Add functions pg_start_backup, pg_stop_backup to create backup label

and history files as per recent discussion.  While at it, remove
pg_terminate_backend, since we have decided we do not have time during
this release cycle to address the reliability concerns it creates.
Split the 'Miscellaneous Functions' documentation section into
'System Information Functions' and 'System Administration Functions',
which hopefully will draw the eyes of those looking for such things.

1 files changed, 231 insertions, 1 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b0fac745266..59666580035 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.153 2004/08/01 17:45:42 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.154 2004/08/03 20:32:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -5048,3 +5048,233 @@ issue_xlog_fsync(void)
 			break;
 	}
 }
+
+
+/*
+ * 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 offset for the dump.
+ */
+Datum
+pg_start_backup(PG_FUNCTION_ARGS)
+{
+	text	   *backupid = PG_GETARG_TEXT_P(0);
+	text	   *result;
+	char	   *backupidstr;
+	XLogRecPtr	startpoint;
+	time_t stamp_time;
+	char		strfbuf[128];
+	char		labelfilename[MAXPGPATH];
+	char		xlogfilename[MAXFNAMELEN];
+	uint32		_logId;
+	uint32		_logSeg;
+	struct stat stat_buf;
+	FILE	   *fp;
+
+	if (!superuser()) 
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 (errmsg("must be superuser to run a backup"))));
+	backupidstr = DatumGetCString(DirectFunctionCall1(textout,
+													  PointerGetDatum(backupid)));
+	/*
+	 * The oldest point in WAL that would be needed to restore starting from
+	 * the most recent checkpoint is precisely the RedoRecPtr.
+	 */
+	startpoint = GetRedoRecPtr();
+	XLByteToSeg(startpoint, _logId, _logSeg);
+	XLogFileName(xlogfilename, ThisTimeLineID, _logId, _logSeg);
+	/*
+	 * We deliberately use strftime/localtime not the src/timezone functions,
+	 * so that backup labels will consistently be recorded in the same
+	 * timezone regardless of TimeZone setting.  This matches elog.c's
+	 * practice.
+	 */
+	stamp_time = time(NULL);
+	strftime(strfbuf, sizeof(strfbuf),
+			 "%Y-%m-%d %H:%M:%S %Z",
+			 localtime(&stamp_time));
+	/*
+	 * Check for existing backup label --- implies a backup is already running
+	 */
+	snprintf(labelfilename, MAXPGPATH, "%s/backup_label", DataDir);
+	if (stat(labelfilename, &stat_buf) != 0)
+	{
+		if (errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not stat \"%s\": %m",
+							labelfilename)));
+	}
+	else
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("a backup is already in progress"),
+				 errhint("If you're sure there is no backup in progress, remove file \"%s\" and try again.",
+						 labelfilename)));
+	/*
+	 * Okay, write the file
+	 */
+	fp = AllocateFile(labelfilename, "w");
+	if (!fp)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+						labelfilename)));
+	fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
+			startpoint.xlogid, startpoint.xrecoff, xlogfilename);
+	fprintf(fp, "START TIME: %s\n", strfbuf);
+	fprintf(fp, "LABEL: %s\n", backupidstr);
+	if (fflush(fp) || ferror(fp) || FreeFile(fp))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write file \"%s\": %m",
+						labelfilename)));
+	/*
+	 * We're done.  As a convenience, return the starting WAL offset.
+	 */
+	snprintf(xlogfilename, sizeof(xlogfilename), "%X/%X",
+			 startpoint.xlogid, startpoint.xrecoff);
+	result = DatumGetTextP(DirectFunctionCall1(textin,
+											   CStringGetDatum(xlogfilename)));
+	PG_RETURN_TEXT_P(result);
+}
+
+/*
+ * pg_stop_backup: finish taking an on-line backup dump
+ *
+ * We remove the backup label file created by pg_start_backup, and instead
+ * create a backup history file in pg_xlog (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 offset.
