/src/postgres/src/backend/postmaster/checkpointer.c

Source
/*-------------------------------------------------------------------------
 *
 * checkpointer.c
 *
 * The checkpointer is new as of Postgres 9.2.  It handles all checkpoints.
 * Checkpoints are automatically dispatched after a certain amount of time has
 * elapsed since the last one, and it can be signaled to perform requested
 * checkpoints as well.  (The GUC parameter that mandates a checkpoint every
 * so many WAL segments is implemented by having backends signal when they
 * fill WAL segments; the checkpointer itself doesn't watch for the
 * condition.)
 *
 * The normal termination sequence is that checkpointer is instructed to
 * execute the shutdown checkpoint by SIGINT.  After that checkpointer waits
 * to be terminated via SIGUSR2, which instructs the checkpointer to exit(0).
 * All backends must be stopped before SIGINT or SIGUSR2 is issued!
 *
 * Emergency termination is by SIGQUIT; like any backend, the checkpointer
 * will simply abort and exit on SIGQUIT.
 *
 * If the checkpointer exits unexpectedly, the postmaster treats that the same
 * as a backend crash: shared memory may be corrupted, so remaining backends
 * should be killed by SIGQUIT and then a recovery cycle started.  (Even if
 * shared memory isn't corrupted, we have lost information about which
 * files need to be fsync'd for the next checkpoint, and so a system
 * restart needs to be forced.)
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *    src/backend/postmaster/checkpointer.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <sys/time.h>
#include <time.h>

#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogrecovery.h"
#include "catalog/pg_authid.h"
#include "commands/defrem.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/auxprocess.h"
#include "postmaster/bgwriter.h"
#include "postmaster/interrupt.h"
#include "replication/syncrep.h"
#include "storage/aio_subsys.h"
#include "storage/bufmgr.h"
#include "storage/condition_variable.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "storage/shmem.h"
#include "storage/smgr.h"
#include "storage/spin.h"
#include "utils/acl.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/resowner.h"


/*----------
 * Shared memory area for communication between checkpointer and backends
 *
 * The ckpt counters allow backends to watch for completion of a checkpoint
 * request they send.  Here's how it works:
 *  * At start of a checkpoint, checkpointer reads (and clears) the request
 *    flags and increments ckpt_started, while holding ckpt_lck.
 *  * On completion of a checkpoint, checkpointer sets ckpt_done to
 *    equal ckpt_started.
 *  * On failure of a checkpoint, checkpointer increments ckpt_failed
 *    and sets ckpt_done to equal ckpt_started.
 *
 * The algorithm for backends is:
 *  1. Record current values of ckpt_failed and ckpt_started, and
 *     set request flags, while holding ckpt_lck.
 *  2. Send signal to request checkpoint.
 *  3. Sleep until ckpt_started changes.  Now you know a checkpoint has
 *     begun since you started this algorithm (although *not* that it was
 *     specifically initiated by your signal), and that it is using your flags.
 *  4. Record new value of ckpt_started.
 *  5. Sleep until ckpt_done >= saved value of ckpt_started.  (Use modulo
 *     arithmetic here in case counters wrap around.)  Now you know a
 *     checkpoint has started and completed, but not whether it was
 *     successful.
 *  6. If ckpt_failed is different from the originally saved value,
 *     assume request failed; otherwise it was definitely successful.
 *
 * ckpt_flags holds the OR of the checkpoint request flags sent by all
 * requesting backends since the last checkpoint start.  The flags are
 * chosen so that OR'ing is the correct way to combine multiple requests.
 *
 * The requests array holds fsync requests sent by backends and not yet
 * absorbed by the checkpointer.
 *
 * Unlike the checkpoint fields, requests related fields are protected by
 * CheckpointerCommLock.
 *----------
 */
typedef struct
{
  SyncRequestType type;   /* request type */
  FileTag   ftag;     /* file identifier */
} CheckpointerRequest;

typedef struct
{
  pid_t   checkpointer_pid; /* PID (0 if not started) */

  slock_t   ckpt_lck;   /* protects all the ckpt_* fields */

  int     ckpt_started; /* advances when checkpoint starts */
  int     ckpt_done;    /* advances when checkpoint done */
  int     ckpt_failed;  /* advances when checkpoint fails */

  int     ckpt_flags;   /* checkpoint flags, as defined in xlog.h */

  ConditionVariable start_cv; /* signaled when ckpt_started advances */
  ConditionVariable done_cv;  /* signaled when ckpt_done advances */

  int     num_requests; /* current # of requests */
  int     max_requests; /* allocated array size */

  int     head;     /* Index of the first request in the ring
                 * buffer */
  int     tail;     /* Index of the last request in the ring
                 * buffer */

  /* The ring buffer of pending checkpointer requests */
  CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
} CheckpointerShmemStruct;

static CheckpointerShmemStruct *CheckpointerShmem;

/* interval for calling AbsorbSyncRequests in CheckpointWriteDelay */
#define WRITES_PER_ABSORB   1000

/* Maximum number of checkpointer requests to process in one batch */
#define CKPT_REQ_BATCH_SIZE 10000

/* Max number of requests the checkpointer request queue can hold */
#define MAX_CHECKPOINT_REQUESTS 10000000

/*
 * GUC parameters
 */
int     CheckPointTimeout = 300;
int     CheckPointWarning = 30;
double    CheckPointCompletionTarget = 0.9;

/*
 * Private state
 */
static bool ckpt_active = false;
static volatile sig_atomic_t ShutdownXLOGPending = false;

/* these values are valid when ckpt_active is true: */
static pg_time_t ckpt_start_time;
static XLogRecPtr ckpt_start_recptr;
static double ckpt_cached_elapsed;

static pg_time_t last_checkpoint_time;
static pg_time_t last_xlog_switch_time;

/* Prototypes for private functions */

static void ProcessCheckpointerInterrupts(void);
static void CheckArchiveTimeout(void);
static bool IsCheckpointOnSchedule(double progress);
static bool FastCheckpointRequested(void);
static bool CompactCheckpointerRequestQueue(void);
static void UpdateSharedMemoryConfig(void);

