xlogfuncs.c

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/*-------------------------------------------------------------------------
 *
 * xlogfuncs.c
 *
 * PostgreSQL write-ahead log manager user interface functions
 *
 * This file contains WAL control and information functions.
 *
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/access/transam/xlogfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <unistd.h>
 
#include "access/htup_details.h"
#include "access/xlog_internal.h"
#include "access/xlogbackup.h"
#include "access/xlogrecovery.h"
#include "catalog/pg_type.h"
#include "commands/waitlsn.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walreceiver.h"
#include "storage/fd.h"
#include "storage/proc.h"
#include "storage/standby.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/pg_lsn.h"
#include "utils/snapmgr.h"
#include "utils/timestamp.h"
 
/*
 * Backup-related variables.
 */
static BackupState *backup_state = NULL;
static StringInfo tablespace_map = NULL;
 
/* Session-level context for the SQL-callable backup functions */
static MemoryContext backupcontext = NULL;
 
/*
 * pg_backup_start: set up for taking an on-line backup dump
 *
 * Essentially what this does is to create the contents required for the
 * backup_label file and the tablespace map.
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_backup_start(PG_FUNCTION_ARGS)
{
    text       *backupid = PG_GETARG_TEXT_PP(0);
    bool        fast = PG_GETARG_BOOL(1);
    char       *backupidstr;
    SessionBackupState status = get_backup_status();
    MemoryContext oldcontext;
 
    backupidstr = text_to_cstring(backupid);
 
    if (status == SESSION_BACKUP_RUNNING)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("a backup is already in progress in this session")));
 
    /*
     * backup_state and tablespace_map need to be long-lived as they are used
     * in pg_backup_stop().  These are allocated in a dedicated memory context
     * child of TopMemoryContext, deleted at the end of pg_backup_stop().  If
     * an error happens before ending the backup, memory would be leaked in
     * this context until pg_backup_start() is called again.
     */
    if (backupcontext == NULL)
    {
        backupcontext = AllocSetContextCreate(TopMemoryContext,
                                              "on-line backup context",
                                              ALLOCSET_START_SMALL_SIZES);
    }
    else
    {
        backup_state = NULL;
        tablespace_map = NULL;
        MemoryContextReset(backupcontext);
    }
 
    oldcontext = MemoryContextSwitchTo(backupcontext);
    backup_state = (BackupState *) palloc0(sizeof(BackupState));
    tablespace_map = makeStringInfo();
    MemoryContextSwitchTo(oldcontext);
 
    register_persistent_abort_backup_handler();
    do_pg_backup_start(backupidstr, fast, NULL, backup_state, tablespace_map);
 
    PG_RETURN_LSN(backup_state->startpoint);
}
 
 
/*
 * pg_backup_stop: finish taking an on-line backup.
 *
 * The first parameter (variable 'waitforarchive'), which is optional,
 * allows the user to choose if they want to wait for the WAL to be archived
 * or if we should just return as soon as the WAL record is written.
 *
 * This function stops an in-progress backup, creates backup_label contents and
 * it returns the backup stop LSN, backup_label and tablespace_map contents.
 *
 * The backup_label contains the user-supplied label string (typically this
 * would be used to tell where the backup dump will be stored), the starting
 * time, starting WAL location for the dump and so on.  It is the caller's
 * responsibility to write the backup_label and tablespace_map files in the
 * data folder that will be restored from this backup.
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_backup_stop(PG_FUNCTION_ARGS)
{
#define PG_BACKUP_STOP_V2_COLS 3
    TupleDesc   tupdesc;
    Datum       values[PG_BACKUP_STOP_V2_COLS] = {0};
    bool        nulls[PG_BACKUP_STOP_V2_COLS] = {0};
    bool        waitforarchive = PG_GETARG_BOOL(0);
    char       *backup_label;
    SessionBackupState status = get_backup_status();
 
    /* Initialize attributes information in the tuple descriptor */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    if (status != SESSION_BACKUP_RUNNING)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("backup is not in progress"),
                 errhint("Did you call pg_backup_start()?")));
 
    Assert(backup_state != NULL);
    Assert(tablespace_map != NULL);
 
    /* Stop the backup */
    do_pg_backup_stop(backup_state, waitforarchive);
 
