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) 1996-2019, 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.h"
#include "access/xlog_internal.h"
#include "access/xlogutils.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walreceiver.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/numeric.h"
#include "utils/guc.h"
#include "utils/pg_lsn.h"
#include "utils/timestamp.h"
#include "utils/tuplestore.h"
#include "storage/fd.h"
#include "storage/ipc.h"


/*
 * Store label file and tablespace map during non-exclusive backups.
 */
static StringInfo label_file;
static StringInfo tblspc_map_file;

/*
 * Called when the backend exits with a running non-exclusive base backup,
 * to clean up state.
 */
static void
nonexclusive_base_backup_cleanup(int code, Datum arg)
{
    do_pg_abort_backup();
    ereport(WARNING,
            (errmsg("aborting backup due to backend exiting before pg_stop_backup was called")));
}

/*
 * pg_start_backup: set up for taking an on-line backup dump
 *
 * Essentially what this does is to create a backup label file in $PGDATA,
 * where it will be archived as part of the backup dump.  The label file
 * contains the user-supplied label string (typically this would be used
 * to tell where the backup dump will be stored) and the starting time and
 * starting WAL location for the dump.
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_start_backup(PG_FUNCTION_ARGS)
{
    text       *backupid = PG_GETARG_TEXT_PP(0);
    bool        fast = PG_GETARG_BOOL(1);
    bool        exclusive = PG_GETARG_BOOL(2);
    char       *backupidstr;
    XLogRecPtr  startpoint;
    SessionBackupState status = get_backup_status();

    backupidstr = text_to_cstring(backupid);

    if (status == SESSION_BACKUP_NON_EXCLUSIVE)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("a backup is already in progress in this session")));

    if (exclusive)
    {
        startpoint = do_pg_start_backup(backupidstr, fast, NULL, NULL,
                                        NULL, NULL, false, true);
    }
    else
    {
        MemoryContext oldcontext;

        /*
         * Label file and tablespace map file need to be long-lived, since
         * they are read in pg_stop_backup.
         */
        oldcontext = MemoryContextSwitchTo(TopMemoryContext);
        label_file = makeStringInfo();
        tblspc_map_file = makeStringInfo();
        MemoryContextSwitchTo(oldcontext);

        startpoint = do_pg_start_backup(backupidstr, fast, NULL, label_file,
                                        NULL, tblspc_map_file, false, true);

        before_shmem_exit(nonexclusive_base_backup_cleanup, (Datum) 0);
    }

    PG_RETURN_LSN(startpoint);
}

/*
 * pg_stop_backup: finish taking an on-line backup dump
 *
 * We write an end-of-backup WAL record, and remove the backup label file
 * created by pg_start_backup, creating a backup history file in pg_wal
 * instead (whence it will immediately be archived). The backup history file
 * contains the same info found in the label file, plus the backup-end time
 * and WAL location. Before 9.0, the backup-end time was read from the backup
 * history file at the beginning of archive recovery, but we now use the WAL
 * record for that and the file is for informational and debug purposes only.
 *
 * Note: different from CancelBackup which just cancels online backup mode.
 *
 * Note: this version is only called to stop an exclusive backup. The function
 *       pg_stop_backup_v2 (overloaded as pg_stop_backup in SQL) is called to
 *       stop non-exclusive backups.
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_stop_backup(PG_FUNCTION_ARGS)
{
    XLogRecPtr  stoppoint;
    SessionBackupState status = get_backup_status();

    if (status == SESSION_BACKUP_NON_EXCLUSIVE)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("non-exclusive backup in progress"),
                 errhint("Did you mean to use pg_stop_backup('f')?")));

    /*
     * Exclusive backups were typically started in a different connection, so
     * don't try to verify that status of backup is set to
     * SESSION_BACKUP_EXCLUSIVE in this function. Actual verification that an
     * exclusive backup is in fact running is handled inside
     * do_pg_stop_backup.
     */
    stoppoint = do_pg_stop_backup(NULL, true, NULL);

    PG_RETURN_LSN(stoppoint);
}


/*
 * pg_stop_backup_v2: finish taking exclusive or nonexclusive on-line backup.
 *
 * Works the same as pg_stop_backup, except for non-exclusive backups it returns
 * the backup label and tablespace map files as text fields in as part of the
 * resultset.
 *
 * The first parameter (variable 'exclusive') allows the user to tell us if
 * this is an exclusive or a non-exclusive backup.
 *
 * The second 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.
 *
 * Permission checking for this function is managed through the normal
 * GRANT system.
 */
Datum
pg_stop_backup_v2(PG_FUNCTION_ARGS)
{
    ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
    TupleDesc   tupdesc;
    Tuplestorestate *tupstore;
    MemoryContext per_query_ctx;
    MemoryContext oldcontext;
    Datum       values[3];
    bool        nulls[3];

    bool        exclusive = PG_GETARG_BOOL(0);
    bool        waitforarchive = PG_GETARG_BOOL(1);
    XLogRecPtr  stoppoint;
    SessionBackupState status = get_backup_status();

    /* check to see if caller supports us returning a tuplestore */
    if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("set-valued function called in context that cannot accept a set")));
    if (!(rsinfo->allowedModes & SFRM_Materialize))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("materialize mode required, but it is not " \
                        "allowed in this context")));

    /* Build a tuple descriptor for our result type */
    if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
        elog(ERROR, "return type must be a row type");

    per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
    oldcontext = MemoryContextSwitchTo(per_query_ctx);

    tupstore = tuplestore_begin_heap(true, false, work_mem);
    rsinfo->returnMode = SFRM_Materialize;
    rsinfo->setResult = tupstore;
    rsinfo->setDesc = tupdesc;

    MemoryContextSwitchTo(oldcontext);