/* Signal handlers */
static void ReqShutdownXLOG(SIGNAL_ARGS);


/*
 * Main entry point for checkpointer process
 *
 * This is invoked from AuxiliaryProcessMain, which has already created the
 * basic execution environment, but not enabled signals yet.
 */
void
CheckpointerMain(const void *startup_data, size_t startup_data_len)
{
  sigjmp_buf  local_sigjmp_buf;
  MemoryContext checkpointer_context;

  Assert(startup_data_len == 0);

  MyBackendType = B_CHECKPOINTER;
  AuxiliaryProcessMainCommon();

  CheckpointerShmem->checkpointer_pid = MyProcPid;

  /*
   * Properly accept or ignore signals the postmaster might send us
   *
   * Note: we deliberately ignore SIGTERM, because during a standard Unix
   * system shutdown cycle, init will SIGTERM all processes at once.  We
   * want to wait for the backends to exit, whereupon the postmaster will
   * tell us it's okay to shut down (via SIGUSR2).
   */
  pqsignal(SIGHUP, SignalHandlerForConfigReload);
  pqsignal(SIGINT, ReqShutdownXLOG);
  pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
  /* SIGQUIT handler was already set up by InitPostmasterChild */
  pqsignal(SIGALRM, SIG_IGN);
  pqsignal(SIGPIPE, SIG_IGN);
  pqsignal(SIGUSR1, procsignal_sigusr1_handler);
  pqsignal(SIGUSR2, SignalHandlerForShutdownRequest);

  /*
   * Reset some signals that are accepted by postmaster but not here
   */
  pqsignal(SIGCHLD, SIG_DFL);

  /*
   * Initialize so that first time-driven event happens at the correct time.
   */
  last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);

  /*
   * Write out stats after shutdown. This needs to be called by exactly one
   * process during a normal shutdown, and since checkpointer is shut down
   * very late...
   *
   * While e.g. walsenders are active after the shutdown checkpoint has been
   * written (and thus could produce more stats), checkpointer stays around
   * after the shutdown checkpoint has been written. postmaster will only
   * signal checkpointer to exit after all processes that could emit stats
   * have been shut down.
   */
  before_shmem_exit(pgstat_before_server_shutdown, 0);

  /*
   * Create a memory context that we will do all our work in.  We do this so
   * that we can reset the context during error recovery and thereby avoid
   * possible memory leaks.  Formerly this code just ran in
   * TopMemoryContext, but resetting that would be a really bad idea.
   */
  checkpointer_context = AllocSetContextCreate(TopMemoryContext,
                         "Checkpointer",
                         ALLOCSET_DEFAULT_SIZES);
  MemoryContextSwitchTo(checkpointer_context);

  /*
   * If an exception is encountered, processing resumes here.
   *
   * You might wonder why this isn't coded as an infinite loop around a
   * PG_TRY construct.  The reason is that this is the bottom of the
   * exception stack, and so with PG_TRY there would be no exception handler
   * in force at all during the CATCH part.  By leaving the outermost setjmp
   * always active, we have at least some chance of recovering from an error
   * during error recovery.  (If we get into an infinite loop thereby, it
   * will soon be stopped by overflow of elog.c's internal state stack.)
   *
   * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
   * (to wit, BlockSig) will be restored when longjmp'ing to here.  Thus,
   * signals other than SIGQUIT will be blocked until we complete error
   * recovery.  It might seem that this policy makes the HOLD_INTERRUPTS()
   * call redundant, but it is not since InterruptPending might be set
   * already.
   */
  if (sigsetjmp(local_sigjmp_buf, 1) != 0)
  {
    /* Since not using PG_TRY, must reset error stack by hand */
    error_context_stack = NULL;

    /* Prevent interrupts while cleaning up */
    HOLD_INTERRUPTS();

    /* Report the error to the server log */
    EmitErrorReport();

    /*
     * These operations are really just a minimal subset of
     * AbortTransaction().  We don't have very many resources to worry
     * about in checkpointer, but we do have LWLocks, buffers, and temp
     * files.
     */
    LWLockReleaseAll();
    ConditionVariableCancelSleep();
    pgstat_report_wait_end();
    pgaio_error_cleanup();
    UnlockBuffers();
    ReleaseAuxProcessResources(false);
    AtEOXact_Buffers(false);
    AtEOXact_SMgr();
    AtEOXact_Files(false);
    AtEOXact_HashTables(false);

    /* Warn any waiting backends that the checkpoint failed. */
    if (ckpt_active)
    {
      SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
      CheckpointerShmem->ckpt_failed++;
      CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
      SpinLockRelease(&CheckpointerShmem->ckpt_lck);

      ConditionVariableBroadcast(&CheckpointerShmem->done_cv);

      ckpt_active = false;
    }

    /*
     * Now return to normal top-level context and clear ErrorContext for
     * next time.
     */
    MemoryContextSwitchTo(checkpointer_context);
    FlushErrorState();

    /* Flush any leaked data in the top-level context */
    MemoryContextReset(checkpointer_context);

    /* Now we can allow interrupts again */
    RESUME_INTERRUPTS();

    /*
     * Sleep at least 1 second after any error.  A write error is likely
     * to be repeated, and we don't want to be filling the error logs as
     * fast as we can.
     */
    pg_usleep(1000000L);
  }

  /* We can now handle ereport(ERROR) */
  PG_exception_stack = &local_sigjmp_buf;

  /*
   * Unblock signals (they were blocked when the postmaster forked us)
   */
  sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);

  /*
   * Ensure all shared memory values are set correctly for the config. Doing
   * this here ensures no race conditions from other concurrent updaters.
   */
  UpdateSharedMemoryConfig();

  /*
   * Advertise our proc number that backends can use to wake us up while
   * we're sleeping.
   */
  ProcGlobal->checkpointerProc = MyProcNumber;

  /*
   * Loop until we've been asked to write the shutdown checkpoint or
   * terminate.
   */
  for (;;)
  {
    bool    do_checkpoint = false;
    int     flags = 0;
    pg_time_t now;
    int     elapsed_secs;
    int     cur_timeout;
    bool    chkpt_or_rstpt_requested = false;
    bool    chkpt_or_rstpt_timed = false;

