pg_probackup/parsexlog.c

/*-------------------------------------------------------------------------
 *
 * parsexlog.c
 *	  Functions for reading Write-Ahead-Log
 *
 * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *-------------------------------------------------------------------------
 */

#include "postgres_fe.h"

#include "pg_arman.h"

#include <unistd.h>

#include "commands/dbcommands_xlog.h"
#include "catalog/storage_xlog.h"

/*
 * RmgrNames is an array of resource manager names, to make error messages
 * a bit nicer.
 */
#define PG_RMGR(symname,name,redo,desc,identify,startup,cleanup) \
  name,

static const char *RmgrNames[RM_MAX_ID + 1] = {
#include "access/rmgrlist.h"
};

static void extractPageInfo(XLogReaderState *record);

static int	xlogreadfd = -1;
static XLogSegNo xlogreadsegno = -1;
static char xlogfpath[MAXPGPATH];

typedef struct XLogPageReadPrivate
{
	const char *archivedir;
	TimeLineID	tli;
} XLogPageReadPrivate;

static int SimpleXLogPageRead(XLogReaderState *xlogreader,
				   XLogRecPtr targetPagePtr,
				   int reqLen, XLogRecPtr targetRecPtr, char *readBuf,
				   TimeLineID *pageTLI);

/*
 * Read WAL from the archive directory, starting from 'startpoint' on the
 * given timeline, until 'endpoint'. Make note of the data blocks touched
 * by the WAL records, and return them in a page map.
 */
void
extractPageMap(const char *archivedir, XLogRecPtr startpoint, TimeLineID tli,
			   XLogRecPtr endpoint)
{
	XLogRecord *record;
	XLogReaderState *xlogreader;
	char	   *errormsg;
	XLogPageReadPrivate private;

	private.archivedir = archivedir;
	private.tli = tli;
	xlogreader = XLogReaderAllocate(&SimpleXLogPageRead, &private);
	if (xlogreader == NULL)
		elog(ERROR, "out of memory");

	do
	{
		record = XLogReadRecord(xlogreader, startpoint, &errormsg);
		if (record == NULL)
		{
			XLogRecPtr	errptr;

			errptr = startpoint ? startpoint : xlogreader->EndRecPtr;

			if (errormsg)
				elog(ERROR, "could not read WAL record at %X/%X: %s",
						 (uint32) (errptr >> 32), (uint32) (errptr),
						 errormsg);
			else
				elog(ERROR, "could not read WAL record at %X/%X",
						 (uint32) (startpoint >> 32),
						 (uint32) (startpoint));
		}

		extractPageInfo(xlogreader);

		startpoint = InvalidXLogRecPtr; /* continue reading at next record */

	} while (xlogreader->ReadRecPtr != endpoint);

	XLogReaderFree(xlogreader);
	if (xlogreadfd != -1)
	{
		close(xlogreadfd);
		xlogreadfd = -1;
	}
}

/* XLogreader callback function, to read a WAL page */
static int
SimpleXLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr,
				   int reqLen, XLogRecPtr targetRecPtr, char *readBuf,
				   TimeLineID *pageTLI)
{
	XLogPageReadPrivate *private = (XLogPageReadPrivate *) xlogreader->private_data;
	uint32		targetPageOff;
	XLogSegNo	targetSegNo;

	XLByteToSeg(targetPagePtr, targetSegNo);
	targetPageOff = targetPagePtr % XLogSegSize;

	/*
	 * See if we need to switch to a new segment because the requested record
	 * is not in the currently open one.
	 */
	if (xlogreadfd >= 0 && !XLByteInSeg(targetPagePtr, xlogreadsegno))
	{
		close(xlogreadfd);
		xlogreadfd = -1;
	}

	XLByteToSeg(targetPagePtr, xlogreadsegno);

	if (xlogreadfd < 0)
	{
		char		xlogfname[MAXFNAMELEN];

		XLogFileName(xlogfname, private->tli, xlogreadsegno);
		snprintf(xlogfpath, MAXPGPATH, "%s/%s", private->archivedir,
				 xlogfname);
		elog(LOG, "opening WAL segment \"%s\"", xlogfpath);

		xlogreadfd = open(xlogfpath, O_RDONLY | PG_BINARY, 0);

		if (xlogreadfd < 0)
		{
			elog(WARNING, "could not open WAL segment \"%s\": %s",
				 xlogfpath, strerror(errno));
			return -1;
		}
	}

	/*
	 * At this point, we have the right segment open.
	 */
	Assert(xlogreadfd != -1);

	/* Read the requested page */
	if (lseek(xlogreadfd, (off_t) targetPageOff, SEEK_SET) < 0)
	{
		elog(WARNING, "could not seek in file \"%s\": %s", xlogfpath,
			 strerror(errno));
		return -1;
	}

	if (read(xlogreadfd, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
	{
		elog(WARNING, "could not read from file \"%s\": %s",
			 xlogfpath, strerror(errno));
		return -1;
	}

	Assert(targetSegNo == xlogreadsegno);

	*pageTLI = private->tli;
	return XLOG_BLCKSZ;
}

/*
 * Extract information on which blocks the current record modifies.
 */
static void
extractPageInfo(XLogReaderState *record)
{
	int			block_id;
	RmgrId		rmid = XLogRecGetRmid(record);
	uint8		info = XLogRecGetInfo(record);
	uint8		rminfo = info & ~XLR_INFO_MASK;

	/* Is this a special record type that I recognize? */

	if (rmid == RM_DBASE_ID && rminfo == XLOG_DBASE_CREATE)
	{
		/*
		 * New databases can be safely ignored. They would be completely
		 * copied if found.
		 */
	}
	else if (rmid == RM_DBASE_ID && rminfo == XLOG_DBASE_DROP)
	{
		/*
		 * An existing database was dropped. It is fine to ignore that
		 * they will be removed appropriately.
		 */
	}
	else if (rmid == RM_SMGR_ID && rminfo == XLOG_SMGR_CREATE)
	{
		/*
		 * We can safely ignore these. The file will be removed when
		 * combining the backups in the case of differential on.
		 */
	}
	else if (rmid == RM_SMGR_ID && rminfo == XLOG_SMGR_TRUNCATE)
	{
		/*
		 * We can safely ignore these. When we compare the sizes later on,
		 * we'll notice that they differ, and copy the missing tail from
		 * source system.
		 */
	}
	else if (info & XLR_SPECIAL_REL_UPDATE)
	{
		/*
		 * This record type modifies a relation file in some special way, but
		 * we don't recognize the type. That's bad - we don't know how to
		 * track that change.
		 */
		elog(ERROR, "WAL record modifies a relation, but record type is not recognized\n"
			 "lsn: %X/%X, rmgr: %s, info: %02X",
		  (uint32) (record->ReadRecPtr >> 32), (uint32) (record->ReadRecPtr),
				 RmgrNames[rmid], info);
	}

	for (block_id = 0; block_id <= record->max_block_id; block_id++)
	{
		RelFileNode rnode;
		ForkNumber	forknum;
		BlockNumber blkno;

		if (!XLogRecGetBlockTag(record, block_id, &rnode, &forknum, &blkno))
			continue;

		/* We only care about the main fork; others are copied in toto */
		if (forknum != MAIN_FORKNUM)
			continue;

		process_block_change(forknum, rnode, blkno);
	}
}