    /* Build the contents of backup_label */
    backup_label = build_backup_content(backup_state, false);
 
    values[0] = LSNGetDatum(backup_state->stoppoint);
    values[1] = CStringGetTextDatum(backup_label);
    values[2] = CStringGetTextDatum(tablespace_map->data);
 
    /* Deallocate backup-related variables */
    pfree(backup_label);
 
    /* Clean up the session-level state and its memory context */
    backup_state = NULL;
    tablespace_map = NULL;
    MemoryContextDelete(backupcontext);
    backupcontext = NULL;
 
    /* Returns the record as Datum */
    PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
}
 
/*
 * pg_switch_wal: switch to next xlog file
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_switch_wal(PG_FUNCTION_ARGS)
{
    XLogRecPtr  switchpoint;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("WAL control functions cannot be executed during recovery.")));
 
    switchpoint = RequestXLogSwitch(false);
 
    /*
     * As a convenience, return the WAL location of the switch record
     */
    PG_RETURN_LSN(switchpoint);
}
 
/*
 * pg_log_standby_snapshot: call LogStandbySnapshot()
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_log_standby_snapshot(PG_FUNCTION_ARGS)
{
    XLogRecPtr  recptr;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("%s cannot be executed during recovery.",
                         "pg_log_standby_snapshot()")));
 
    if (!XLogStandbyInfoActive())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("pg_log_standby_snapshot() can only be used if \"wal_level\" >= \"replica\"")));
 
    recptr = LogStandbySnapshot();
 
    /*
     * As a convenience, return the WAL location of the last inserted record
     */
    PG_RETURN_LSN(recptr);
}
 
/*
 * pg_create_restore_point: a named point for restore
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_create_restore_point(PG_FUNCTION_ARGS)
{
    text       *restore_name = PG_GETARG_TEXT_PP(0);
    char       *restore_name_str;
    XLogRecPtr  restorepoint;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("WAL control functions cannot be executed during recovery.")));
 
    if (!XLogIsNeeded())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("WAL level not sufficient for creating a restore point"),
                 errhint("\"wal_level\" must be set to \"replica\" or \"logical\" at server start.")));
 
    restore_name_str = text_to_cstring(restore_name);
 
    if (strlen(restore_name_str) >= MAXFNAMELEN)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("value too long for restore point (maximum %d characters)", MAXFNAMELEN - 1)));
 
    restorepoint = XLogRestorePoint(restore_name_str);
 
    /*
     * As a convenience, return the WAL location of the restore point record
     */
    PG_RETURN_LSN(restorepoint);
}
 
/*
 * Report the current WAL write location (same format as pg_backup_start etc)
 *
 * This is useful for determining how much of WAL is visible to an external
 * archiving process.  Note that the data before this point is written out
 * to the kernel, but is not necessarily synced to disk.
 */
Datum
pg_current_wal_lsn(PG_FUNCTION_ARGS)
{
    XLogRecPtr  current_recptr;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("WAL control functions cannot be executed during recovery.")));
 
    current_recptr = GetXLogWriteRecPtr();
 
    PG_RETURN_LSN(current_recptr);
}
 
/*
 * Report the current WAL insert location (same format as pg_backup_start etc)
 *
 * This function is mostly for debugging purposes.
 */
Datum
pg_current_wal_insert_lsn(PG_FUNCTION_ARGS)
{
    XLogRecPtr  current_recptr;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("WAL control functions cannot be executed during recovery.")));
 
    current_recptr = GetXLogInsertRecPtr();
 
    PG_RETURN_LSN(current_recptr);
}
 
/*
 * Report the current WAL flush location (same format as pg_backup_start etc)
 *
 * This function is mostly for debugging purposes.
 */
Datum
pg_current_wal_flush_lsn(PG_FUNCTION_ARGS)
{
    XLogRecPtr  current_recptr;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("WAL control functions cannot be executed during recovery.")));
 
    current_recptr = GetFlushRecPtr(NULL);
 
    PG_RETURN_LSN(current_recptr);
}
 
/*
 * Report the last WAL receive location (same format as pg_backup_start etc)
 *
 * This is useful for determining how much of WAL is guaranteed to be received
 * and synced to disk by walreceiver.
 */
Datum
pg_last_wal_receive_lsn(PG_FUNCTION_ARGS)
{
    XLogRecPtr  recptr;
 
    recptr = GetWalRcvFlushRecPtr(NULL, NULL);
 
    if (recptr == 0)
        PG_RETURN_NULL();
 