    /* Clear any already-pending wakeups */
    ResetLatch(MyLatch);

    /*
     * Process any requests or signals received recently.
     */
    AbsorbSyncRequests();

    ProcessCheckpointerInterrupts();
    if (ShutdownXLOGPending || ShutdownRequestPending)
      break;

    /*
     * Detect a pending checkpoint request by checking whether the flags
     * word in shared memory is nonzero.  We shouldn't need to acquire the
     * ckpt_lck for this.
     */
    if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
    {
      do_checkpoint = true;
      chkpt_or_rstpt_requested = true;
    }

    /*
     * Force a checkpoint if too much time has elapsed since the last one.
     * Note that we count a timed checkpoint in stats only when this
     * occurs without an external request, but we set the CAUSE_TIME flag
     * bit even if there is also an external request.
     */
    now = (pg_time_t) time(NULL);
    elapsed_secs = now - last_checkpoint_time;
    if (elapsed_secs >= CheckPointTimeout)
    {
      if (!do_checkpoint)
        chkpt_or_rstpt_timed = true;
      do_checkpoint = true;
      flags |= CHECKPOINT_CAUSE_TIME;
    }

    /*
     * Do a checkpoint if requested.
     */
    if (do_checkpoint)
    {
      bool    ckpt_performed = false;
      bool    do_restartpoint;

      /* Check if we should perform a checkpoint or a restartpoint. */
      do_restartpoint = RecoveryInProgress();

      /*
       * Atomically fetch the request flags to figure out what kind of a
       * checkpoint we should perform, and increase the started-counter
       * to acknowledge that we've started a new checkpoint.
       */
      SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
      flags |= CheckpointerShmem->ckpt_flags;
      CheckpointerShmem->ckpt_flags = 0;
      CheckpointerShmem->ckpt_started++;
      SpinLockRelease(&CheckpointerShmem->ckpt_lck);

      ConditionVariableBroadcast(&CheckpointerShmem->start_cv);

      /*
       * The end-of-recovery checkpoint is a real checkpoint that's
       * performed while we're still in recovery.
       */
      if (flags & CHECKPOINT_END_OF_RECOVERY)
        do_restartpoint = false;

      if (chkpt_or_rstpt_timed)
      {
        chkpt_or_rstpt_timed = false;
        if (do_restartpoint)
          PendingCheckpointerStats.restartpoints_timed++;
        else
          PendingCheckpointerStats.num_timed++;
      }

      if (chkpt_or_rstpt_requested)
      {
        chkpt_or_rstpt_requested = false;
        if (do_restartpoint)
          PendingCheckpointerStats.restartpoints_requested++;
        else
          PendingCheckpointerStats.num_requested++;
      }

      /*
       * We will warn if (a) too soon since last checkpoint (whatever
       * caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
       * since the last checkpoint start.  Note in particular that this
       * implementation will not generate warnings caused by
       * CheckPointTimeout < CheckPointWarning.
       */
      if (!do_restartpoint &&
        (flags & CHECKPOINT_CAUSE_XLOG) &&
        elapsed_secs < CheckPointWarning)
        ereport(LOG,
            (errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
                     "checkpoints are occurring too frequently (%d seconds apart)",
                     elapsed_secs,
                     elapsed_secs),
             errhint("Consider increasing the configuration parameter \"%s\".", "max_wal_size")));

      /*
       * Initialize checkpointer-private variables used during
       * checkpoint.
       */
      ckpt_active = true;
      if (do_restartpoint)
        ckpt_start_recptr = GetXLogReplayRecPtr(NULL);
      else
        ckpt_start_recptr = GetInsertRecPtr();
      ckpt_start_time = now;
      ckpt_cached_elapsed = 0;

      /*
       * Do the checkpoint.
       */
      if (!do_restartpoint)
        ckpt_performed = CreateCheckPoint(flags);
      else
        ckpt_performed = CreateRestartPoint(flags);

      /*
       * After any checkpoint, free all smgr objects.  Otherwise we
       * would never do so for dropped relations, as the checkpointer
       * does not process shared invalidation messages or call
       * AtEOXact_SMgr().
       */
      smgrdestroyall();

      /*
       * Indicate checkpoint completion to any waiting backends.
       */
      SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
      CheckpointerShmem->ckpt_done = CheckpointerShmem->ckpt_started;
      SpinLockRelease(&CheckpointerShmem->ckpt_lck);

      ConditionVariableBroadcast(&CheckpointerShmem->done_cv);

      if (!do_restartpoint)
      {
        /*
         * Note we record the checkpoint start time not end time as
         * last_checkpoint_time.  This is so that time-driven
         * checkpoints happen at a predictable spacing.
         */
        last_checkpoint_time = now;

        if (ckpt_performed)
          PendingCheckpointerStats.num_performed++;
      }
      else
      {
        if (ckpt_performed)
        {
          /*
           * The same as for checkpoint. Please see the
           * corresponding comment.
           */
          last_checkpoint_time = now;

          PendingCheckpointerStats.restartpoints_performed++;
        }
        else
        {
          /*
           * We were not able to perform the restartpoint
           * (checkpoints throw an ERROR in case of error).  Most
           * likely because we have not received any new checkpoint
           * WAL records since the last restartpoint. Try again in
           * 15 s.
           */
          last_checkpoint_time = now - CheckPointTimeout + 15;
        }
      }

      ckpt_active = false;

      /*
       * We may have received an interrupt during the checkpoint and the
       * latch might have been reset (e.g. in CheckpointWriteDelay).
       */
      ProcessCheckpointerInterrupts();
      if (ShutdownXLOGPending || ShutdownRequestPending)
        break;
    }

    /* Check for archive_timeout and switch xlog files if necessary. */
    CheckArchiveTimeout();

    /* Report pending statistics to the cumulative stats system */
    pgstat_report_checkpointer();
    pgstat_report_wal(true);

    /*
     * If any checkpoint flags have been set, redo the loop to handle the
     * checkpoint without sleeping.
     */
    if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
      continue;