    MemSet(values, 0, sizeof(values));
    MemSet(nulls, 0, sizeof(nulls));

    if (exclusive)
    {
        if (status == SESSION_BACKUP_NON_EXCLUSIVE)
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("non-exclusive backup in progress"),
                     errhint("Did you mean to use pg_stop_backup('f')?")));

        /*
         * Stop the exclusive backup, and since we're in an exclusive backup
         * return NULL for both backup_label and tablespace_map.
         */
        stoppoint = do_pg_stop_backup(NULL, waitforarchive, NULL);

        nulls[1] = true;
        nulls[2] = true;
    }
    else
    {
        if (status != SESSION_BACKUP_NON_EXCLUSIVE)
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("non-exclusive backup is not in progress"),
                     errhint("Did you mean to use pg_stop_backup('t')?")));

        /*
         * Stop the non-exclusive backup. Return a copy of the backup label
         * and tablespace map so they can be written to disk by the caller.
         */
        stoppoint = do_pg_stop_backup(label_file->data, waitforarchive, NULL);
        cancel_before_shmem_exit(nonexclusive_base_backup_cleanup, (Datum) 0);

        values[1] = CStringGetTextDatum(label_file->data);
        values[2] = CStringGetTextDatum(tblspc_map_file->data);

        /* Free structures allocated in TopMemoryContext */
        pfree(label_file->data);
        pfree(label_file);
        label_file = NULL;
        pfree(tblspc_map_file->data);
        pfree(tblspc_map_file);
        tblspc_map_file = NULL;
    }

    /* Stoppoint is included on both exclusive and nonexclusive backups */
    values[0] = LSNGetDatum(stoppoint);

    tuplestore_putvalues(tupstore, tupdesc, values, nulls);
    tuplestore_donestoring(tupstore);

    return (Datum) 0;
}

/*
 * 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_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_start_backup 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_start_backup 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_start_backup 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();

    PG_RETURN_LSN(current_recptr);
}

/*
 * Report the last WAL receive location (same format as pg_start_backup 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 = GetWalRcvWriteRecPtr(NULL, NULL);

    if (recptr == 0)
        PG_RETURN_NULL();

    PG_RETURN_LSN(recptr);
}

/*
 * Report the last WAL replay location (same format as pg_start_backup 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_stop_backup() or pg_switch_wal().
 *
 * Note that a location exactly at a segment boundary is taken to be in
 * the previous segment.  This is usually the right thing, since the
 * expected usage is to determine which xlog file(s) are ready to archive.
 */
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
     */
    XLByteToPrevSeg(locationpoint, xlogsegno, wal_segment_size);
    XLogFileName(xlogfilename, ThisTimeLineID, 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_stop_backup() 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()")));

    XLByteToPrevSeg(locationpoint, xlogsegno, wal_segment_size);
    XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno, wal_segment_size);

    PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
}

/*
 * pg_wal_replay_pause - pause recovery now
 *
 * 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.")));

    SetRecoveryPause(true);

    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.")));

    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(RecoveryIsPaused());
}

/*
 * 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_NUMERIC(result);
}

/*
 * Returns bool with current on-line backup mode, a global state.
 */
Datum
pg_is_in_backup(PG_FUNCTION_ARGS)
{
    PG_RETURN_BOOL(BackupInProgress());
}

/*
 * Returns start time of an online exclusive backup.
 *
 * When there's no exclusive backup in progress, the function
 * returns NULL.
 */
Datum
pg_backup_start_time(PG_FUNCTION_ARGS)
{
    Datum       xtime;
    FILE       *lfp;
    char        fline[MAXPGPATH];
    char        backup_start_time[30];

    /*
     * See if label file is present
     */
    lfp = AllocateFile(BACKUP_LABEL_FILE, "r");
    if (lfp == NULL)
    {
        if (errno != ENOENT)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not read file \"%s\": %m",
                            BACKUP_LABEL_FILE)));
        PG_RETURN_NULL();
    }

    /*
     * Parse the file to find the START TIME line.
     */
    backup_start_time[0] = '\0';
    while (fgets(fline, sizeof(fline), lfp) != NULL)
    {
        if (sscanf(fline, "START TIME: %25[^\n]\n", backup_start_time) == 1)
            break;
    }

    /* Check for a read error. */
    if (ferror(lfp))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not read file \"%s\": %m", BACKUP_LABEL_FILE)));

    /* Close the backup label file. */
    if (FreeFile(lfp))
        ereport(ERROR,
                (errcode_for_file_access(),
                 errmsg("could not close file \"%s\": %m", BACKUP_LABEL_FILE)));

    if (strlen(backup_start_time) == 0)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));

    /*
     * Convert the time string read from file to TimestampTz form.
     */
    xtime = DirectFunctionCall3(timestamptz_in,
                                CStringGetDatum(backup_start_time),
                                ObjectIdGetDatum(InvalidOid),
                                Int32GetDatum(-1));

    PG_RETURN_DATUM(xtime);
}

/*
 * 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\" cannot be negative or equal 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)
    {
        ereport(WARNING,
                (errmsg("failed to send signal to postmaster: %m")));
        (void) unlink(PROMOTE_SIGNAL_FILE);
        PG_RETURN_BOOL(false);
    }

    /* 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++)
    {
        ResetLatch(MyLatch);

        if (!RecoveryInProgress())
            PG_RETURN_BOOL(true);

        CHECK_FOR_INTERRUPTS();

        (void) WaitLatch(MyLatch,
                         WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
                         1000L / WAITS_PER_SECOND,
                         WAIT_EVENT_PROMOTE);
    }

    ereport(WARNING,
            (errmsg("server did not promote within %d seconds", wait_seconds)));
    PG_RETURN_BOOL(false);
}