    PG_RETURN_LSN(recptr);
}
 
/*
 * Report the last WAL replay location (same format as pg_backup_start etc)
 *
 * This is useful for determining how much of WAL is visible to read-only
 * connections during recovery.
 */
Datum
pg_last_wal_replay_lsn(PG_FUNCTION_ARGS)
{
    XLogRecPtr  recptr;
 
    recptr = GetXLogReplayRecPtr(NULL);
 
    if (recptr == 0)
        PG_RETURN_NULL();
 
    PG_RETURN_LSN(recptr);
}
 
/*
 * Compute an xlog file name and decimal byte offset given a WAL location,
 * such as is returned by pg_backup_stop() or pg_switch_wal().
 */
Datum
pg_walfile_name_offset(PG_FUNCTION_ARGS)
{
    XLogSegNo   xlogsegno;
    uint32      xrecoff;
    XLogRecPtr  locationpoint = PG_GETARG_LSN(0);
    char        xlogfilename[MAXFNAMELEN];
    Datum       values[2];
    bool        isnull[2];
    TupleDesc   resultTupleDesc;
    HeapTuple   resultHeapTuple;
    Datum       result;
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("%s cannot be executed during recovery.",
                         "pg_walfile_name_offset()")));
 
    /*
     * Construct a tuple descriptor for the result row.  This must match this
     * function's pg_proc entry!
     */
    resultTupleDesc = CreateTemplateTupleDesc(2);
    TupleDescInitEntry(resultTupleDesc, (AttrNumber) 1, "file_name",
                       TEXTOID, -1, 0);
    TupleDescInitEntry(resultTupleDesc, (AttrNumber) 2, "file_offset",
                       INT4OID, -1, 0);
 
    resultTupleDesc = BlessTupleDesc(resultTupleDesc);
 
    /*
     * xlogfilename
     */
    XLByteToSeg(locationpoint, xlogsegno, wal_segment_size);
    XLogFileName(xlogfilename, GetWALInsertionTimeLine(), xlogsegno,
                 wal_segment_size);
 
    values[0] = CStringGetTextDatum(xlogfilename);
    isnull[0] = false;
 
    /*
     * offset
     */
    xrecoff = XLogSegmentOffset(locationpoint, wal_segment_size);
 
    values[1] = UInt32GetDatum(xrecoff);
    isnull[1] = false;
 
    /*
     * Tuple jam: Having first prepared your Datums, then squash together
     */
    resultHeapTuple = heap_form_tuple(resultTupleDesc, values, isnull);
 
    result = HeapTupleGetDatum(resultHeapTuple);
 
    PG_RETURN_DATUM(result);
}
 
/*
 * Compute an xlog file name given a WAL location,
 * such as is returned by pg_backup_stop() or pg_switch_wal().
 */
Datum
pg_walfile_name(PG_FUNCTION_ARGS)
{
    XLogSegNo   xlogsegno;
    XLogRecPtr  locationpoint = PG_GETARG_LSN(0);
    char        xlogfilename[MAXFNAMELEN];
 
    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
                 errhint("%s cannot be executed during recovery.",
                         "pg_walfile_name()")));
 
    XLByteToSeg(locationpoint, xlogsegno, wal_segment_size);
    XLogFileName(xlogfilename, GetWALInsertionTimeLine(), xlogsegno,
                 wal_segment_size);
 
    PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
}
 
/*
 * Extract the sequence number and the timeline ID from given a WAL file
 * name.
 */
Datum
pg_split_walfile_name(PG_FUNCTION_ARGS)
{
#define PG_SPLIT_WALFILE_NAME_COLS 2
    char       *fname = text_to_cstring(PG_GETARG_TEXT_PP(0));
    char       *fname_upper;
    char       *p;
    TimeLineID  tli;
    XLogSegNo   segno;
    Datum       values[PG_SPLIT_WALFILE_NAME_COLS] = {0};
    bool        isnull[PG_SPLIT_WALFILE_NAME_COLS] = {0};
    TupleDesc   tupdesc;
    HeapTuple   tuple;
    char        buf[256];
    Datum       result;
 
    fname_upper = pstrdup(fname);
 
    /* Capitalize WAL file name. */
    for (p = fname_upper; *p; p++)
        *p = pg_toupper((unsigned char) *p);
 
    if (!IsXLogFileName(fname_upper))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid WAL file name \"%s\"", fname)));
 