    /*
     * Sleep until we are signaled or it's time for another checkpoint or
     * xlog file switch.
     */
    now = (pg_time_t) time(NULL);
    elapsed_secs = now - last_checkpoint_time;
    if (elapsed_secs >= CheckPointTimeout)
      continue;     /* no sleep for us ... */
    cur_timeout = CheckPointTimeout - elapsed_secs;
    if (XLogArchiveTimeout > 0 && !RecoveryInProgress())
    {
      elapsed_secs = now - last_xlog_switch_time;
      if (elapsed_secs >= XLogArchiveTimeout)
        continue;   /* no sleep for us ... */
      cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
    }

    (void) WaitLatch(MyLatch,
             WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
             cur_timeout * 1000L /* convert to ms */ ,
             WAIT_EVENT_CHECKPOINTER_MAIN);
  }

  /*
   * From here on, elog(ERROR) should end with exit(1), not send control
   * back to the sigsetjmp block above.
   */
  ExitOnAnyError = true;

  if (ShutdownXLOGPending)
  {
    /*
     * Close down the database.
     *
     * Since ShutdownXLOG() creates restartpoint or checkpoint, and
     * updates the statistics, increment the checkpoint request and flush
     * out pending statistic.
     */
    PendingCheckpointerStats.num_requested++;
    ShutdownXLOG(0, 0);
    pgstat_report_checkpointer();
    pgstat_report_wal(true);

    /*
     * Tell postmaster that we're done.
     */
    SendPostmasterSignal(PMSIGNAL_XLOG_IS_SHUTDOWN);
    ShutdownXLOGPending = false;
  }

  /*
   * Wait until we're asked to shut down. By separating the writing of the
   * shutdown checkpoint from checkpointer exiting, checkpointer can perform
   * some should-be-as-late-as-possible work like writing out stats.
   */
  for (;;)
  {
    /* Clear any already-pending wakeups */
    ResetLatch(MyLatch);

    ProcessCheckpointerInterrupts();

    if (ShutdownRequestPending)
      break;

    (void) WaitLatch(MyLatch,
             WL_LATCH_SET | WL_EXIT_ON_PM_DEATH,
             0,
             WAIT_EVENT_CHECKPOINTER_SHUTDOWN);
  }

  /* Normal exit from the checkpointer is here */
  proc_exit(0);       /* done */
}

/*
 * Process any new interrupts.
 */
static void
ProcessCheckpointerInterrupts(void)
{
  if (ProcSignalBarrierPending)
    ProcessProcSignalBarrier();

  if (ConfigReloadPending)
  {
    ConfigReloadPending = false;
    ProcessConfigFile(PGC_SIGHUP);

    /*
     * Checkpointer is the last process to shut down, so we ask it to hold
     * the keys for a range of other tasks required most of which have
     * nothing to do with checkpointing at all.
     *
     * For various reasons, some config values can change dynamically so
     * the primary copy of them is held in shared memory to make sure all
     * backends see the same value.  We make Checkpointer responsible for
     * updating the shared memory copy if the parameter setting changes
     * because of SIGHUP.
     */
    UpdateSharedMemoryConfig();
  }

  /* Perform logging of memory contexts of this process */
  if (LogMemoryContextPending)
    ProcessLogMemoryContextInterrupt();
}

/*
 * CheckArchiveTimeout -- check for archive_timeout and switch xlog files
 *
 * This will switch to a new WAL file and force an archive file write if
 * meaningful activity is recorded in the current WAL file. This includes most
 * writes, including just a single checkpoint record, but excludes WAL records
 * that were inserted with the XLOG_MARK_UNIMPORTANT flag being set (like
 * snapshots of running transactions).  Such records, depending on
 * configuration, occur on regular intervals and don't contain important
 * information.  This avoids generating archives with a few unimportant
 * records.
 */
static void
CheckArchiveTimeout(void)
{
  pg_time_t now;
  pg_time_t last_time;
  XLogRecPtr  last_switch_lsn;

  if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
    return;

  now = (pg_time_t) time(NULL);

  /* First we do a quick check using possibly-stale local state. */
  if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
    return;

  /*
   * Update local state ... note that last_xlog_switch_time is the last time
   * a switch was performed *or requested*.
   */
  last_time = GetLastSegSwitchData(&last_switch_lsn);

  last_xlog_switch_time = Max(last_xlog_switch_time, last_time);

  /* Now we can do the real checks */
  if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
  {
    /*
     * Switch segment only when "important" WAL has been logged since the
     * last segment switch (last_switch_lsn points to end of segment
     * switch occurred in).
     */
    if (GetLastImportantRecPtr() > last_switch_lsn)
    {
      XLogRecPtr  switchpoint;

      /* mark switch as unimportant, avoids triggering checkpoints */
      switchpoint = RequestXLogSwitch(true);

      /*
       * If the returned pointer points exactly to a segment boundary,
       * assume nothing happened.
       */
      if (XLogSegmentOffset(switchpoint, wal_segment_size) != 0)
        elog(DEBUG1, "write-ahead log switch forced (\"archive_timeout\"=%d)",
           XLogArchiveTimeout);
    }

    /*
     * Update state in any case, so we don't retry constantly when the
     * system is idle.
     */
    last_xlog_switch_time = now;
  }
}

/*
 * Returns true if a fast checkpoint request is pending.  (Note that this does
 * not check the *current* checkpoint's FAST flag, but whether there is one
 * pending behind it.)
 */
static bool
FastCheckpointRequested(void)
{
  volatile CheckpointerShmemStruct *cps = CheckpointerShmem;

  /*
   * We don't need to acquire the ckpt_lck in this case because we're only
   * looking at a single flag bit.
   */
  if (cps->ckpt_flags & CHECKPOINT_FAST)
    return true;
  return false;
}

/*
 * CheckpointWriteDelay -- control rate of checkpoint
 *
 * This function is called after each page write performed by BufferSync().
 * It is responsible for throttling BufferSync()'s write rate to hit
 * checkpoint_completion_target.
 *
 * The checkpoint request flags should be passed in; currently the only one
 * examined is CHECKPOINT_FAST, which disables delays between writes.
 *
 * 'progress' is an estimate of how much of the work has been done, as a
 * fraction between 0.0 meaning none, and 1.0 meaning all done.
 */
void
CheckpointWriteDelay(int flags, double progress)
{
  static int  absorb_counter = WRITES_PER_ABSORB;

