xlog.c

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

 *
 * use_lock: if TRUE, acquire ControlFileLock while moving file into
 * place.  This should be TRUE except during bootstrap log creation.  The
 * caller must *not* hold the lock at call.
 *
 * Returns FD of opened file.
 *
 * Note: errors here are ERROR not PANIC because we might or might not be
 * inside a critical section (eg, during checkpoint there is no reason to
 * take down the system on failure).  They will promote to PANIC if we are
 * in a critical section.
 */
static int
XLogFileInit(uint32 log, uint32 seg,
			 bool *use_existent, bool use_lock)
{
	char		path[MAXPGPATH];
	char		tmppath[MAXPGPATH];
	char		zbuffer[BLCKSZ];
	uint32		installed_log;
	uint32		installed_seg;
	int			max_advance;
	int			fd;
	int			nbytes;

	XLogFilePath(path, ThisTimeLineID, log, seg);

	/*
	 * Try to use existent file (checkpoint maker may have created it already)
	 */
	if (*use_existent)
	{
		fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
						   S_IRUSR | S_IWUSR);
		if (fd < 0)
		{
			if (errno != ENOENT)
				ereport(ERROR,
						(errcode_for_file_access(),
						 errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
								path, log, seg)));
		}
		else
			return (fd);
	}

	/*
	 * Initialize an empty (all zeroes) segment.  NOTE: it is possible that
	 * another process is doing the same thing.  If so, we will end up
	 * pre-creating an extra log segment.  That seems OK, and better than
	 * holding the lock throughout this lengthy process.
	 */
	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());

	unlink(tmppath);

	/* do not use XLOG_SYNC_BIT here --- want to fsync only at end of fill */
	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
					   S_IRUSR | S_IWUSR);
	if (fd < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not create file \"%s\": %m", tmppath)));

	/*
	 * Zero-fill the file.	We have to do this the hard way to ensure that all
	 * the file space has really been allocated --- on platforms that allow
	 * "holes" in files, just seeking to the end doesn't allocate intermediate
	 * space.  This way, we know that we have all the space and (after the
	 * fsync below) that all the indirect blocks are down on disk.	Therefore,
	 * fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
	 * log file.
	 */
	MemSet(zbuffer, 0, sizeof(zbuffer));
	for (nbytes = 0; nbytes < XLogSegSize; nbytes += sizeof(zbuffer))
	{
		errno = 0;
		if ((int) write(fd, zbuffer, sizeof(zbuffer)) != (int) sizeof(zbuffer))
		{
			int			save_errno = errno;

			/*
			 * If we fail to make the file, delete it to release disk space
			 */
			unlink(tmppath);
			/* if write didn't set errno, assume problem is no disk space */
			errno = save_errno ? save_errno : ENOSPC;

			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not write to file \"%s\": %m", tmppath)));
		}
	}

	if (pg_fsync(fd) != 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not fsync file \"%s\": %m", tmppath)));

	if (close(fd))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not close file \"%s\": %m", tmppath)));

	/*
	 * Now move the segment into place with its final name.
	 *
	 * If caller didn't want to use a pre-existing file, get rid of any
	 * pre-existing file.  Otherwise, cope with possibility that someone else
	 * has created the file while we were filling ours: if so, use ours to
	 * pre-create a future log segment.
	 */
	installed_log = log;
	installed_seg = seg;
	max_advance = XLOGfileslop;
	if (!InstallXLogFileSegment(&installed_log, &installed_seg, tmppath,
								*use_existent, &max_advance,
								use_lock))
	{
		/* No need for any more future segments... */
		unlink(tmppath);
	}

	/* Set flag to tell caller there was no existent file */
	*use_existent = false;

