/src/postgres/src/backend/storage/ipc/standby.c

Source
/*-------------------------------------------------------------------------
 *
 * standby.c
 *    Misc functions used in Hot Standby mode.
 *
 *  All functions for handling RM_STANDBY_ID, which relate to
 *  AccessExclusiveLocks and starting snapshots for Hot Standby mode.
 *  Plus conflict recovery processing.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/storage/ipc/standby.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "access/xloginsert.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/slot.h"
#include "storage/bufmgr.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/sinvaladt.h"
#include "storage/standby.h"
#include "utils/hsearch.h"
#include "utils/injection_point.h"
#include "utils/ps_status.h"
#include "utils/timeout.h"
#include "utils/timestamp.h"
#include "utils/wait_event.h"

/* User-settable GUC parameters */
int     max_standby_archive_delay = 30 * 1000;
int     max_standby_streaming_delay = 30 * 1000;
bool    log_recovery_conflict_waits = false;

/*
 * Keep track of all the exclusive locks owned by original transactions.
 * For each known exclusive lock, there is a RecoveryLockEntry in the
 * RecoveryLockHash hash table.  All RecoveryLockEntrys belonging to a
 * given XID are chained together so that we can find them easily.
 * For each original transaction that is known to have any such locks,
 * there is a RecoveryLockXidEntry in the RecoveryLockXidHash hash table,
 * which stores the head of the chain of its locks.
 */
typedef struct RecoveryLockEntry
{
  xl_standby_lock key;    /* hash key: xid, dbOid, relOid */
  struct RecoveryLockEntry *next; /* chain link */
} RecoveryLockEntry;

typedef struct RecoveryLockXidEntry
{
  TransactionId xid;      /* hash key -- must be first */
  struct RecoveryLockEntry *head; /* chain head */
} RecoveryLockXidEntry;

static HTAB *RecoveryLockHash = NULL;
static HTAB *RecoveryLockXidHash = NULL;

/* Flags set by timeout handlers */
static volatile sig_atomic_t got_standby_deadlock_timeout = false;
static volatile sig_atomic_t got_standby_delay_timeout = false;
static volatile sig_atomic_t got_standby_lock_timeout = false;

static void ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
                           RecoveryConflictReason reason,
                           uint32 wait_event_info,
                           bool report_waiting);
static void SendRecoveryConflictWithBufferPin(RecoveryConflictReason reason);
static XLogRecPtr LogCurrentRunningXacts(RunningTransactions CurrRunningXacts);
static void LogAccessExclusiveLocks(int nlocks, xl_standby_lock *locks);
static const char *get_recovery_conflict_desc(RecoveryConflictReason reason);

/*
 * InitRecoveryTransactionEnvironment
 *    Initialize tracking of our primary's in-progress transactions.
 *
 * We need to issue shared invalidations and hold locks. Holding locks
 * means others may want to wait on us, so we need to make a lock table
 * vxact entry like a real transaction. We could create and delete
 * lock table entries for each transaction but its simpler just to create
 * one permanent entry and leave it there all the time. Locks are then
 * acquired and released as needed. Yes, this means you can see the
 * Startup process in pg_locks once we have run this.
 */
void
InitRecoveryTransactionEnvironment(void)
{
  VirtualTransactionId vxid;
  HASHCTL   hash_ctl;

  Assert(RecoveryLockHash == NULL); /* don't run this twice */

  /*
   * Initialize the hash tables for tracking the locks held by each
   * transaction.
   */
  hash_ctl.keysize = sizeof(xl_standby_lock);
  hash_ctl.entrysize = sizeof(RecoveryLockEntry);
  RecoveryLockHash = hash_create("RecoveryLockHash",
                   64,
                   &hash_ctl,
                   HASH_ELEM | HASH_BLOBS);
  hash_ctl.keysize = sizeof(TransactionId);
  hash_ctl.entrysize = sizeof(RecoveryLockXidEntry);
  RecoveryLockXidHash = hash_create("RecoveryLockXidHash",
                    64,
                    &hash_ctl,
                    HASH_ELEM | HASH_BLOBS);

  /*
   * Initialize shared invalidation management for Startup process, being
   * careful to register ourselves as a sendOnly process so we don't need to
   * read messages, nor will we get signaled when the queue starts filling
   * up.
   */
  SharedInvalBackendInit(true);

  /*
   * Lock a virtual transaction id for Startup process.
   *
   * We need to do GetNextLocalTransactionId() because
   * SharedInvalBackendInit() leaves localTransactionId invalid and the lock
   * manager doesn't like that at all.
   *
   * Note that we don't need to run XactLockTableInsert() because nobody
   * needs to wait on xids. That sounds a little strange, but table locks
   * are held by vxids and row level locks are held by xids. All queries
   * hold AccessShareLocks so never block while we write or lock new rows.
   */
  MyProc->vxid.procNumber = MyProcNumber;
  vxid.procNumber = MyProcNumber;
  vxid.localTransactionId = GetNextLocalTransactionId();
  VirtualXactLockTableInsert(vxid);

  standbyState = STANDBY_INITIALIZED;
}

/*
 * ShutdownRecoveryTransactionEnvironment
 *    Shut down transaction tracking
 *
 * Prepare to switch from hot standby mode to normal operation. Shut down
 * recovery-time transaction tracking.
 *
 * This must be called even in shutdown of startup process if transaction
 * tracking has been initialized. Otherwise some locks the tracked
 * transactions were holding will not be released and may interfere with
 * the processes still running (but will exit soon later) at the exit of
 * startup process.
 */
void
ShutdownRecoveryTransactionEnvironment(void)
{
  /*
   * Do nothing if RecoveryLockHash is NULL because that means that
   * transaction tracking has not yet been initialized or has already been
   * shut down.  This makes it safe to have possibly-redundant calls of this
   * function during process exit.
   */
  if (RecoveryLockHash == NULL)
    return;

  /* Mark all tracked in-progress transactions as finished. */
  ExpireAllKnownAssignedTransactionIds();

  /* Release all locks the tracked transactions were holding */
  StandbyReleaseAllLocks();

  /* Destroy the lock hash tables. */
  hash_destroy(RecoveryLockHash);
  hash_destroy(RecoveryLockXidHash);
  RecoveryLockHash = NULL;
  RecoveryLockXidHash = NULL;

  /* Cleanup our VirtualTransaction */
  VirtualXactLockTableCleanup();
}


/*
 * -----------------------------------------------------
 *    Standby wait timers and backend cancel logic
 * -----------------------------------------------------
 */