  /* Do nothing if checkpoint is being executed by non-checkpointer process */
  if (!AmCheckpointerProcess())
    return;

  /*
   * Perform the usual duties and take a nap, unless we're behind schedule,
   * in which case we just try to catch up as quickly as possible.
   */
  if (!(flags & CHECKPOINT_FAST) &&
    !ShutdownXLOGPending &&
    !ShutdownRequestPending &&
    !FastCheckpointRequested() &&
    IsCheckpointOnSchedule(progress))
  {
    if (ConfigReloadPending)
    {
      ConfigReloadPending = false;
      ProcessConfigFile(PGC_SIGHUP);
      /* update shmem copies of config variables */
      UpdateSharedMemoryConfig();
    }

    AbsorbSyncRequests();
    absorb_counter = WRITES_PER_ABSORB;

    CheckArchiveTimeout();

    /* Report interim statistics to the cumulative stats system */
    pgstat_report_checkpointer();

    /*
     * This sleep used to be connected to bgwriter_delay, typically 200ms.
     * That resulted in more frequent wakeups if not much work to do.
     * Checkpointer and bgwriter are no longer related so take the Big
     * Sleep.
     */
    WaitLatch(MyLatch, WL_LATCH_SET | WL_EXIT_ON_PM_DEATH | WL_TIMEOUT,
          100,
          WAIT_EVENT_CHECKPOINT_WRITE_DELAY);
    ResetLatch(MyLatch);
  }
  else if (--absorb_counter <= 0)
  {
    /*
     * Absorb pending fsync requests after each WRITES_PER_ABSORB write
     * operations even when we don't sleep, to prevent overflow of the
     * fsync request queue.
     */
    AbsorbSyncRequests();
    absorb_counter = WRITES_PER_ABSORB;
  }

  /* Check for barrier events. */
  if (ProcSignalBarrierPending)
    ProcessProcSignalBarrier();
}

/*
 * IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
 *     (or restartpoint) in time?
 *
 * Compares the current progress against the time/segments elapsed since last
 * checkpoint, and returns true if the progress we've made this far is greater
 * than the elapsed time/segments.
 */
static bool
IsCheckpointOnSchedule(double progress)
{
  XLogRecPtr  recptr;
  struct timeval now;
  double    elapsed_xlogs,
        elapsed_time;

  Assert(ckpt_active);

  /* Scale progress according to checkpoint_completion_target. */
  progress *= CheckPointCompletionTarget;

  /*
   * Check against the cached value first. Only do the more expensive
   * calculations once we reach the target previously calculated. Since
   * neither time or WAL insert pointer moves backwards, a freshly
   * calculated value can only be greater than or equal to the cached value.
   */
  if (progress < ckpt_cached_elapsed)
    return false;

  /*
   * Check progress against WAL segments written and CheckPointSegments.
   *
   * We compare the current WAL insert location against the location
   * computed before calling CreateCheckPoint. The code in XLogInsert that
   * actually triggers a checkpoint when CheckPointSegments is exceeded
   * compares against RedoRecPtr, so this is not completely accurate.
   * However, it's good enough for our purposes, we're only calculating an
   * estimate anyway.
   *
   * During recovery, we compare last replayed WAL record's location with
   * the location computed before calling CreateRestartPoint. That maintains
   * the same pacing as we have during checkpoints in normal operation, but
   * we might exceed max_wal_size by a fair amount. That's because there can
   * be a large gap between a checkpoint's redo-pointer and the checkpoint
   * record itself, and we only start the restartpoint after we've seen the
   * checkpoint record. (The gap is typically up to CheckPointSegments *
   * checkpoint_completion_target where checkpoint_completion_target is the
   * value that was in effect when the WAL was generated).
   */
  if (RecoveryInProgress())
    recptr = GetXLogReplayRecPtr(NULL);
  else
    recptr = GetInsertRecPtr();
  elapsed_xlogs = (((double) (recptr - ckpt_start_recptr)) /
           wal_segment_size) / CheckPointSegments;

  if (progress < elapsed_xlogs)
  {
    ckpt_cached_elapsed = elapsed_xlogs;
    return false;
  }

  /*
   * Check progress against time elapsed and checkpoint_timeout.
   */
  gettimeofday(&now, NULL);
  elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
          now.tv_usec / 1000000.0) / CheckPointTimeout;

  if (progress < elapsed_time)
  {
    ckpt_cached_elapsed = elapsed_time;
    return false;
  }

  /* It looks like we're on schedule. */
  return true;
}


/* --------------------------------
 *    signal handler routines
 * --------------------------------
 */

/* SIGINT: set flag to trigger writing of shutdown checkpoint */
static void
ReqShutdownXLOG(SIGNAL_ARGS)
{
  ShutdownXLOGPending = true;
  SetLatch(MyLatch);
}


/* --------------------------------
 *    communication with backends
 * --------------------------------
 */

/*
 * CheckpointerShmemSize
 *    Compute space needed for checkpointer-related shared memory
 */
Size
CheckpointerShmemSize(void)
{
  Size    size;

  /*
   * The size of the requests[] array is arbitrarily set equal to NBuffers.
   * But there is a cap of MAX_CHECKPOINT_REQUESTS to prevent accumulating
   * too many checkpoint requests in the ring buffer.
   */
  size = offsetof(CheckpointerShmemStruct, requests);
  size = add_size(size, mul_size(Min(NBuffers,
                     MAX_CHECKPOINT_REQUESTS),
                   sizeof(CheckpointerRequest)));

  return size;
}

/*
 * CheckpointerShmemInit
 *    Allocate and initialize checkpointer-related shared memory
 */
void
CheckpointerShmemInit(void)
{
  Size    size = CheckpointerShmemSize();
  bool    found;

