xlogfuncs.c

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/*-------------------------------------------------------------------------
 *
 * xlogfuncs.c
 *
 * PostgreSQL transaction log manager user interface functions
 *
 * This file contains WAL control and information functions.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/access/transam/xlogfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/xlog.h"
#include "access/xlog_fn.h"
#include "access/xlog_internal.h"
#include "access/xlogutils.h"
#include "catalog/catalog.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "replication/walreceiver.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/numeric.h"
#include "utils/guc.h"
#include "utils/timestamp.h"
#include "storage/fd.h"

static void validate_xlog_location(char *str);


/*
 * 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.
 */
Datum
pg_start_backup(PG_FUNCTION_ARGS)
{
    text       *backupid = PG_GETARG_TEXT_P(0);
    bool        fast = PG_GETARG_BOOL(1);
    char       *backupidstr;
    XLogRecPtr  startpoint;
    char        startxlogstr[MAXFNAMELEN];

    backupidstr = text_to_cstring(backupid);

    startpoint = do_pg_start_backup(backupidstr, fast, NULL, NULL);

    snprintf(startxlogstr, sizeof(startxlogstr), "%X/%X",
             (uint32) (startpoint >> 32), (uint32) startpoint);
    PG_RETURN_TEXT_P(cstring_to_text(startxlogstr));
}

/*
 * 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_xlog
 * 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.
 */
Datum
pg_stop_backup(PG_FUNCTION_ARGS)
{
    XLogRecPtr  stoppoint;
    char        stopxlogstr[MAXFNAMELEN];

    stoppoint = do_pg_stop_backup(NULL, true, NULL);

    snprintf(stopxlogstr, sizeof(stopxlogstr), "%X/%X",
             (uint32) (stoppoint >> 32), (uint32) stoppoint);
    PG_RETURN_TEXT_P(cstring_to_text(stopxlogstr));
}

/*
 * pg_switch_xlog: switch to next xlog file
 */
Datum
pg_switch_xlog(PG_FUNCTION_ARGS)
{
    XLogRecPtr  switchpoint;
    char        location[MAXFNAMELEN];

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
             (errmsg("must be superuser to switch transaction log files"))));

    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();

    /*
     * As a convenience, return the WAL location of the switch record
     */
    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (switchpoint >> 32), (uint32) switchpoint);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * pg_create_restore_point: a named point for restore
 */
Datum
pg_create_restore_point(PG_FUNCTION_ARGS)
{
    text       *restore_name = PG_GETARG_TEXT_P(0);
    char       *restore_name_str;
    XLogRecPtr  restorepoint;
    char        location[MAXFNAMELEN];

    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to create a restore point"))));

    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 \"archive\" or \"hot_standby\" 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
     */
    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (restorepoint >> 32), (uint32) restorepoint);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * 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_xlog_location(PG_FUNCTION_ARGS)
{
    XLogRecPtr  current_recptr;
    char        location[MAXFNAMELEN];

    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();

    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (current_recptr >> 32), (uint32) current_recptr);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * Report the current WAL insert location (same format as pg_start_backup etc)
 *
 * This function is mostly for debugging purposes.
 */
Datum
pg_current_xlog_insert_location(PG_FUNCTION_ARGS)
{
    XLogRecPtr  current_recptr;
    char        location[MAXFNAMELEN];

    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();

    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (current_recptr >> 32), (uint32) current_recptr);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * 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_xlog_receive_location(PG_FUNCTION_ARGS)
{
    XLogRecPtr  recptr;
    char        location[MAXFNAMELEN];

    recptr = GetWalRcvWriteRecPtr(NULL, NULL);

    if (recptr == 0)
        PG_RETURN_NULL();

    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (recptr >> 32), (uint32) recptr);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * 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_xlog_replay_location(PG_FUNCTION_ARGS)
{
    XLogRecPtr  recptr;
    char        location[MAXFNAMELEN];

    recptr = GetXLogReplayRecPtr(NULL);

    if (recptr == 0)
        PG_RETURN_NULL();

    snprintf(location, sizeof(location), "%X/%X",
             (uint32) (recptr >> 32), (uint32) recptr);
    PG_RETURN_TEXT_P(cstring_to_text(location));
}

/*
 * Compute an xlog file name and decimal byte offset given a WAL location,
 * such as is returned by pg_stop_backup() or pg_xlog_switch().
 *
 * 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_xlogfile_name_offset(PG_FUNCTION_ARGS)
{
    text       *location = PG_GETARG_TEXT_P(0);
    char       *locationstr;
    uint32      hi,
                lo;
    XLogSegNo   xlogsegno;
    uint32      xrecoff;
    XLogRecPtr  locationpoint;
    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("pg_xlogfile_name_offset() cannot be executed during recovery.")));