/*
 * Determine the cutoff time at which we want to start canceling conflicting
 * transactions.  Returns zero (a time safely in the past) if we are willing
 * to wait forever.
 */
static TimestampTz
GetStandbyLimitTime(void)
{
  TimestampTz rtime;
  bool    fromStream;

  /*
   * The cutoff time is the last WAL data receipt time plus the appropriate
   * delay variable.  Delay of -1 means wait forever.
   */
  GetXLogReceiptTime(&rtime, &fromStream);
  if (fromStream)
  {
    if (max_standby_streaming_delay < 0)
      return 0;     /* wait forever */
    return TimestampTzPlusMilliseconds(rtime, max_standby_streaming_delay);
  }
  else
  {
    if (max_standby_archive_delay < 0)
      return 0;     /* wait forever */
    return TimestampTzPlusMilliseconds(rtime, max_standby_archive_delay);
  }
}

#define STANDBY_INITIAL_WAIT_US  1000
static int  standbyWait_us = STANDBY_INITIAL_WAIT_US;

/*
 * Standby wait logic for ResolveRecoveryConflictWithVirtualXIDs.
 * We wait here for a while then return. If we decide we can't wait any
 * more then we return true, if we can wait some more return false.
 */
static bool
WaitExceedsMaxStandbyDelay(uint32 wait_event_info)
{
  TimestampTz ltime;

  CHECK_FOR_INTERRUPTS();

  /* Are we past the limit time? */
  ltime = GetStandbyLimitTime();
  if (ltime && GetCurrentTimestamp() >= ltime)
    return true;

  /*
   * Sleep a bit (this is essential to avoid busy-waiting).
   */
  pgstat_report_wait_start(wait_event_info);
  pg_usleep(standbyWait_us);
  pgstat_report_wait_end();

  /*
   * Progressively increase the sleep times, but not to more than 1s, since
   * pg_usleep isn't interruptible on some platforms.
   */
  standbyWait_us *= 2;
  if (standbyWait_us > 1000000)
    standbyWait_us = 1000000;

  return false;
}

/*
 * Log the recovery conflict.
 *
 * wait_start is the timestamp when the caller started to wait.
 * now is the timestamp when this function has been called.
 * wait_list is the list of virtual transaction ids assigned to
 * conflicting processes. still_waiting indicates whether
 * the startup process is still waiting for the recovery conflict
 * to be resolved or not.
 */
void
LogRecoveryConflict(RecoveryConflictReason reason, TimestampTz wait_start,
          TimestampTz now, VirtualTransactionId *wait_list,
          bool still_waiting)
{
  long    secs;
  int     usecs;
  long    msecs;
  StringInfoData buf;
  int     nprocs = 0;

  /*
   * There must be no conflicting processes when the recovery conflict has
   * already been resolved.
   */
  Assert(still_waiting || wait_list == NULL);

  TimestampDifference(wait_start, now, &secs, &usecs);
  msecs = secs * 1000 + usecs / 1000;
  usecs = usecs % 1000;

  if (wait_list)
  {
    VirtualTransactionId *vxids;

    /* Construct a string of list of the conflicting processes */
    vxids = wait_list;
    while (VirtualTransactionIdIsValid(*vxids))
    {
      PGPROC     *proc = ProcNumberGetProc(vxids->procNumber);

      /* proc can be NULL if the target backend is not active */
      if (proc)
      {
        if (nprocs == 0)
        {
          initStringInfo(&buf);
          appendStringInfo(&buf, "%d", proc->pid);
        }
        else
          appendStringInfo(&buf, ", %d", proc->pid);

        nprocs++;
      }

      vxids++;
    }
  }

  /*
   * If wait_list is specified, report the list of PIDs of active
   * conflicting backends in a detail message. Note that if all the backends
   * in the list are not active, no detail message is logged.
   */
  if (still_waiting)
  {
    ereport(LOG,
        errmsg("recovery still waiting after %ld.%03d ms: %s",
             msecs, usecs, get_recovery_conflict_desc(reason)),
        nprocs > 0 ? errdetail_log_plural("Conflicting process: %s.",
                          "Conflicting processes: %s.",
                          nprocs, buf.data) : 0);
  }
  else
  {
    ereport(LOG,
        errmsg("recovery finished waiting after %ld.%03d ms: %s",
             msecs, usecs, get_recovery_conflict_desc(reason)));
  }

  if (nprocs > 0)
    pfree(buf.data);
}

/*
 * This is the main executioner for any query backend that conflicts with
 * recovery processing. Judgement has already been passed on it within
 * a specific rmgr. Here we just issue the orders to the procs. The procs
 * then throw the required error as instructed.
 *
 * If report_waiting is true, "waiting" is reported in PS display and the
 * wait for recovery conflict is reported in the log, if necessary. If
 * the caller is responsible for reporting them, report_waiting should be
 * false. Otherwise, both the caller and this function report the same
 * thing unexpectedly.
 */
static void
ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist,
                     RecoveryConflictReason reason,
                     uint32 wait_event_info,
                     bool report_waiting)
{
  TimestampTz waitStart = 0;
  bool    waiting = false;
  bool    logged_recovery_conflict = false;

  /* Fast exit, to avoid a kernel call if there's no work to be done. */
  if (!VirtualTransactionIdIsValid(*waitlist))
    return;

  /* Set the wait start timestamp for reporting */
  if (report_waiting && (log_recovery_conflict_waits || update_process_title))
    waitStart = GetCurrentTimestamp();

  while (VirtualTransactionIdIsValid(*waitlist))
  {
    /* reset standbyWait_us for each xact we wait for */
    standbyWait_us = STANDBY_INITIAL_WAIT_US;

    /* wait until the virtual xid is gone */
    while (!VirtualXactLock(*waitlist, false))
    {
      /* Is it time to kill it? */
      if (WaitExceedsMaxStandbyDelay(wait_event_info))
      {
        bool    signaled;

        /*
         * Now find out who to throw out of the balloon.
         */
        Assert(VirtualTransactionIdIsValid(*waitlist));
        signaled = SignalRecoveryConflictWithVirtualXID(*waitlist, reason);

        /*
         * Wait a little bit for it to die so that we avoid flooding
         * an unresponsive backend when system is heavily loaded.
         */
        if (signaled)
          pg_usleep(5000L);
      }

      if (waitStart != 0 && (!logged_recovery_conflict || !waiting))
      {
        TimestampTz now = 0;
        bool    maybe_log_conflict;
        bool    maybe_update_title;

        maybe_log_conflict = (log_recovery_conflict_waits && !logged_recovery_conflict);
        maybe_update_title = (update_process_title && !waiting);

        /* Get the current timestamp if not report yet */
        if (maybe_log_conflict || maybe_update_title)
          now = GetCurrentTimestamp();