  CheckpointerShmem = (CheckpointerShmemStruct *)
    ShmemInitStruct("Checkpointer Data",
            size,
            &found);

  if (!found)
  {
    /*
     * First time through, so initialize.  Note that we zero the whole
     * requests array; this is so that CompactCheckpointerRequestQueue can
     * assume that any pad bytes in the request structs are zeroes.
     */
    MemSet(CheckpointerShmem, 0, size);
    SpinLockInit(&CheckpointerShmem->ckpt_lck);
    CheckpointerShmem->max_requests = Min(NBuffers, MAX_CHECKPOINT_REQUESTS);
    CheckpointerShmem->head = CheckpointerShmem->tail = 0;
    ConditionVariableInit(&CheckpointerShmem->start_cv);
    ConditionVariableInit(&CheckpointerShmem->done_cv);
  }
}

/*
 * ExecCheckpoint
 *    Primary entry point for manual CHECKPOINT commands
 *
 * This is mainly a wrapper for RequestCheckpoint().
 */
void
ExecCheckpoint(ParseState *pstate, CheckPointStmt *stmt)
{
  bool    fast = true;
  bool    unlogged = false;

  foreach_ptr(DefElem, opt, stmt->options)
  {
    if (strcmp(opt->defname, "mode") == 0)
    {
      char     *mode = defGetString(opt);

      if (strcmp(mode, "spread") == 0)
        fast = false;
      else if (strcmp(mode, "fast") != 0)
        ereport(ERROR,
            (errcode(ERRCODE_SYNTAX_ERROR),
             errmsg("unrecognized MODE option \"%s\"", mode),
             parser_errposition(pstate, opt->location)));
    }
    else if (strcmp(opt->defname, "flush_unlogged") == 0)
      unlogged = defGetBoolean(opt);
    else
      ereport(ERROR,
          (errcode(ERRCODE_SYNTAX_ERROR),
           errmsg("unrecognized CHECKPOINT option \"%s\"", opt->defname),
           parser_errposition(pstate, opt->location)));
  }

  if (!has_privs_of_role(GetUserId(), ROLE_PG_CHECKPOINT))
    ereport(ERROR,
        (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
    /* translator: %s is name of an SQL command (e.g., CHECKPOINT) */
         errmsg("permission denied to execute %s command",
            "CHECKPOINT"),
         errdetail("Only roles with privileges of the \"%s\" role may execute this command.",
               "pg_checkpoint")));

  RequestCheckpoint(CHECKPOINT_WAIT |
            (fast ? CHECKPOINT_FAST : 0) |
            (unlogged ? CHECKPOINT_FLUSH_UNLOGGED : 0) |
            (RecoveryInProgress() ? 0 : CHECKPOINT_FORCE));
}

/*
 * RequestCheckpoint
 *    Called in backend processes to request a checkpoint
 *
 * flags is a bitwise OR of the following:
 *  CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
 *  CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
 *  CHECKPOINT_FAST: finish the checkpoint ASAP,
 *    ignoring checkpoint_completion_target parameter.
 *  CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
 *    since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
 *    CHECKPOINT_END_OF_RECOVERY, and the CHECKPOINT command).
 *  CHECKPOINT_WAIT: wait for completion before returning (otherwise,
 *    just signal checkpointer to do it, and return).
 *  CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
 *    (This affects logging, and in particular enables CheckPointWarning.)
 */
void
RequestCheckpoint(int flags)
{
  int     ntries;
  int     old_failed,
        old_started;

  /*
   * If in a standalone backend, just do it ourselves.
   */
  if (!IsPostmasterEnvironment)
  {
    /*
     * There's no point in doing slow checkpoints in a standalone backend,
     * because there's no other backends the checkpoint could disrupt.
     */
    CreateCheckPoint(flags | CHECKPOINT_FAST);

    /* Free all smgr objects, as CheckpointerMain() normally would. */
    smgrdestroyall();

    return;
  }

  /*
   * Atomically set the request flags, and take a snapshot of the counters.
   * When we see ckpt_started > old_started, we know the flags we set here
   * have been seen by checkpointer.
   *
   * Note that we OR the flags with any existing flags, to avoid overriding
   * a "stronger" request by another backend.  The flag senses must be
   * chosen to make this work!
   */
  SpinLockAcquire(&CheckpointerShmem->ckpt_lck);

  old_failed = CheckpointerShmem->ckpt_failed;
  old_started = CheckpointerShmem->ckpt_started;
  CheckpointerShmem->ckpt_flags |= (flags | CHECKPOINT_REQUESTED);

  SpinLockRelease(&CheckpointerShmem->ckpt_lck);

  /*
   * Set checkpointer's latch to request checkpoint.  It's possible that the
   * checkpointer hasn't started yet, so we will retry a few times if
   * needed.  (Actually, more than a few times, since on slow or overloaded
   * buildfarm machines, it's been observed that the checkpointer can take
   * several seconds to start.)  However, if not told to wait for the
   * checkpoint to occur, we consider failure to set the latch to be
   * nonfatal and merely LOG it.  The checkpointer should see the request
   * when it does start, with or without the SetLatch().
   */
#define MAX_SIGNAL_TRIES 600  /* max wait 60.0 sec */
  for (ntries = 0;; ntries++)
  {
    volatile PROC_HDR *procglobal = ProcGlobal;
    ProcNumber  checkpointerProc = procglobal->checkpointerProc;

    if (checkpointerProc == INVALID_PROC_NUMBER)
    {
      if (ntries >= MAX_SIGNAL_TRIES || !(flags & CHECKPOINT_WAIT))
      {
        elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
           "could not notify checkpoint: checkpointer is not running");
        break;
      }
    }
    else
    {
      SetLatch(&GetPGProcByNumber(checkpointerProc)->procLatch);
      /* notified successfully */
      break;
    }

    CHECK_FOR_INTERRUPTS();
    pg_usleep(100000L);   /* wait 0.1 sec, then retry */
  }

  /*
   * If requested, wait for completion.  We detect completion according to
   * the algorithm given above.
   */
  if (flags & CHECKPOINT_WAIT)
  {
    int     new_started,
          new_failed;