    XLogFromFileName(fname_upper, &tli, &segno, wal_segment_size);
 
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");
 
    /* Convert to numeric. */
    snprintf(buf, sizeof buf, UINT64_FORMAT, segno);
    values[0] = DirectFunctionCall3(numeric_in,
                                    CStringGetDatum(buf),
                                    ObjectIdGetDatum(0),
                                    Int32GetDatum(-1));
 
    values[1] = Int64GetDatum(tli);
 
    tuple = heap_form_tuple(tupdesc, values, isnull);
    result = HeapTupleGetDatum(tuple);
 
    PG_RETURN_DATUM(result);
 
#undef PG_SPLIT_WALFILE_NAME_COLS
}
 
/*
 * pg_wal_replay_pause - Request to pause recovery
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_wal_replay_pause(PG_FUNCTION_ARGS)
{
    if (!RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is not in progress"),
                 errhint("Recovery control functions can only be executed during recovery.")));
 
    if (PromoteIsTriggered())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("standby promotion is ongoing"),
                 errhint("%s cannot be executed after promotion is triggered.",
                         "pg_wal_replay_pause()")));
 
    SetRecoveryPause(true);
 
    /* wake up the recovery process so that it can process the pause request */
    WakeupRecovery();
 
    PG_RETURN_VOID();
}
 
/*
 * pg_wal_replay_resume - resume recovery now
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_wal_replay_resume(PG_FUNCTION_ARGS)
{
    if (!RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is not in progress"),
                 errhint("Recovery control functions can only be executed during recovery.")));
 
    if (PromoteIsTriggered())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("standby promotion is ongoing"),
                 errhint("%s cannot be executed after promotion is triggered.",
                         "pg_wal_replay_resume()")));
 
    SetRecoveryPause(false);
 
    PG_RETURN_VOID();
}
 
/*
 * pg_is_wal_replay_paused
 */
Datum
pg_is_wal_replay_paused(PG_FUNCTION_ARGS)
{
    if (!RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is not in progress"),
                 errhint("Recovery control functions can only be executed during recovery.")));
 
    PG_RETURN_BOOL(GetRecoveryPauseState() != RECOVERY_NOT_PAUSED);
}
 
/*
 * pg_get_wal_replay_pause_state - Returns the recovery pause state.
 *
 * Returned values:
 *
 * 'not paused' - if pause is not requested
 * 'pause requested' - if pause is requested but recovery is not yet paused
 * 'paused' - if recovery is paused
 */
Datum
pg_get_wal_replay_pause_state(PG_FUNCTION_ARGS)
{
    char       *statestr = NULL;
 
    if (!RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is not in progress"),
                 errhint("Recovery control functions can only be executed during recovery.")));
 
    /* get the recovery pause state */
    switch (GetRecoveryPauseState())
    {
        case RECOVERY_NOT_PAUSED:
            statestr = "not paused";
            break;
        case RECOVERY_PAUSE_REQUESTED:
            statestr = "pause requested";
            break;
        case RECOVERY_PAUSED:
            statestr = "paused";
            break;
    }
 
    Assert(statestr != NULL);
    PG_RETURN_TEXT_P(cstring_to_text(statestr));
}
 
/*
 * Returns timestamp of latest processed commit/abort record.
 *
 * When the server has been started normally without recovery the function
 * returns NULL.
 */
Datum
pg_last_xact_replay_timestamp(PG_FUNCTION_ARGS)
{
    TimestampTz xtime;
 
    xtime = GetLatestXTime();
    if (xtime == 0)
        PG_RETURN_NULL();
 
    PG_RETURN_TIMESTAMPTZ(xtime);
}
 
/*
 * Returns bool with current recovery mode, a global state.
 */
Datum
pg_is_in_recovery(PG_FUNCTION_ARGS)
{
    PG_RETURN_BOOL(RecoveryInProgress());
}
 
/*
 * Compute the difference in bytes between two WAL locations.
 */
Datum
pg_wal_lsn_diff(PG_FUNCTION_ARGS)
{
    Datum       result;
 
    result = DirectFunctionCall2(pg_lsn_mi,
                                 PG_GETARG_DATUM(0),
                                 PG_GETARG_DATUM(1));
 