        /*
         * Report via ps if we have been waiting for more than 500
         * msec (should that be configurable?)
         */
        if (maybe_update_title &&
          TimestampDifferenceExceeds(waitStart, now, 500))
        {
          set_ps_display_suffix("waiting");
          waiting = true;
        }

        /*
         * Emit the log message if the startup process is waiting
         * longer than deadlock_timeout for recovery conflict.
         */
        if (maybe_log_conflict &&
          TimestampDifferenceExceeds(waitStart, now, DeadlockTimeout))
        {
          LogRecoveryConflict(reason, waitStart, now, waitlist, true);
          logged_recovery_conflict = true;
        }
      }
    }

    /* The virtual transaction is gone now, wait for the next one */
    waitlist++;
  }

  /*
   * Emit the log message if recovery conflict was resolved but the startup
   * process waited longer than deadlock_timeout for it.
   */
  if (logged_recovery_conflict)
    LogRecoveryConflict(reason, waitStart, GetCurrentTimestamp(),
              NULL, false);

  /* reset ps display to remove the suffix if we added one */
  if (waiting)
    set_ps_display_remove_suffix();

}

/*
 * Generate whatever recovery conflicts are needed to eliminate snapshots that
 * might see XIDs <= snapshotConflictHorizon as still running.
 *
 * snapshotConflictHorizon cutoffs are our standard approach to generating
 * granular recovery conflicts.  Note that InvalidTransactionId values are
 * interpreted as "definitely don't need any conflicts" here, which is a
 * general convention that WAL records can (and often do) depend on.
 */
void
ResolveRecoveryConflictWithSnapshot(TransactionId snapshotConflictHorizon,
                  bool isCatalogRel,
                  RelFileLocator locator)
{
  VirtualTransactionId *backends;

  /*
   * If we get passed InvalidTransactionId then we do nothing (no conflict).
   *
   * This can happen whenever the changes in the WAL record do not affect
   * visibility on a standby. For example: a record that only freezes an
   * xmax from a locker.
   *
   * It's also quite common with records generated during index deletion
   * (original execution of the deletion can reason that a recovery conflict
   * which is sufficient for the deletion operation must take place before
   * replay of the deletion record itself).
   */
  if (!TransactionIdIsValid(snapshotConflictHorizon))
    return;

  Assert(TransactionIdIsNormal(snapshotConflictHorizon));
  backends = GetConflictingVirtualXIDs(snapshotConflictHorizon,
                     locator.dbOid);
  ResolveRecoveryConflictWithVirtualXIDs(backends,
                       RECOVERY_CONFLICT_SNAPSHOT,
                       WAIT_EVENT_RECOVERY_CONFLICT_SNAPSHOT,
                       true);

  /*
   * Note that WaitExceedsMaxStandbyDelay() is not taken into account here
   * (as opposed to ResolveRecoveryConflictWithVirtualXIDs() above). That
   * seems OK, given that this kind of conflict should not normally be
   * reached, e.g. due to using a physical replication slot.
   */
  if (IsLogicalDecodingEnabled() && isCatalogRel)
    InvalidateObsoleteReplicationSlots(RS_INVAL_HORIZON, 0, locator.dbOid,
                       snapshotConflictHorizon);
}

/*
 * Variant of ResolveRecoveryConflictWithSnapshot that works with
 * FullTransactionId values
 */
void
ResolveRecoveryConflictWithSnapshotFullXid(FullTransactionId snapshotConflictHorizon,
                       bool isCatalogRel,
                       RelFileLocator locator)
{
  /*
   * ResolveRecoveryConflictWithSnapshot operates on 32-bit TransactionIds,
   * so truncate the logged FullTransactionId.  If the logged value is very
   * old, so that XID wrap-around already happened on it, there can't be any
   * snapshots that still see it.
   */
  FullTransactionId nextXid = ReadNextFullTransactionId();
  uint64    diff;

  diff = U64FromFullTransactionId(nextXid) -
    U64FromFullTransactionId(snapshotConflictHorizon);
  if (diff < MaxTransactionId / 2)
  {
    TransactionId truncated;

    truncated = XidFromFullTransactionId(snapshotConflictHorizon);
    ResolveRecoveryConflictWithSnapshot(truncated,
                      isCatalogRel,
                      locator);
  }
}

void
ResolveRecoveryConflictWithTablespace(Oid tsid)
{
  VirtualTransactionId *temp_file_users;

  /*
   * Standby users may be currently using this tablespace for their
   * temporary files. We only care about current users because
   * temp_tablespace parameter will just ignore tablespaces that no longer
   * exist.
   *
   * Ask everybody to cancel their queries immediately so we can ensure no
   * temp files remain and we can remove the tablespace. Nuke the entire
   * site from orbit, it's the only way to be sure.
   *
   * XXX: We could work out the pids of active backends using this
   * tablespace by examining the temp filenames in the directory. We would
   * then convert the pids into VirtualXIDs before attempting to cancel
   * them.
   *
   * We don't wait for commit because drop tablespace is non-transactional.
   */
  temp_file_users = GetConflictingVirtualXIDs(InvalidTransactionId,
                        InvalidOid);
  ResolveRecoveryConflictWithVirtualXIDs(temp_file_users,
                       RECOVERY_CONFLICT_TABLESPACE,
                       WAIT_EVENT_RECOVERY_CONFLICT_TABLESPACE,
                       true);
}

void
ResolveRecoveryConflictWithDatabase(Oid dbid)
{
  /*
   * We don't do ResolveRecoveryConflictWithVirtualXIDs() here since that
   * only waits for transactions and completely idle sessions would block
   * us. This is rare enough that we do this as simply as possible: no wait,
   * just force them off immediately.
   *
   * No locking is required here because we already acquired
   * AccessExclusiveLock. Anybody trying to connect while we do this will
   * block during InitPostgres() and then disconnect when they see the
   * database has been removed.
   */
  while (CountDBBackends(dbid) > 0)
  {
    SignalRecoveryConflictWithDatabase(dbid, RECOVERY_CONFLICT_DATABASE);

    /*
     * Wait awhile for them to die so that we avoid flooding an
     * unresponsive backend when system is heavily loaded.
     */
    pg_usleep(10000);
  }
}