    /* Wait for a new checkpoint to start. */
    ConditionVariablePrepareToSleep(&CheckpointerShmem->start_cv);
    for (;;)
    {
      SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
      new_started = CheckpointerShmem->ckpt_started;
      SpinLockRelease(&CheckpointerShmem->ckpt_lck);

      if (new_started != old_started)
        break;

      ConditionVariableSleep(&CheckpointerShmem->start_cv,
                   WAIT_EVENT_CHECKPOINT_START);
    }
    ConditionVariableCancelSleep();

    /*
     * We are waiting for ckpt_done >= new_started, in a modulo sense.
     */
    ConditionVariablePrepareToSleep(&CheckpointerShmem->done_cv);
    for (;;)
    {
      int     new_done;

      SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
      new_done = CheckpointerShmem->ckpt_done;
      new_failed = CheckpointerShmem->ckpt_failed;
      SpinLockRelease(&CheckpointerShmem->ckpt_lck);

      if (new_done - new_started >= 0)
        break;

      ConditionVariableSleep(&CheckpointerShmem->done_cv,
                   WAIT_EVENT_CHECKPOINT_DONE);
    }
    ConditionVariableCancelSleep();

    if (new_failed != old_failed)
      ereport(ERROR,
          (errmsg("checkpoint request failed"),
           errhint("Consult recent messages in the server log for details.")));
  }
}

/*
 * ForwardSyncRequest
 *    Forward a file-fsync request from a backend to the checkpointer
 *
 * Whenever a backend is compelled to write directly to a relation
 * (which should be seldom, if the background writer is getting its job done),
 * the backend calls this routine to pass over knowledge that the relation
 * is dirty and must be fsync'd before next checkpoint.  We also use this
 * opportunity to count such writes for statistical purposes.
 *
 * To avoid holding the lock for longer than necessary, we normally write
 * to the requests[] queue without checking for duplicates.  The checkpointer
 * will have to eliminate dups internally anyway.  However, if we discover
 * that the queue is full, we make a pass over the entire queue to compact
 * it.  This is somewhat expensive, but the alternative is for the backend
 * to perform its own fsync, which is far more expensive in practice.  It
 * is theoretically possible a backend fsync might still be necessary, if
 * the queue is full and contains no duplicate entries.  In that case, we
 * let the backend know by returning false.
 */
bool
ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
{
  CheckpointerRequest *request;
  bool    too_full;
  int     insert_pos;

  if (!IsUnderPostmaster)
    return false;     /* probably shouldn't even get here */

  if (AmCheckpointerProcess())
    elog(ERROR, "ForwardSyncRequest must not be called in checkpointer");

  LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);

  /*
   * If the checkpointer isn't running or the request queue is full, the
   * backend will have to perform its own fsync request.  But before forcing
   * that to happen, we can try to compact the request queue.
   */
  if (CheckpointerShmem->checkpointer_pid == 0 ||
    (CheckpointerShmem->num_requests >= CheckpointerShmem->max_requests &&
     !CompactCheckpointerRequestQueue()))
  {
    LWLockRelease(CheckpointerCommLock);
    return false;
  }

  /* OK, insert request */
  insert_pos = CheckpointerShmem->tail;
  request = &CheckpointerShmem->requests[insert_pos];
  request->ftag = *ftag;
  request->type = type;

  CheckpointerShmem->tail = (CheckpointerShmem->tail + 1) % CheckpointerShmem->max_requests;
  CheckpointerShmem->num_requests++;

  /* If queue is more than half full, nudge the checkpointer to empty it */
  too_full = (CheckpointerShmem->num_requests >=
        CheckpointerShmem->max_requests / 2);

  LWLockRelease(CheckpointerCommLock);

  /* ... but not till after we release the lock */
  if (too_full)
  {
    volatile PROC_HDR *procglobal = ProcGlobal;
    ProcNumber  checkpointerProc = procglobal->checkpointerProc;

    if (checkpointerProc != INVALID_PROC_NUMBER)
      SetLatch(&GetPGProcByNumber(checkpointerProc)->procLatch);
  }

  return true;
}

/*
 * CompactCheckpointerRequestQueue
 *    Remove duplicates from the request queue to avoid backend fsyncs.
 *    Returns "true" if any entries were removed.
 *
 * Although a full fsync request queue is not common, it can lead to severe
 * performance problems when it does happen.  So far, this situation has
 * only been observed to occur when the system is under heavy write load,
 * and especially during the "sync" phase of a checkpoint.  Without this
 * logic, each backend begins doing an fsync for every block written, which
 * gets very expensive and can slow down the whole system.
 *
 * Trying to do this every time the queue is full could lose if there
 * aren't any removable entries.  But that should be vanishingly rare in
 * practice: there's one queue entry per shared buffer.
 */
static bool
CompactCheckpointerRequestQueue(void)
{
  struct CheckpointerSlotMapping
  {
    CheckpointerRequest request;
    int     ring_idx;
  };

  int     n;
  int     num_skipped = 0;
  int     head;
  int     max_requests;
  int     num_requests;
  int     read_idx,
        write_idx;
  HASHCTL   ctl;
  HTAB     *htab;
  bool     *skip_slot;

  /* must hold CheckpointerCommLock in exclusive mode */
  Assert(LWLockHeldByMe(CheckpointerCommLock));

  /* Avoid memory allocations in a critical section. */
  if (CritSectionCount > 0)
    return false;

  max_requests = CheckpointerShmem->max_requests;
  num_requests = CheckpointerShmem->num_requests;

  /* Initialize skip_slot array */
  skip_slot = palloc0(sizeof(bool) * max_requests);

  head = CheckpointerShmem->head;

  /* Initialize temporary hash table */
  ctl.keysize = sizeof(CheckpointerRequest);
  ctl.entrysize = sizeof(struct CheckpointerSlotMapping);
  ctl.hcxt = CurrentMemoryContext;

  htab = hash_create("CompactCheckpointerRequestQueue",
             CheckpointerShmem->num_requests,
             &ctl,
             HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);