+ */
+Datum
+pg_stop_backup(PG_FUNCTION_ARGS)
+{
+	text	   *result;
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	XLogRecPtr	startpoint;
+	XLogRecPtr	stoppoint;
+	time_t stamp_time;
+	char		strfbuf[128];
+	char		labelfilename[MAXPGPATH];
+	char		histfilename[MAXPGPATH];
+	char		startxlogfilename[MAXFNAMELEN];
+	char		stopxlogfilename[MAXFNAMELEN];
+	uint32		_logId;
+	uint32		_logSeg;
+	FILE	   *lfp;
+	FILE	   *fp;
+	char		ch;
+	int			ich;
+
+	if (!superuser()) 
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 (errmsg("must be superuser to run a backup"))));
+	/*
+	 * Get the current end-of-WAL position; it will be unsafe to use this
+	 * dump to restore to a point in advance of this time.
+	 */
+	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
+	INSERT_RECPTR(stoppoint, Insert, Insert->curridx);
+	LWLockRelease(WALInsertLock);
+
+	XLByteToSeg(stoppoint, _logId, _logSeg);
+	XLogFileName(stopxlogfilename, ThisTimeLineID, _logId, _logSeg);
+	/*
+	 * We deliberately use strftime/localtime not the src/timezone functions,
+	 * so that backup labels will consistently be recorded in the same
+	 * timezone regardless of TimeZone setting.  This matches elog.c's
+	 * practice.
+	 */
+	stamp_time = time(NULL);
+	strftime(strfbuf, sizeof(strfbuf),
+			 "%Y-%m-%d %H:%M:%S %Z",
+			 localtime(&stamp_time));
+	/*
+	 * Open the existing label file
+	 */
+	snprintf(labelfilename, MAXPGPATH, "%s/backup_label", DataDir);
+	lfp = AllocateFile(labelfilename, "r");
+	if (!lfp)
+	{
+		if (errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							labelfilename)));
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("a backup is not in progress")));
+	}
+	/*
+	 * Read and parse the START WAL LOCATION line (this code is pretty
+	 * crude, but we are not expecting any variability in the file format).
+	 */
+	if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %24s)%c",
+			   &startpoint.xlogid, &startpoint.xrecoff, startxlogfilename,
+			   &ch) != 4 || ch != '\n')
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("invalid data in file \"%s\"", labelfilename)));
+	/*
+	 * Write the backup history file
+	 */
+	XLByteToSeg(startpoint, _logId, _logSeg);
+	BackupHistoryFilePath(histfilename, ThisTimeLineID, _logId, _logSeg,
+						  startpoint.xrecoff % XLogSegSize);
+	fp = AllocateFile(histfilename, "w");
+	if (!fp)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+						histfilename)));
+	fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
+			startpoint.xlogid, startpoint.xrecoff, startxlogfilename);
+	fprintf(fp, "STOP WAL LOCATION: %X/%X (file %s)\n",
+			stoppoint.xlogid, stoppoint.xrecoff, stopxlogfilename);
+	/* transfer start time and label lines from label to history file */
+	while ((ich = fgetc(lfp)) != EOF)
+		fputc(ich, fp);
+	fprintf(fp, "STOP TIME: %s\n", strfbuf);
+	if (fflush(fp) || ferror(fp) || FreeFile(fp))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write file \"%s\": %m",
+						histfilename)));
+	/*
+	 * Close and remove the backup label file
+	 */
+	if (ferror(lfp) || FreeFile(lfp))
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not read file \"%s\": %m",
+						labelfilename)));
+	if (unlink(labelfilename) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not remove file \"%s\": %m",
+						labelfilename)));
+	/*
+	 * Notify archiver that history file may be archived immediately
+	 */
+	if (XLogArchivingActive())
+	{
+		BackupHistoryFileName(histfilename, ThisTimeLineID, _logId, _logSeg,
+							  startpoint.xrecoff % XLogSegSize);
+		XLogArchiveNotify(histfilename);
+	}
+	/*
+	 * We're done.  As a convenience, return the ending WAL offset.
+	 */
+	snprintf(stopxlogfilename, sizeof(stopxlogfilename), "%X/%X",
+			 stoppoint.xlogid, stoppoint.xrecoff);
+	result = DatumGetTextP(DirectFunctionCall1(textin,
+											   CStringGetDatum(stopxlogfilename)));
+	PG_RETURN_TEXT_P(result);
+}