/*
 * ResolveRecoveryConflictWithLock is called from ProcSleep()
 * to resolve conflicts with other backends holding relation locks.
 *
 * The WaitLatch sleep normally done in ProcSleep()
 * (when not InHotStandby) is performed here, for code clarity.
 *
 * We either resolve conflicts immediately or set a timeout to wake us at
 * the limit of our patience.
 *
 * Resolve conflicts by canceling to all backends holding a conflicting
 * lock.  As we are already queued to be granted the lock, no new lock
 * requests conflicting with ours will be granted in the meantime.
 *
 * We also must check for deadlocks involving the Startup process and
 * hot-standby backend processes. If deadlock_timeout is reached in
 * this function, all the backends holding the conflicting locks are
 * requested to check themselves for deadlocks.
 *
 * logging_conflict should be true if the recovery conflict has not been
 * logged yet even though logging is enabled. After deadlock_timeout is
 * reached and the request for deadlock check is sent, we wait again to
 * be signaled by the release of the lock if logging_conflict is false.
 * Otherwise we return without waiting again so that the caller can report
 * the recovery conflict. In this case, then, this function is called again
 * with logging_conflict=false (because the recovery conflict has already
 * been logged) and we will wait again for the lock to be released.
 */
void
ResolveRecoveryConflictWithLock(LOCKTAG locktag, bool logging_conflict)
{
  TimestampTz ltime;
  TimestampTz now;

  Assert(InHotStandby);

  ltime = GetStandbyLimitTime();
  now = GetCurrentTimestamp();

  /*
   * Update waitStart if first time through after the startup process
   * started waiting for the lock. It should not be updated every time
   * ResolveRecoveryConflictWithLock() is called during the wait.
   *
   * Use the current time obtained for comparison with ltime as waitStart
   * (i.e., the time when this process started waiting for the lock). Since
   * getting the current time newly can cause overhead, we reuse the
   * already-obtained time to avoid that overhead.
   *
   * Note that waitStart is updated without holding the lock table's
   * partition lock, to avoid the overhead by additional lock acquisition.
   * This can cause "waitstart" in pg_locks to become NULL for a very short
   * period of time after the wait started even though "granted" is false.
   * This is OK in practice because we can assume that users are likely to
   * look at "waitstart" when waiting for the lock for a long time.
   */
  if (pg_atomic_read_u64(&MyProc->waitStart) == 0)
    pg_atomic_write_u64(&MyProc->waitStart, now);

  if (now >= ltime && ltime != 0)
  {
    /*
     * We're already behind, so clear a path as quickly as possible.
     */
    VirtualTransactionId *backends;

    backends = GetLockConflicts(&locktag, AccessExclusiveLock, NULL);

    /*
     * Prevent ResolveRecoveryConflictWithVirtualXIDs() from reporting
     * "waiting" in PS display by disabling its argument report_waiting
     * because the caller, WaitOnLock(), has already reported that.
     */
    ResolveRecoveryConflictWithVirtualXIDs(backends,
                         RECOVERY_CONFLICT_LOCK,
                         PG_WAIT_LOCK | locktag.locktag_type,
                         false);
  }
  else
  {
    /*
     * Wait (or wait again) until ltime, and check for deadlocks as well
     * if we will be waiting longer than deadlock_timeout
     */
    EnableTimeoutParams timeouts[2];
    int     cnt = 0;

    if (ltime != 0)
    {
      got_standby_lock_timeout = false;
      timeouts[cnt].id = STANDBY_LOCK_TIMEOUT;
      timeouts[cnt].type = TMPARAM_AT;
      timeouts[cnt].fin_time = ltime;
      cnt++;
    }

    got_standby_deadlock_timeout = false;
    timeouts[cnt].id = STANDBY_DEADLOCK_TIMEOUT;
    timeouts[cnt].type = TMPARAM_AFTER;
    timeouts[cnt].delay_ms = DeadlockTimeout;
    cnt++;

    enable_timeouts(timeouts, cnt);
  }

  /* Wait to be signaled by the release of the Relation Lock */
  ProcWaitForSignal(PG_WAIT_LOCK | locktag.locktag_type);

  /*
   * Exit if ltime is reached. Then all the backends holding conflicting
   * locks will be canceled in the next ResolveRecoveryConflictWithLock()
   * call.
   */
  if (got_standby_lock_timeout)
    goto cleanup;

  if (got_standby_deadlock_timeout)
  {
    VirtualTransactionId *backends;

    backends = GetLockConflicts(&locktag, AccessExclusiveLock, NULL);

    /* Quick exit if there's no work to be done */
    if (!VirtualTransactionIdIsValid(*backends))
      goto cleanup;

    /*
     * Send signals to all the backends holding the conflicting locks, to
     * ask them to check themselves for deadlocks.
     */
    while (VirtualTransactionIdIsValid(*backends))
    {
      (void) SignalRecoveryConflictWithVirtualXID(*backends,
                            RECOVERY_CONFLICT_STARTUP_DEADLOCK);
      backends++;
    }

    /*
     * Exit if the recovery conflict has not been logged yet even though
     * logging is enabled, so that the caller can log that. Then
     * RecoveryConflictWithLock() is called again and we will wait again
     * for the lock to be released.
     */
    if (logging_conflict)
      goto cleanup;

    /*
     * Wait again here to be signaled by the release of the Relation Lock,
     * to prevent the subsequent RecoveryConflictWithLock() from causing
     * deadlock_timeout and sending a request for deadlocks check again.
     * Otherwise the request continues to be sent every deadlock_timeout
     * until the relation locks are released or ltime is reached.
     */
    got_standby_deadlock_timeout = false;
    ProcWaitForSignal(PG_WAIT_LOCK | locktag.locktag_type);
  }

cleanup:

  /*
   * Clear any timeout requests established above.  We assume here that the
   * Startup process doesn't have any other outstanding timeouts than those
   * used by this function. If that stops being true, we could cancel the
   * timeouts individually, but that'd be slower.
   */
  disable_all_timeouts(false);
  got_standby_lock_timeout = false;
  got_standby_deadlock_timeout = false;
}

/*
 * ResolveRecoveryConflictWithBufferPin is called from LockBufferForCleanup()
 * to resolve conflicts with other backends holding buffer pins.
 *
 * The ProcWaitForSignal() sleep normally done in LockBufferForCleanup()
 * (when not InHotStandby) is performed here, for code clarity.
 *
 * We either resolve conflicts immediately or set a timeout to wake us at
 * the limit of our patience.
 *
 * Resolve conflicts by sending a PROCSIG signal to all backends to check if
 * they hold one of the buffer pins that is blocking Startup process. If so,
 * those backends will take an appropriate error action, ERROR or FATAL.
 *
 * We also must check for deadlocks.  Deadlocks occur because if queries
 * wait on a lock, that must be behind an AccessExclusiveLock, which can only
 * be cleared if the Startup process replays a transaction completion record.
 * If Startup process is also waiting then that is a deadlock. The deadlock
 * can occur if the query is waiting and then the Startup sleeps, or if
 * Startup is sleeping and the query waits on a lock. We protect against
 * only the former sequence here, the latter sequence is checked prior to
 * the query sleeping, in CheckRecoveryConflictDeadlock().
 *
 * Deadlocks are extremely rare, and relatively expensive to check for,
 * so we don't do a deadlock check right away ... only if we have had to wait
 * at least deadlock_timeout.
 */
void
ResolveRecoveryConflictWithBufferPin(void)
{
  TimestampTz ltime;