  /*
   * The basic idea here is that a request can be skipped if it's followed
   * by a later, identical request.  It might seem more sensible to work
   * backwards from the end of the queue and check whether a request is
   * *preceded* by an earlier, identical request, in the hopes of doing less
   * copying.  But that might change the semantics, if there's an
   * intervening SYNC_FORGET_REQUEST or SYNC_FILTER_REQUEST, so we do it
   * this way.  It would be possible to be even smarter if we made the code
   * below understand the specific semantics of such requests (it could blow
   * away preceding entries that would end up being canceled anyhow), but
   * it's not clear that the extra complexity would buy us anything.
   */
  read_idx = head;
  for (n = 0; n < num_requests; n++)
  {
    CheckpointerRequest *request;
    struct CheckpointerSlotMapping *slotmap;
    bool    found;

    /*
     * We use the request struct directly as a hashtable key.  This
     * assumes that any padding bytes in the structs are consistently the
     * same, which should be okay because we zeroed them in
     * CheckpointerShmemInit.  Note also that RelFileLocator had better
     * contain no pad bytes.
     */
    request = &CheckpointerShmem->requests[read_idx];
    slotmap = hash_search(htab, request, HASH_ENTER, &found);
    if (found)
    {
      /* Duplicate, so mark the previous occurrence as skippable */
      skip_slot[slotmap->ring_idx] = true;
      num_skipped++;
    }
    /* Remember slot containing latest occurrence of this request value */
    slotmap->ring_idx = read_idx;

    /* Move to the next request in the ring buffer */
    read_idx = (read_idx + 1) % max_requests;
  }

  /* Done with the hash table. */
  hash_destroy(htab);

  /* If no duplicates, we're out of luck. */
  if (!num_skipped)
  {
    pfree(skip_slot);
    return false;
  }

  /* We found some duplicates; remove them. */
  read_idx = write_idx = head;
  for (n = 0; n < num_requests; n++)
  {
    /* If this slot is NOT skipped, keep it */
    if (!skip_slot[read_idx])
    {
      /* If the read and write positions are different, copy the request */
      if (write_idx != read_idx)
        CheckpointerShmem->requests[write_idx] =
          CheckpointerShmem->requests[read_idx];

      /* Advance the write position */
      write_idx = (write_idx + 1) % max_requests;
    }

    read_idx = (read_idx + 1) % max_requests;
  }

  /*
   * Update ring buffer state: head remains the same, tail moves, count
   * decreases
   */
  CheckpointerShmem->tail = write_idx;
  CheckpointerShmem->num_requests -= num_skipped;

  ereport(DEBUG1,
      (errmsg_internal("compacted fsync request queue from %d entries to %d entries",
               num_requests, CheckpointerShmem->num_requests)));

  /* Cleanup. */
  pfree(skip_slot);
  return true;
}

/*
 * AbsorbSyncRequests
 *    Retrieve queued sync requests and pass them to sync mechanism.
 *
 * This is exported because it must be called during CreateCheckPoint;
 * we have to be sure we have accepted all pending requests just before
 * we start fsync'ing.  Since CreateCheckPoint sometimes runs in
 * non-checkpointer processes, do nothing if not checkpointer.
 */
void
AbsorbSyncRequests(void)
{
  CheckpointerRequest *requests = NULL;
  CheckpointerRequest *request;
  int     n,
        i;
  bool    loop;

  if (!AmCheckpointerProcess())
    return;

  do
  {
    LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);

    /*---
     * We try to avoid holding the lock for a long time by:
     * 1. Copying the request array and processing the requests after
     *    releasing the lock;
     * 2. Processing not the whole queue, but only batches of
     *    CKPT_REQ_BATCH_SIZE at once.
     *
     * Once we have cleared the requests from shared memory, we must
     * PANIC if we then fail to absorb them (e.g., because our hashtable
     * runs out of memory).  This is because the system cannot run safely
     * if we are unable to fsync what we have been told to fsync.
     * Fortunately, the hashtable is so small that the problem is quite
     * unlikely to arise in practice.
     *
     * Note: The maximum possible size of a ring buffer is
     * MAX_CHECKPOINT_REQUESTS entries, which fit into a maximum palloc
     * allocation size of 1Gb.  Our maximum batch size,
     * CKPT_REQ_BATCH_SIZE, is even smaller.
     */
    n = Min(CheckpointerShmem->num_requests, CKPT_REQ_BATCH_SIZE);
    if (n > 0)
    {
      if (!requests)
        requests = (CheckpointerRequest *) palloc(n * sizeof(CheckpointerRequest));

      for (i = 0; i < n; i++)
      {
        requests[i] = CheckpointerShmem->requests[CheckpointerShmem->head];
        CheckpointerShmem->head = (CheckpointerShmem->head + 1) % CheckpointerShmem->max_requests;
      }

      CheckpointerShmem->num_requests -= n;

    }

    START_CRIT_SECTION();

    /* Are there any requests in the queue? If so, keep going. */
    loop = CheckpointerShmem->num_requests != 0;

    LWLockRelease(CheckpointerCommLock);

    for (request = requests; n > 0; request++, n--)
      RememberSyncRequest(&request->ftag, request->type);

    END_CRIT_SECTION();
  } while (loop);

  if (requests)
    pfree(requests);
}

/*
 * Update any shared memory configurations based on config parameters
 */
static void
UpdateSharedMemoryConfig(void)
{
  /* update global shmem state for sync rep */
  SyncRepUpdateSyncStandbysDefined();

  /*
   * If full_page_writes has been changed by SIGHUP, we update it in shared
   * memory and write an XLOG_FPW_CHANGE record.
   */
  UpdateFullPageWrites();

  elog(DEBUG2, "checkpointer updated shared memory configuration values");
}

/*
 * FirstCallSinceLastCheckpoint allows a process to take an action once
 * per checkpoint cycle by asynchronously checking for checkpoint completion.
 */
bool
FirstCallSinceLastCheckpoint(void)
{
  static int  ckpt_done = 0;
  int     new_done;
  bool    FirstCall = false;

  SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
  new_done = CheckpointerShmem->ckpt_done;
  SpinLockRelease(&CheckpointerShmem->ckpt_lck);

  if (new_done != ckpt_done)
    FirstCall = true;

  ckpt_done = new_done;

  return FirstCall;
}

Coverage Report

Created: 2025-09-27 06:52