1292 :         SetLatch(ProcGlobal->checkpointerLatch);
    1157             : 
    1158      355354 :     return true;
    1159             : }
    1160             : 
    1161             : /*
    1162             :  * CompactCheckpointerRequestQueue
    1163             :  *      Remove duplicates from the request queue to avoid backend fsyncs.
    1164             :  *      Returns "true" if any entries were removed.
    1165             :  *
    1166             :  * Although a full fsync request queue is not common, it can lead to severe
    1167             :  * performance problems when it does happen.  So far, this situation has
    1168             :  * only been observed to occur when the system is under heavy write load,
    1169             :  * and especially during the "sync" phase of a checkpoint.  Without this
    1170             :  * logic, each backend begins doing an fsync for every block written, which
    1171             :  * gets very expensive and can slow down the whole system.
    1172             :  *
    1173             :  * Trying to do this every time the queue is full could lose if there
    1174             :  * aren't any removable entries.  But that should be vanishingly rare in
    1175             :  * practice: there's one queue entry per shared buffer.
    1176             :  */
    1177             : static bool
    1178           0 : CompactCheckpointerRequestQueue(void)
    1179             : {
    1180             :     struct CheckpointerSlotMapping
    1181             :     {
    1182             :         CheckpointerRequest request;
    1183             :         int         slot;
    1184             :     };
    1185             : 
    1186             :     int         n,
    1187             :                 preserve_count;
    1188           0 :     int         num_skipped = 0;
    1189             :     HASHCTL     ctl;
    1190             :     HTAB       *htab;
    1191             :     bool       *skip_slot;
    1192             : 
    1193             :     /* must hold CheckpointerCommLock in exclusive mode */
    1194             :     Assert(LWLockHeldByMe(CheckpointerCommLock));
    1195             : 
    1196             :     /* Initialize skip_slot array */
    1197           0 :     skip_slot = palloc0(sizeof(bool) * CheckpointerShmem->num_requests);
    1198             : 
    1199             :     /* Initialize temporary hash table */
    1200           0 :     MemSet(&ctl, 0, sizeof(ctl));
    1201           0 :     ctl.keysize = sizeof(CheckpointerRequest);
    1202           0 :     ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
    1203           0 :     ctl.hcxt = CurrentMemoryContext;
    1204             : 
    1205           0 :     htab = hash_create("CompactCheckpointerRequestQueue",
    1206           0 :                        CheckpointerShmem->num_requests,
    1207             :                        &ctl,
    1208             :                        HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
    1209             : 
    1210             :     /*
    1211             :      * The basic idea here is that a request can be skipped if it's followed
    1212             :      * by a later, identical request.  It might seem more sensible to work
    1213             :      * backwards from the end of the queue and check whether a request is
    1214             :      * *preceded* by an earlier, identical request, in the hopes of doing less
    1215             :      * copying.  But that might change the semantics, if there's an
    1216             :      * intervening SYNC_FORGET_REQUEST or SYNC_FILTER_REQUEST, so we do it
    1217             :      * this way.  It would be possible to be even smarter if we made the code
    1218             :      * below understand the specific semantics of such requests (it could blow
    1219             :      * away preceding entries that would end up being canceled anyhow), but
    1220             :      * it's not clear that the extra complexity would buy us anything.
    1221             :      */
    1222           0 :     for (n = 0; n < CheckpointerShmem->num_requests; n++)
    1223             :     {
    1224             :         CheckpointerRequest *request;
    1225             :         struct CheckpointerSlotMapping *slotmap;
    1226             :         bool        found;
    1227             : 
    1228             :         /*
    1229             :          * We use the request struct directly as a hashtable key.  This
    1230             :          * assumes that any padding bytes in the structs are consistently the
    1231             :          * same, which should be okay because we zeroed them in
    1232             :          * CheckpointerShmemInit.  Note also that RelFileNode had better
    1233             :          * contain no pad bytes.
    1234             :          */
    1235           0 :         request = &CheckpointerShmem->requests[n];
    1236           0 :         slotmap = hash_search(htab, request, HASH_ENTER, &found);
    1237           0 :         if (found)
    1238             :         {
    1239             :             /* Duplicate, so mark the previous occurrence as skippable */
    1240           0 :             skip_slot[slotmap->slot] = true;
    1241           0 :             num_skipped++;
    1242             :         }
    1243             :         /* Remember slot containing latest occurrence of this request value */
    1244           0 :         slotmap->slot = n;
    1245             :     }
    1246             : 
    1247             :     /* Done with the hash table. */
    1248           0 :     hash_destroy(htab);
    1249             : 
    1250             :     /* If no duplicates, we're out of luck. */
    1251           0 :     if (!num_skipped)
    1252             :     {
    1253           0 :         pfree(skip_slot);
    1254           0 :         return false;
    1255             :     }
    1256             : 
    1257             :     /* We found some duplicates; remove them. */
    1258           0 :     preserve_count = 0;
    1259           0 :     for (n = 0; n < CheckpointerShmem->num_requests; n++)
    1260             :     {
    1261           0 :         if (skip_slot[n])
    1262           0 :             continue;
    1263           0 :         CheckpointerShmem->requests[preserve_count++] = CheckpointerShmem->requests[n];
    1264             :     }
    1265           0 :     ereport(DEBUG1,
    1266             :             (errmsg("compacted fsync request queue from %d entries to %d entries",
    1267             :                     CheckpointerShmem->num_requests, preserve_count)));
    1268           0 :     CheckpointerShmem->num_requests = preserve_count;
    1269             : 
    1270             :     /* Cleanup. */
    1271           0 :     pfree(skip_slot);
    1272           0 :     return true;
    1273             : }
    1274             : 
    1275             : /*
    1276             :  * AbsorbSyncRequests
    1277             :  *      Retrieve queued sync requests and pass them to sync mechanism.