  Assert(InHotStandby);

  ltime = GetStandbyLimitTime();

  if (GetCurrentTimestamp() >= ltime && ltime != 0)
  {
    /*
     * We're already behind, so clear a path as quickly as possible.
     */
    SendRecoveryConflictWithBufferPin(RECOVERY_CONFLICT_BUFFERPIN);
  }
  else
  {
    /*
     * Wake up at ltime, and check for deadlocks as well if we will be
     * waiting longer than deadlock_timeout
     */
    EnableTimeoutParams timeouts[2];
    int     cnt = 0;

    if (ltime != 0)
    {
      timeouts[cnt].id = STANDBY_TIMEOUT;
      timeouts[cnt].type = TMPARAM_AT;
      timeouts[cnt].fin_time = ltime;
      cnt++;
    }

    got_standby_deadlock_timeout = false;
    timeouts[cnt].id = STANDBY_DEADLOCK_TIMEOUT;
    timeouts[cnt].type = TMPARAM_AFTER;
    timeouts[cnt].delay_ms = DeadlockTimeout;
    cnt++;

    enable_timeouts(timeouts, cnt);
  }

  /*
   * Wait to be signaled by UnpinBuffer() or for the wait to be interrupted
   * by one of the timeouts established above.
   *
   * We assume that only UnpinBuffer() and the timeout requests established
   * above can wake us up here. WakeupRecovery() called by walreceiver or
   * SIGHUP signal handler, etc cannot do that because it uses the different
   * latch from that ProcWaitForSignal() waits on.
   */
  ProcWaitForSignal(WAIT_EVENT_BUFFER_CLEANUP);

  if (got_standby_delay_timeout)
    SendRecoveryConflictWithBufferPin(RECOVERY_CONFLICT_BUFFERPIN);
  else if (got_standby_deadlock_timeout)
  {
    /*
     * Send out a request for hot-standby backends to check themselves for
     * deadlocks.
     *
     * XXX The subsequent ResolveRecoveryConflictWithBufferPin() will wait
     * to be signaled by UnpinBuffer() again and send a request for
     * deadlocks check if deadlock_timeout happens. This causes the
     * request to continue to be sent every deadlock_timeout until the
     * buffer is unpinned or ltime is reached. This would increase the
     * workload in the startup process and backends. In practice it may
     * not be so harmful because the period that the buffer is kept pinned
     * is basically no so long. But we should fix this?
     */
    SendRecoveryConflictWithBufferPin(RECOVERY_CONFLICT_BUFFERPIN_DEADLOCK);
  }

  /*
   * Clear any timeout requests established above.  We assume here that the
   * Startup process doesn't have any other timeouts than what this function
   * uses.  If that stops being true, we could cancel the timeouts
   * individually, but that'd be slower.
   */
  disable_all_timeouts(false);
  got_standby_delay_timeout = false;
  got_standby_deadlock_timeout = false;
}

static void
SendRecoveryConflictWithBufferPin(RecoveryConflictReason reason)
{
  Assert(reason == RECOVERY_CONFLICT_BUFFERPIN ||
       reason == RECOVERY_CONFLICT_BUFFERPIN_DEADLOCK);

  /*
   * We send signal to all backends to ask them if they are holding the
   * buffer pin which is delaying the Startup process. Most of them will be
   * innocent, but we let the SIGUSR1 handling in each backend decide their
   * own fate.
   */
  SignalRecoveryConflictWithDatabase(InvalidOid, reason);
}

/*
 * In Hot Standby perform early deadlock detection.  We abort the lock
 * wait if we are about to sleep while holding the buffer pin that Startup
 * process is waiting for.
 *
 * Note: this code is pessimistic, because there is no way for it to
 * determine whether an actual deadlock condition is present: the lock we
 * need to wait for might be unrelated to any held by the Startup process.
 * Sooner or later, this mechanism should get ripped out in favor of somehow
 * accounting for buffer locks in DeadLockCheck().  However, errors here
 * seem to be very low-probability in practice, so for now it's not worth
 * the trouble.
 */
void
CheckRecoveryConflictDeadlock(void)
{
  Assert(!InRecovery);    /* do not call in Startup process */

  if (!HoldingBufferPinThatDelaysRecovery())
    return;

  /*
   * Error message should match ProcessInterrupts() but we avoid calling
   * that because we aren't handling an interrupt at this point. Note that
   * we only cancel the current transaction here, so if we are in a
   * subtransaction and the pin is held by a parent, then the Startup
   * process will continue to wait even though we have avoided deadlock.
   */
  ereport(ERROR,
      (errcode(ERRCODE_T_R_DEADLOCK_DETECTED),
       errmsg("canceling statement due to conflict with recovery"),
       errdetail("User transaction caused buffer deadlock with recovery.")));
}


/* --------------------------------
 *    timeout handler routines
 * --------------------------------
 */

/*
 * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT is
 * exceeded.
 */
void
StandbyDeadLockHandler(void)
{
  got_standby_deadlock_timeout = true;
}

/*
 * StandbyTimeoutHandler() will be called if STANDBY_TIMEOUT is exceeded.
 */
void
StandbyTimeoutHandler(void)
{
  got_standby_delay_timeout = true;
}

/*
 * StandbyLockTimeoutHandler() will be called if STANDBY_LOCK_TIMEOUT is exceeded.
 */
void
StandbyLockTimeoutHandler(void)
{
  got_standby_lock_timeout = true;
}

/*
 * -----------------------------------------------------
 * Locking in Recovery Mode
 * -----------------------------------------------------
 *
 * All locks are held by the Startup process using a single virtual
 * transaction. This implementation is both simpler and in some senses,
 * more correct. The locks held mean "some original transaction held
 * this lock, so query access is not allowed at this time". So the Startup
 * process is the proxy by which the original locks are implemented.
 *
 * We only keep track of AccessExclusiveLocks, which are only ever held by
 * one transaction on one relation.
 *
 * We keep a table of known locks in the RecoveryLockHash hash table.
 * The point of that table is to let us efficiently de-duplicate locks,
 * which is important because checkpoints will re-report the same locks
 * already held.  There is also a RecoveryLockXidHash table with one entry
 * per xid, which allows us to efficiently find all the locks held by a
 * given original transaction.
 *
 * We use session locks rather than normal locks so we don't need
 * ResourceOwners.
 */


void
StandbyAcquireAccessExclusiveLock(TransactionId xid, Oid dbOid, Oid relOid)
{
  RecoveryLockXidEntry *xidentry;
  RecoveryLockEntry *lockentry;
  xl_standby_lock key;
  LOCKTAG   locktag;
  bool    found;