    /*
     * Read input and parse
     */
    locationstr = text_to_cstring(location);

    validate_xlog_location(locationstr);

    if (sscanf(locationstr, "%X/%X", &hi, &lo) != 2)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not parse transaction log location \"%s\"",
                        locationstr)));
    locationpoint = ((uint64) hi) << 32 | lo;

    /*
     * Construct a tuple descriptor for the result row.  This must match this
     * function's pg_proc entry!
     */
    resultTupleDesc = CreateTemplateTupleDesc(2, false);
    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);
    XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno);

    values[0] = CStringGetTextDatum(xlogfilename);
    isnull[0] = false;

    /*
     * offset
     */
    xrecoff = locationpoint % XLogSegSize;

    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_xlog_switch().
 */
Datum
pg_xlogfile_name(PG_FUNCTION_ARGS)
{
    text       *location = PG_GETARG_TEXT_P(0);
    char       *locationstr;
    uint32      hi,
                lo;
    XLogSegNo   xlogsegno;
    XLogRecPtr  locationpoint;
    char        xlogfilename[MAXFNAMELEN];

    if (RecoveryInProgress())
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("recovery is in progress"),
         errhint("pg_xlogfile_name() cannot be executed during recovery.")));

    locationstr = text_to_cstring(location);

    validate_xlog_location(locationstr);

    if (sscanf(locationstr, "%X/%X", &hi, &lo) != 2)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("could not parse transaction log location \"%s\"",
                        locationstr)));
    locationpoint = ((uint64) hi) << 32 | lo;

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

    PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
}

/*
 * pg_xlog_replay_pause - pause recovery now
 */
Datum
pg_xlog_replay_pause(PG_FUNCTION_ARGS)
{
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to control recovery"))));

    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_xlog_replay_resume - resume recovery now
 */
Datum
pg_xlog_replay_resume(PG_FUNCTION_ARGS)
{
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to control recovery"))));

    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_xlog_replay_paused
 */
Datum
pg_is_xlog_replay_paused(PG_FUNCTION_ARGS)
{
    if (!superuser())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 (errmsg("must be superuser to control recovery"))));

    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());
}

/*
 * Validate the text form of a transaction log location.
 * (Just using sscanf() input allows incorrect values such as
 * negatives, so we have to be a bit more careful about that).
 */
static void
validate_xlog_location(char *str)
{
#define MAXLSNCOMPONENT     8

    int         len1,
                len2;

    len1 = strspn(str, "0123456789abcdefABCDEF");
    if (len1 < 1 || len1 > MAXLSNCOMPONENT || str[len1] != '/')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for transaction log location: \"%s\"", str)));

    len2 = strspn(str + len1 + 1, "0123456789abcdefABCDEF");
    if (len2 < 1 || len2 > MAXLSNCOMPONENT || str[len1 + 1 + len2] != '\0')
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
                 errmsg("invalid input syntax for transaction log location: \"%s\"", str)));
}

/*
 * Compute the difference in bytes between two WAL locations.
 */
Datum
pg_xlog_location_diff(PG_FUNCTION_ARGS)
{
    text       *location1 = PG_GETARG_TEXT_P(0);
    text       *location2 = PG_GETARG_TEXT_P(1);
    char       *str1,
               *str2;
    XLogRecPtr  loc1,
                loc2;
    Numeric     result;
    uint64      bytes1,
                bytes2;
    uint32      hi,
                lo;

    /*
     * Read and parse input
     */
    str1 = text_to_cstring(location1);
    str2 = text_to_cstring(location2);

    validate_xlog_location(str1);
    validate_xlog_location(str2);

    if (sscanf(str1, "%X/%X", &hi, &lo) != 2)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
           errmsg("could not parse transaction log location \"%s\"", str1)));
    loc1 = ((uint64) hi) << 32 | lo;

    if (sscanf(str2, "%X/%X", &hi, &lo) != 2)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
           errmsg("could not parse transaction log location \"%s\"", str2)));
    loc2 = ((uint64) hi) << 32 | lo;

    bytes1 = (uint64) loc1;
    bytes2 = (uint64) loc2;

    /*
     * result = bytes1 - bytes2.
     *
     * XXX: this won't handle values higher than 2^63 correctly.
     */
    result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
       DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) bytes1)),
       DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) bytes2))));

    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 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);
}