    PG_RETURN_DATUM(result);
}
 
/*
 * Promotes a standby server.
 *
 * A result of "true" means that promotion has been completed if "wait" is
 * "true", or initiated if "wait" is false.
 */
Datum
pg_promote(PG_FUNCTION_ARGS)
{
    bool        wait = PG_GETARG_BOOL(0);
    int         wait_seconds = PG_GETARG_INT32(1);
    FILE       *promote_file;
    int         i;
 
    if (!RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is not in progress"),
                 errhint("Recovery control functions can only be executed during recovery.")));
 
    if (wait_seconds <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("\"wait_seconds\" must not be negative or zero")));
 
    /* create the promote signal file */
    promote_file = AllocateFile(PROMOTE_SIGNAL_FILE, "w");
    if (!promote_file)
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not create file \"%s\": %m",
                        PROMOTE_SIGNAL_FILE)));
 
    if (FreeFile(promote_file))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not write file \"%s\": %m",
                        PROMOTE_SIGNAL_FILE)));
 
    /* signal the postmaster */
    if (kill(PostmasterPid, SIGUSR1) != 0)
    {
        (void) unlink(PROMOTE_SIGNAL_FILE);
        ereport(ERROR,
                (errcode(ERRCODE_SYSTEM_ERROR),
                 errmsg("failed to send signal to postmaster: %m")));
    }
 
    /* return immediately if waiting was not requested */
    if (!wait)
        PG_RETURN_BOOL(true);
 
    /* wait for the amount of time wanted until promotion */
#define WAITS_PER_SECOND 10
    for (i = 0; i < WAITS_PER_SECOND * wait_seconds; i++)
    {
        int         rc;
 
        ResetLatch(MyLatch);
 
        if (!RecoveryInProgress())
            PG_RETURN_BOOL(true);
 
        CHECK_FOR_INTERRUPTS();
 
        rc = WaitLatch(MyLatch,
                       WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
                       1000L / WAITS_PER_SECOND,
                       WAIT_EVENT_PROMOTE);
 
        /*
         * Emergency bailout if postmaster has died.  This is to avoid the
         * necessity for manual cleanup of all postmaster children.
         */
        if (rc & WL_POSTMASTER_DEATH)
            ereport(FATAL,
                    (errcode(ERRCODE_ADMIN_SHUTDOWN),
                     errmsg("terminating connection due to unexpected postmaster exit"),
                     errcontext("while waiting on promotion")));
    }
 
    ereport(WARNING,
            (errmsg_plural("server did not promote within %d second",
                           "server did not promote within %d seconds",
                           wait_seconds,
                           wait_seconds)));
    PG_RETURN_BOOL(false);
}
 
/*
 * Waits until recovery replays the target LSN with optional timeout.
 */
Datum
pg_wal_replay_wait(PG_FUNCTION_ARGS)
{
    XLogRecPtr  target_lsn = PG_GETARG_LSN(0);
    int64       timeout = PG_GETARG_INT64(1);
 
    if (timeout < 0)
        ereport(ERROR,
                (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
                 errmsg("\"timeout\" must not be negative")));
 
    /*
     * We are going to wait for the LSN replay.  We should first care that we
     * don't hold a snapshot and correspondingly our MyProc->xmin is invalid.
     * Otherwise, our snapshot could prevent the replay of WAL records
     * implying a kind of self-deadlock.  This is the reason why
     * pg_wal_replay_wait() is a procedure, not a function.
     *
     * At first, we should check there is no active snapshot.  According to
     * PlannedStmtRequiresSnapshot(), even in an atomic context, CallStmt is
     * processed with a snapshot.  Thankfully, we can pop this snapshot,
     * because PortalRunUtility() can tolerate this.
     */
    if (ActiveSnapshotSet())
        PopActiveSnapshot();
 
    /*
     * At second, invalidate a catalog snapshot if any.  And we should be done
     * with the preparation.
     */
    InvalidateCatalogSnapshot();
 
    /* Give up if there is still an active or registered snapshot. */
    if (GetOldestSnapshot())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("pg_wal_replay_wait() must be only called without an active or registered snapshot"),
                 errdetail("Make sure pg_wal_replay_wait() isn't called within a transaction with an isolation level higher than READ COMMITTED, another procedure, or a function.")));
 
    /*
     * As the result we should hold no snapshot, and correspondingly our xmin
     * should be unset.
     */
    Assert(MyProc->xmin == InvalidTransactionId);
 
    (void) WaitForLSNReplay(target_lsn, timeout);
 
    PG_RETURN_VOID();
}