  /* Already processed? */
  if (!TransactionIdIsValid(xid) ||
    TransactionIdDidCommit(xid) ||
    TransactionIdDidAbort(xid))
    return;

  elog(DEBUG4, "adding recovery lock: db %u rel %u", dbOid, relOid);

  /* dbOid is InvalidOid when we are locking a shared relation. */
  Assert(OidIsValid(relOid));

  /* Create a hash entry for this xid, if we don't have one already. */
  xidentry = hash_search(RecoveryLockXidHash, &xid, HASH_ENTER, &found);
  if (!found)
  {
    Assert(xidentry->xid == xid); /* dynahash should have set this */
    xidentry->head = NULL;
  }

  /* Create a hash entry for this lock, unless we have one already. */
  key.xid = xid;
  key.dbOid = dbOid;
  key.relOid = relOid;
  lockentry = hash_search(RecoveryLockHash, &key, HASH_ENTER, &found);
  if (!found)
  {
    /* First, acquire the lock ... */
    SET_LOCKTAG_RELATION(locktag, dbOid, relOid);

    (void) LockAcquire(&locktag, AccessExclusiveLock, true, false);

    /* ... and then, as it is new, link it into the XID's list. */
    lockentry->next = xidentry->head;
    xidentry->head = lockentry;
  }
}

/*
 * Release all the locks associated with this RecoveryLockXidEntry.
 */
static void
StandbyReleaseXidEntryLocks(RecoveryLockXidEntry *xidentry)
{
  RecoveryLockEntry *entry;
  RecoveryLockEntry *next;

  for (entry = xidentry->head; entry != NULL; entry = next)
  {
    LOCKTAG   locktag;

    elog(DEBUG4,
       "releasing recovery lock: xid %u db %u rel %u",
       entry->key.xid, entry->key.dbOid, entry->key.relOid);
    /* Release the lock ... */
    SET_LOCKTAG_RELATION(locktag, entry->key.dbOid, entry->key.relOid);
    if (!LockRelease(&locktag, AccessExclusiveLock, true))
    {
      elog(LOG,
         "RecoveryLockHash contains entry for lock no longer recorded by lock manager: xid %u database %u relation %u",
         entry->key.xid, entry->key.dbOid, entry->key.relOid);
      Assert(false);
    }
    /* ... and remove the per-lock hash entry */
    next = entry->next;
    hash_search(RecoveryLockHash, entry, HASH_REMOVE, NULL);
  }

  xidentry->head = NULL;    /* just for paranoia */
}

/*
 * Release locks for specific XID, or all locks if it's InvalidXid.
 */
static void
StandbyReleaseLocks(TransactionId xid)
{
  RecoveryLockXidEntry *entry;

  if (TransactionIdIsValid(xid))
  {
    if ((entry = hash_search(RecoveryLockXidHash, &xid, HASH_FIND, NULL)))
    {
      StandbyReleaseXidEntryLocks(entry);
      hash_search(RecoveryLockXidHash, entry, HASH_REMOVE, NULL);
    }
  }
  else
    StandbyReleaseAllLocks();
}

/*
 * Release locks for a transaction tree, starting at xid down, from
 * RecoveryLockXidHash.
 *
 * Called during WAL replay of COMMIT/ROLLBACK when in hot standby mode,
 * to remove any AccessExclusiveLocks requested by a transaction.
 */
void
StandbyReleaseLockTree(TransactionId xid, int nsubxids, TransactionId *subxids)
{
  int     i;

  StandbyReleaseLocks(xid);

  for (i = 0; i < nsubxids; i++)
    StandbyReleaseLocks(subxids[i]);
}

/*
 * Called at end of recovery and when we see a shutdown checkpoint.
 */
void
StandbyReleaseAllLocks(void)
{
  HASH_SEQ_STATUS status;
  RecoveryLockXidEntry *entry;

  elog(DEBUG2, "release all standby locks");

  hash_seq_init(&status, RecoveryLockXidHash);
  while ((entry = hash_seq_search(&status)))
  {
    StandbyReleaseXidEntryLocks(entry);
    hash_search(RecoveryLockXidHash, entry, HASH_REMOVE, NULL);
  }
}

/*
 * StandbyReleaseOldLocks
 *    Release standby locks held by top-level XIDs that aren't running,
 *    as long as they're not prepared transactions.
 *
 * This is needed to prune the locks of crashed transactions, which didn't
 * write an ABORT/COMMIT record.
 */
void
StandbyReleaseOldLocks(TransactionId oldxid)
{
  HASH_SEQ_STATUS status;
  RecoveryLockXidEntry *entry;

  hash_seq_init(&status, RecoveryLockXidHash);
  while ((entry = hash_seq_search(&status)))
  {
    Assert(TransactionIdIsValid(entry->xid));

    /* Skip if prepared transaction. */
    if (StandbyTransactionIdIsPrepared(entry->xid))
      continue;

    /* Skip if >= oldxid. */
    if (!TransactionIdPrecedes(entry->xid, oldxid))
      continue;

    /* Remove all locks and hash table entry. */
    StandbyReleaseXidEntryLocks(entry);
    hash_search(RecoveryLockXidHash, entry, HASH_REMOVE, NULL);
  }
}

/*
 * --------------------------------------------------------------------
 *    Recovery handling for Rmgr RM_STANDBY_ID
 *
 * These record types will only be created if XLogStandbyInfoActive()
 * --------------------------------------------------------------------
 */

void
standby_redo(XLogReaderState *record)
{
  uint8   info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;

  /* Backup blocks are not used in standby records */
  Assert(!XLogRecHasAnyBlockRefs(record));

  /* Do nothing if we're not in hot standby mode */
  if (standbyState == STANDBY_DISABLED)
    return;

  if (info == XLOG_STANDBY_LOCK)
  {
    xl_standby_locks *xlrec = (xl_standby_locks *) XLogRecGetData(record);
    int     i;

    for (i = 0; i < xlrec->nlocks; i++)
      StandbyAcquireAccessExclusiveLock(xlrec->locks[i].xid,
                        xlrec->locks[i].dbOid,
                        xlrec->locks[i].relOid);
  }
  else if (info == XLOG_RUNNING_XACTS)
  {
    xl_running_xacts *xlrec = (xl_running_xacts *) XLogRecGetData(record);
    RunningTransactionsData running;

    running.xcnt = xlrec->xcnt;
    running.subxcnt = xlrec->subxcnt;
    running.subxid_status = xlrec->subxid_overflow ? SUBXIDS_MISSING : SUBXIDS_IN_ARRAY;
    running.nextXid = xlrec->nextXid;
    running.latestCompletedXid = xlrec->latestCompletedXid;
    running.oldestRunningXid = xlrec->oldestRunningXid;
    running.xids = xlrec->xids;