	/* Now open original target segment (might not be file I just made) */
	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
					   S_IRUSR | S_IWUSR);
	if (fd < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
				  path, log, seg)));

	return (fd);
}

/*
 * Create a new XLOG file segment by copying a pre-existing one.
 *
 * log, seg: identify segment to be created.
 *
 * srcTLI, srclog, srcseg: identify segment to be copied (could be from
 *		a different timeline)
 *
 * Currently this is only used during recovery, and so there are no locking
 * considerations.	But we should be just as tense as XLogFileInit to avoid
 * emplacing a bogus file.
 */
static void
XLogFileCopy(uint32 log, uint32 seg,
			 TimeLineID srcTLI, uint32 srclog, uint32 srcseg)
{
	char		path[MAXPGPATH];
	char		tmppath[MAXPGPATH];
	char		buffer[BLCKSZ];
	int			srcfd;
	int			fd;
	int			nbytes;

	/*
	 * Open the source file
	 */
	XLogFilePath(path, srcTLI, srclog, srcseg);
	srcfd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
	if (srcfd < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not open file \"%s\": %m", path)));

	/*
	 * Copy into a temp file name.
	 */
	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());

	unlink(tmppath);

	/* do not use XLOG_SYNC_BIT here --- want to fsync only at end of fill */
	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
					   S_IRUSR | S_IWUSR);
	if (fd < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not create file \"%s\": %m", tmppath)));

	/*
	 * Do the data copying.
	 */
	for (nbytes = 0; nbytes < XLogSegSize; nbytes += sizeof(buffer))
	{
		errno = 0;
		if ((int) read(srcfd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
		{
			if (errno != 0)
				ereport(ERROR,
						(errcode_for_file_access(),
						 errmsg("could not read file \"%s\": %m", path)));
			else
				ereport(ERROR,
						(errmsg("not enough data in file \"%s\"", path)));
		}
		errno = 0;
		if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
		{
			int			save_errno = errno;

			/*
			 * If we fail to make the file, delete it to release disk space
			 */
			unlink(tmppath);
			/* if write didn't set errno, assume problem is no disk space */
			errno = save_errno ? save_errno : ENOSPC;

			ereport(ERROR,
					(errcode_for_file_access(),
					 errmsg("could not write to file \"%s\": %m", tmppath)));
		}
	}

	if (pg_fsync(fd) != 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not fsync file \"%s\": %m", tmppath)));

	if (close(fd))
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not close file \"%s\": %m", tmppath)));

	close(srcfd);

	/*
	 * Now move the segment into place with its final name.
	 */
	if (!InstallXLogFileSegment(&log, &seg, tmppath, false, NULL, false))
		elog(ERROR, "InstallXLogFileSegment should not have failed");
}

/*
 * Install a new XLOG segment file as a current or future log segment.
 *
 * This is used both to install a newly-created segment (which has a temp
 * filename while it's being created) and to recycle an old segment.
 *
 * *log, *seg: identify segment to install as (or first possible target).
 * When find_free is TRUE, these are modified on return to indicate the
 * actual installation location or last segment searched.
 *
 * tmppath: initial name of file to install.  It will be renamed into place.
 *
 * find_free: if TRUE, install the new segment at the first empty log/seg
 * number at or after the passed numbers.  If FALSE, install the new segment
 * exactly where specified, deleting any existing segment file there.
 *
 * *max_advance: maximum number of log/seg slots to advance past the starting
 * point.  Fail if no free slot is found in this range.  On return, reduced
 * by the number of slots skipped over.  (Irrelevant, and may be NULL,
 * when find_free is FALSE.)
 *
 * use_lock: if TRUE, acquire ControlFileLock while moving file into
 * place.  This should be TRUE except during bootstrap log creation.  The
 * caller must *not* hold the lock at call.
 *
 * Returns TRUE if file installed, FALSE if not installed because of
 * exceeding max_advance limit.  (Any other kind of failure causes ereport().)
 */
static bool
InstallXLogFileSegment(uint32 *log, uint32 *seg, char *tmppath,
					   bool find_free, int *max_advance,
					   bool use_lock)
{
	char		path[MAXPGPATH];
	struct stat stat_buf;