    1278             :  *
    1279             :  * This is exported because it must be called during CreateCheckPoint;
    1280             :  * we have to be sure we have accepted all pending requests just before
    1281             :  * we start fsync'ing.  Since CreateCheckPoint sometimes runs in
    1282             :  * non-checkpointer processes, do nothing if not checkpointer.
    1283             :  */
    1284             : void
    1285        9142 : AbsorbSyncRequests(void)
    1286             : {
    1287        9142 :     CheckpointerRequest *requests = NULL;
    1288             :     CheckpointerRequest *request;
    1289             :     int         n;
    1290             : 
    1291        9142 :     if (!AmCheckpointerProcess())
    1292        2016 :         return;
    1293             : 
    1294        7126 :     LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
    1295             : 
    1296             :     /* Transfer stats counts into pending pgstats message */
    1297        7126 :     BgWriterStats.m_buf_written_backend += CheckpointerShmem->num_backend_writes;
    1298        7126 :     BgWriterStats.m_buf_fsync_backend += CheckpointerShmem->num_backend_fsync;
    1299             : 
    1300        7126 :     CheckpointerShmem->num_backend_writes = 0;
    1301        7126 :     CheckpointerShmem->num_backend_fsync = 0;
    1302             : 
    1303             :     /*
    1304             :      * We try to avoid holding the lock for a long time by copying the request
    1305             :      * array, and processing the requests after releasing the lock.
    1306             :      *
    1307             :      * Once we have cleared the requests from shared memory, we have to PANIC
    1308             :      * if we then fail to absorb them (eg, because our hashtable runs out of
    1309             :      * memory).  This is because the system cannot run safely if we are unable
    1310             :      * to fsync what we have been told to fsync.  Fortunately, the hashtable
    1311             :      * is so small that the problem is quite unlikely to arise in practice.
    1312             :      */
    1313        7126 :     n = CheckpointerShmem->num_requests;
    1314        7126 :     if (n > 0)
    1315             :     {
    1316        1264 :         requests = (CheckpointerRequest *) palloc(n * sizeof(CheckpointerRequest));
    1317        1264 :         memcpy(requests, CheckpointerShmem->requests, n * sizeof(CheckpointerRequest));
    1318             :     }
    1319             : 
    1320        7126 :     START_CRIT_SECTION();
    1321             : 
    1322        7126 :     CheckpointerShmem->num_requests = 0;
    1323             : 
    1324        7126 :     LWLockRelease(CheckpointerCommLock);
    1325             : 
    1326      328078 :     for (request = requests; n > 0; request++, n--)
    1327      320952 :         RememberSyncRequest(&request->ftag, request->type);
    1328             : 
    1329        7126 :     END_CRIT_SECTION();
    1330             : 
    1331        7126 :     if (requests)
    1332        1264 :         pfree(requests);
    1333             : }
    1334             : 
    1335             : /*
    1336             :  * Update any shared memory configurations based on config parameters
    1337             :  */
    1338             : static void
    1339         390 : UpdateSharedMemoryConfig(void)
    1340             : {
    1341             :     /* update global shmem state for sync rep */
    1342         390 :     SyncRepUpdateSyncStandbysDefined();
    1343             : 
    1344             :     /*
    1345             :      * If full_page_writes has been changed by SIGHUP, we update it in shared
    1346             :      * memory and write an XLOG_FPW_CHANGE record.
    1347             :      */
    1348         390 :     UpdateFullPageWrites();
    1349             : 
    1350         390 :     elog(DEBUG2, "checkpointer updated shared memory configuration values");
    1351         390 : }
    1352             : 
    1353             : /*
    1354             :  * FirstCallSinceLastCheckpoint allows a process to take an action once
    1355             :  * per checkpoint cycle by asynchronously checking for checkpoint completion.
    1356             :  */
    1357             : bool
    1358        9078 : FirstCallSinceLastCheckpoint(void)
    1359             : {
    1360             :     static int  ckpt_done = 0;
    1361             :     int         new_done;
    1362        9078 :     bool        FirstCall = false;
    1363             : 
    1364        9078 :     SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
    1365        9078 :     new_done = CheckpointerShmem->ckpt_done;
    1366        9078 :     SpinLockRelease(&CheckpointerShmem->ckpt_lck);
    1367             : 
    1368        9078 :     if (new_done != ckpt_done)
    1369         328 :         FirstCall = true;
    1370             : 
    1371        9078 :     ckpt_done = new_done;
    1372             : 
    1373        9078 :     return FirstCall;
    1374             : }

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