text: /*-------------------------------------------------------------------------
   *
   * xlogfuncs.c
   *
   * PostgreSQL write-ahead log manager user interface functions
   *
   * This file contains WAL control and information functions.
   *
   *
   * Portions Copyright (c) 1996-2018, 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_internal.h"
  #include "access/xlogutils.h"
  #include "catalog/catalog.h"
  #include "catalog/pg_type.h"
  #include "funcapi.h"
  #include "miscadmin.h"
  #include "postmaster/checksumhelper.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(typstore);
  
  	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("pg_walfile_name_offset() cannot be executed during recovery.")));
  
  	/*
  	 * 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, 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("pg_walfile_name() cannot be executed during recovery.")));
  
  	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);
  }
  
  /*
   * Disables checksums for the cluster, unless already disabled.
   *
   * Has immediate effect - the checksums are set to off right away.
   */
  Datum
  disable_data_checksums(PG_FUNCTION_ARGS)
  {
  	/*
  	 * If we don't need to write new checksums, then clearly they are already
  	 * disabled.
  	 */
  	if (!DataChecksumsNeedWrite())
  		ereport(ERROR,
  				(errmsg("data checksums already disabled")));
  
  	ShutdownChecksumHelperIfRunning();
  
  	SetDataChecksumsOff();
  
  	PG_RETURN_VOID();
  }
  
  /*
   * Enables checksums for the cluster, unless already enabled.
   *
   * Supports vacuum-like cost-based throttling, to limit system load.
   * Starts a background worker that updates checksums on existing data.
   */
  Datum
  enable_data_checksums(PG_FUNCTION_ARGS)
  {
  	int			cost_delay = PG_GETARG_INT32(0);
  	int			cost_limit = PG_GETARG_INT32(1);
  
  	if (cost_delay < 0)
  		ereport(ERROR,
  				(errmsg("cost delay cannot be less than zero")));
  	if (cost_limit <= 0)
  		ereport(ERROR,
  				(errmsg("cost limit must be a positive value")));
  
  	/*
  	 * Allow state change from "off" or from "inprogress", since this is how
  	 * we restart the worker if necessary.
  	 */
  	if (DataChecksumsNeedVerify())
  		ereport(ERROR,
  				(errmsg("data checksums already enabled")));
  
  	SetDataChecksumsInProgress();
  	if (!StartChecksumHelperLauncher(cost_delay, cost_limit))
  		ereport(ERROR,
  				(errmsg("failed to start checksum helper process")));
  
  	PG_RETURN_VOID();
  }
  