	XLogFilePath(path, ThisTimeLineID, *log, *seg);

	/*
	 * We want to be sure that only one process does this at a time.
	 */
	if (use_lock)
		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);

	if (!find_free)
	{
		/* Force installation: get rid of any pre-existing segment file */
		unlink(path);
	}
	else
	{
		/* Find a free slot to put it in */
		while (stat(path, &stat_buf) == 0)
		{
			if (*max_advance <= 0)
			{
				/* Failed to find a free slot within specified range */
				if (use_lock)
					LWLockRelease(ControlFileLock);
				return false;
			}
			NextLogSeg(*log, *seg);
			(*max_advance)--;
			XLogFilePath(path, ThisTimeLineID, *log, *seg);
		}
	}

	/*
	 * Prefer link() to rename() here just to be really sure that we don't
	 * overwrite an existing logfile.  However, there shouldn't be one, so
	 * rename() is an acceptable substitute except for the truly paranoid.
	 */
#if HAVE_WORKING_LINK
	if (link(tmppath, path) < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not link file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
						tmppath, path, *log, *seg)));
	unlink(tmppath);
#else
	if (rename(tmppath, path) < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not rename file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
						tmppath, path, *log, *seg)));
#endif

	if (use_lock)
		LWLockRelease(ControlFileLock);

	return true;
}

/*
 * Open a pre-existing logfile segment for writing.
 */
static int
XLogFileOpen(uint32 log, uint32 seg)
{
	char		path[MAXPGPATH];
	int			fd;

	XLogFilePath(path, ThisTimeLineID, log, seg);

	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | XLOG_SYNC_BIT,
					   S_IRUSR | S_IWUSR);
	if (fd < 0)
		ereport(PANIC,
				(errcode_for_file_access(),
		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
				  path, log, seg)));

	return fd;
}

/*
 * Open a logfile segment for reading (during recovery).
 */
static int
XLogFileRead(uint32 log, uint32 seg, int emode)
{
	char		path[MAXPGPATH];
	char		xlogfname[MAXFNAMELEN];
	ListCell   *cell;
	int			fd;

	/*
	 * Loop looking for a suitable timeline ID: we might need to read any of
	 * the timelines listed in expectedTLIs.
	 *
	 * We expect curFileTLI on entry to be the TLI of the preceding file in
	 * sequence, or 0 if there was no predecessor.	We do not allow curFileTLI
	 * to go backwards; this prevents us from picking up the wrong file when a
	 * parent timeline extends to higher segment numbers than the child we
	 * want to read.
	 */
	foreach(cell, expectedTLIs)
	{
		TimeLineID	tli = (TimeLineID) lfirst_int(cell);

		if (tli < curFileTLI)
			break;				/* don't bother looking at too-old TLIs */

		if (InArchiveRecovery)
		{
			XLogFileName(xlogfname, tli, log, seg);
			restoredFromArchive = RestoreArchivedFile(path, xlogfname,
													  "RECOVERYXLOG",
													  XLogSegSize);
		}
		else
			XLogFilePath(path, tli, log, seg);

		fd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
		if (fd >= 0)
		{
			/* Success! */
			curFileTLI = tli;
			return fd;
		}
		if (errno != ENOENT)	/* unexpected failure? */
			ereport(PANIC,
					(errcode_for_file_access(),
			errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
				   path, log, seg)));
	}

	/* Couldn't find it.  For simplicity, complain about front timeline */
	XLogFilePath(path, recoveryTargetTLI, log, seg);
	errno = ENOENT;
	ereport(emode,
			(errcode_for_file_access(),
		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
				  path, log, seg)));
	return -1;
}

/*
 * Attempt to retrieve the specified file from off-line archival storage.
 * If successful, fill "path" with its complete path (note that this will be
 * a temp file name that doesn't follow the normal naming convention), and
 * return TRUE.
 *
 * If not successful, fill "path" with the name of the norm