    ProcArrayApplyRecoveryInfo(&running);

    /*
     * The startup process currently has no convenient way to schedule
     * stats to be reported. XLOG_RUNNING_XACTS records issued at a
     * regular cadence, making this a convenient location to report stats.
     * While these records aren't generated with wal_level=minimal, stats
     * also cannot be accessed during WAL replay.
     */
    pgstat_report_stat(true);
  }
  else if (info == XLOG_INVALIDATIONS)
  {
    xl_invalidations *xlrec = (xl_invalidations *) XLogRecGetData(record);

    ProcessCommittedInvalidationMessages(xlrec->msgs,
                       xlrec->nmsgs,
                       xlrec->relcacheInitFileInval,
                       xlrec->dbId,
                       xlrec->tsId);
  }
  else
    elog(PANIC, "standby_redo: unknown op code %u", info);
}

/*
 * Log details of the current snapshot to WAL. This allows the snapshot state
 * to be reconstructed on the standby and for logical decoding.
 *
 * This is used for Hot Standby as follows:
 *
 * We can move directly to STANDBY_SNAPSHOT_READY at startup if we
 * start from a shutdown checkpoint because we know nothing was running
 * at that time and our recovery snapshot is known empty. In the more
 * typical case of an online checkpoint we need to jump through a few
 * hoops to get a correct recovery snapshot and this requires a two or
 * sometimes a three stage process.
 *
 * The initial snapshot must contain all running xids and all current
 * AccessExclusiveLocks at a point in time on the standby. Assembling
 * that information while the server is running requires many and
 * various LWLocks, so we choose to derive that information piece by
 * piece and then re-assemble that info on the standby. When that
 * information is fully assembled we move to STANDBY_SNAPSHOT_READY.
 *
 * Since locking on the primary when we derive the information is not
 * strict, we note that there is a time window between the derivation and
 * writing to WAL of the derived information. That allows race conditions
 * that we must resolve, since xids and locks may enter or leave the
 * snapshot during that window. This creates the issue that an xid or
 * lock may start *after* the snapshot has been derived yet *before* the
 * snapshot is logged in the running xacts WAL record. We resolve this by
 * starting to accumulate changes at a point just prior to when we derive
 * the snapshot on the primary, then ignore duplicates when we later apply
 * the snapshot from the running xacts record. This is implemented during
 * CreateCheckPoint() where we use the logical checkpoint location as
 * our starting point and then write the running xacts record immediately
 * before writing the main checkpoint WAL record. Since we always start
 * up from a checkpoint and are immediately at our starting point, we
 * unconditionally move to STANDBY_INITIALIZED. After this point we
 * must do 4 things:
 *  * move shared nextXid forwards as we see new xids
 *  * extend the clog and subtrans with each new xid
 *  * keep track of uncommitted known assigned xids
 *  * keep track of uncommitted AccessExclusiveLocks
 *
 * When we see a commit/abort we must remove known assigned xids and locks
 * from the completing transaction. Attempted removals that cannot locate
 * an entry are expected and must not cause an error when we are in state
 * STANDBY_INITIALIZED. This is implemented in StandbyReleaseLocks() and
 * KnownAssignedXidsRemove().
 *
 * Later, when we apply the running xact data we must be careful to ignore
 * transactions already committed, since those commits raced ahead when
 * making WAL entries.
 *
 * For logical decoding only the running xacts information is needed;
 * there's no need to look at the locking information, but it's logged anyway,
 * as there's no independent knob to just enable logical decoding. For
 * details of how this is used, check snapbuild.c's introductory comment.
 *
 *
 * Returns the RecPtr of the last inserted record.
 */
XLogRecPtr
LogStandbySnapshot(void)
{
  XLogRecPtr  recptr;
  RunningTransactions running;
  xl_standby_lock *locks;
  int     nlocks;
  bool    logical_decoding_enabled = IsLogicalDecodingEnabled();

  Assert(XLogStandbyInfoActive());

#ifdef USE_INJECTION_POINTS
  if (IS_INJECTION_POINT_ATTACHED("skip-log-running-xacts"))
  {
    /*
     * This record could move slot's xmin forward during decoding, leading
     * to unpredictable results, so skip it when requested by the test.
     */
    return GetInsertRecPtr();
  }
#endif

  /*
   * Get details of any AccessExclusiveLocks being held at the moment.
   */
  locks = GetRunningTransactionLocks(&nlocks);
  if (nlocks > 0)
    LogAccessExclusiveLocks(nlocks, locks);
  pfree(locks);

  /*
   * Log details of all in-progress transactions. This should be the last
   * record we write, because standby will open up when it sees this.
   */
  running = GetRunningTransactionData();

  /*
   * GetRunningTransactionData() acquired ProcArrayLock, we must release it.
   * For Hot Standby this can be done before inserting the WAL record
   * because ProcArrayApplyRecoveryInfo() rechecks the commit status using
   * the clog. For logical decoding, though, the lock can't be released
   * early because the clog might be "in the future" from the POV of the
   * historic snapshot. This would allow for situations where we're waiting
   * for the end of a transaction listed in the xl_running_xacts record
   * which, according to the WAL, has committed before the xl_running_xacts
   * record. Fortunately this routine isn't executed frequently, and it's
   * only a shared lock.
   */
  if (!logical_decoding_enabled)
    LWLockRelease(ProcArrayLock);

  recptr = LogCurrentRunningXacts(running);

  /* Release lock if we kept it longer ... */
  if (logical_decoding_enabled)
    LWLockRelease(ProcArrayLock);

  /* GetRunningTransactionData() acquired XidGenLock, we must release it */
  LWLockRelease(XidGenLock);

  return recptr;
}

/*
 * Record an enhanced snapshot of running transactions into WAL.
 *
 * The definitions of RunningTransactionsData and xl_running_xacts are
 * similar. We keep them separate because xl_running_xacts is a contiguous
 * chunk of memory and never exists fully until it is assembled in WAL.
 * The inserted records are marked as not being important for durability,
 * to avoid triggering superfluous checkpoint / archiving activity.
 */
static XLogRecPtr
LogCurrentRunningXacts(RunningTransactions CurrRunningXacts)
{
  xl_running_xacts xlrec;
  XLogRecPtr  recptr;

  xlrec.xcnt = CurrRunningXacts->xcnt;
  xlrec.subxcnt = CurrRunningXacts->subxcnt;
  xlrec.subxid_overflow = (CurrRunningXacts->subxid_status != SUBXIDS_IN_ARRAY);
  xlrec.nextXid = CurrRunningXacts->nextXid;
  xlrec.oldestRunningXid = CurrRunningXacts->oldestRunningXid;
  xlrec.latestCompletedXid = CurrRunningXacts->latestCompletedXid;

  /* Header */
  XLogBeginInsert();
  XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT);
  XLogRegisterData(&xlrec, MinSizeOfXactRunningXacts);

  /* array of TransactionIds */
  if (xlrec.xcnt > 0)
    XLogRegisterData(CurrRunningXacts->xids,
             (xlrec.xcnt + xlrec.subxcnt) * sizeof(TransactionId));

  recptr = XLogInsert(RM_STANDBY_ID, XLOG_RUNNING_XACTS);

  if (xlrec.subxid_overflow)
    elog(DEBUG2,
       "snapshot of %d running transactions overflowed (lsn %X/%08X oldest xid %u latest complete %u next xid %u)",
       CurrRunningXacts->xcnt,
       LSN_FORMAT_ARGS(recptr),
       CurrRunningXacts->oldestRunningXid,
       CurrRunningXacts->latestCompletedXid,
       CurrRunningXacts->nextXid);
  else
    elog(DEBUG2,
       "snapshot of %d+%d running transaction ids (lsn %X/%08X oldest xid %u latest complete %u next xid %u)",
       CurrRunningXacts->xcnt, CurrRunningXacts->subxcnt,
       LSN_FORMAT_ARGS(recptr),
       CurrRunningXacts->oldestRunningXid,
       CurrRunningXacts->latestCompletedXid,
       CurrRunningXacts->nextXid);

  /*
   * Ensure running_xacts information is synced to disk not too far in the
   * future. We don't want to stall anything though (i.e. use XLogFlush()),
   * so we let the wal writer do it during normal operation.
   * XLogSetAsyncXactLSN() conveniently will mark the LSN as to-be-synced
   * and nudge the WALWriter into action if sleeping. Check
   * XLogBackgroundFlush() for details why a record might not be flushed
   * without it.
   */
  XLogSetAsyncXactLSN(recptr);

  return recptr;
}

/*
 * Wholesale logging of AccessExclusiveLocks. Other lock types need not be
 * logged, as described in backend/storage/lmgr/README.
 */
static void
LogAccessExclusiveLocks(int nlocks, xl_standby_lock *locks)
{
  xl_standby_locks xlrec;

  xlrec.nlocks = nlocks;

  XLogBeginInsert();
  XLogRegisterData(&xlrec, offsetof(xl_standby_locks, locks));
  XLogRegisterData(locks, nlocks * sizeof(xl_standby_lock));
  XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT);

  (void) XLogInsert(RM_STANDBY_ID, XLOG_STANDBY_LOCK);
}

/*
 * Individual logging of AccessExclusiveLocks for use during LockAcquire()
 */
void
LogAccessExclusiveLock(Oid dbOid, Oid relOid)
{
  xl_standby_lock xlrec;

  xlrec.xid = GetCurrentTransactionId();

  xlrec.dbOid = dbOid;
  xlrec.relOid = relOid;

  LogAccessExclusiveLocks(1, &xlrec);
  MyXactFlags |= XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK;
}

/*
 * Prepare to log an AccessExclusiveLock, for use during LockAcquire()
 */
void
LogAccessExclusiveLockPrepare(void)
{
  /*
   * Ensure that a TransactionId has been assigned to this transaction, for
   * two reasons, both related to lock release on the standby. First, we
   * must assign an xid so that RecordTransactionCommit() and
   * RecordTransactionAbort() do not optimise away the transaction
   * completion record which recovery relies upon to release locks. It's a
   * hack, but for a corner case not worth adding code for into the main
   * commit path. Second, we must assign an xid before the lock is recorded
   * in shared memory, otherwise a concurrently executing
   * GetRunningTransactionLocks() might see a lock associated with an
   * InvalidTransactionId which we later assert cannot happen.
   */
  (void) GetCurrentTransactionId();
}

/*
 * Emit WAL for invalidations. This currently is only used for commits without
 * an xid but which contain invalidations.
 */
void
LogStandbyInvalidations(int nmsgs, SharedInvalidationMessage *msgs,
            bool relcacheInitFileInval)
{
  xl_invalidations xlrec;

  /* prepare record */
  memset(&xlrec, 0, sizeof(xlrec));
  xlrec.dbId = MyDatabaseId;
  xlrec.tsId = MyDatabaseTableSpace;
  xlrec.relcacheInitFileInval = relcacheInitFileInval;
  xlrec.nmsgs = nmsgs;

  /* perform insertion */
  XLogBeginInsert();
  XLogRegisterData(&xlrec, MinSizeOfInvalidations);
  XLogRegisterData(msgs,
           nmsgs * sizeof(SharedInvalidationMessage));
  XLogInsert(RM_STANDBY_ID, XLOG_INVALIDATIONS);
}

/* Return the description of recovery conflict */
static const char *
get_recovery_conflict_desc(RecoveryConflictReason reason)
{
  const char *reasonDesc = _("unknown reason");

  switch (reason)
  {
    case RECOVERY_CONFLICT_BUFFERPIN:
      reasonDesc = _("recovery conflict on buffer pin");
      break;
    case RECOVERY_CONFLICT_LOCK:
      reasonDesc = _("recovery conflict on lock");
      break;
    case RECOVERY_CONFLICT_TABLESPACE:
      reasonDesc = _("recovery conflict on tablespace");
      break;
    case RECOVERY_CONFLICT_SNAPSHOT:
      reasonDesc = _("recovery conflict on snapshot");
      break;
    case RECOVERY_CONFLICT_LOGICALSLOT:
      reasonDesc = _("recovery conflict on replication slot");
      break;
    case RECOVERY_CONFLICT_STARTUP_DEADLOCK:
      reasonDesc = _("recovery conflict on deadlock");
      break;
    case RECOVERY_CONFLICT_BUFFERPIN_DEADLOCK:
      reasonDesc = _("recovery conflict on buffer deadlock");
      break;
    case RECOVERY_CONFLICT_DATABASE:
      reasonDesc = _("recovery conflict on database");
      break;
  }

  return reasonDesc;
}

Coverage Report

Created: 2026-10-16 06:48