*** a/contrib/Makefile
--- b/contrib/Makefile
***************
*** 31,36 **** SUBDIRS = \
--- 31,37 ----
  		passwordcheck	\
  		pg_archivecleanup \
  		pg_buffercache	\
+ 		pg_computemaxlsn \
  		pg_freespacemap \
  		pg_standby	\
  		pg_stat_statements \
*** /dev/null
--- b/contrib/pg_computemaxlsn/Makefile
***************
*** 0 ****
--- 1,22 ----
+ # contrib/pg_computemaxlsn/Makefile
+ 
+ PGFILEDESC = "pg_computemaxlsn - an utility to find max LSN from data pages"
+ PGAPPICON = win32
+ 
+ PROGRAM  = pg_computemaxlsn
+ OBJS = pg_computemaxlsn.o $(WIN32RES)
+ 
+ PG_CPPFLAGS  = -I$(srcdir)
+ PG_LIBS = $(libpq_pgport)
+ 
+ 
+ ifdef USE_PGXS
+ PG_CONFIG = pg_config
+ PGXS := $(shell $(PG_CONFIG) --pgxs)
+ include $(PGXS)
+ else
+ subdir = contrib/pg_computemaxlsn
+ top_builddir = ../..
+ include $(top_builddir)/src/Makefile.global
+ include $(top_srcdir)/contrib/contrib-global.mk
+ endif
*** /dev/null
--- b/contrib/pg_computemaxlsn/pg_computemaxlsn.c
***************
*** 0 ****
--- 1,430 ----
+ /*-------------------------------------------------------------------------
+  *
+  * pg_computemaxlsn.c
+  *	  A utility to compute the maximum LSN in data pages
+  *
+  * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+  * Portions Copyright (c) 1994, Regents of the University of California
+  *
+  * IDENTIFICATION
+  * contrib/pg_computemaxlsn/pg_computemaxlsn.c
+  *
+  *-------------------------------------------------------------------------
+  */
+ 
+ /*
+  * We have to use postgres.h not postgres_fe.h here, because there's so much
+  * backend-only stuff for reading data files we need.  But we need a
+  * frontend-ish environment otherwise.	Hence this ugly hack.
+  */
+ #define FRONTEND 1
+ 
+ #include "postgres.h"
+ 
+ #include <dirent.h>
+ #include <fcntl.h>
+ #include <locale.h>
+ #include <sys/stat.h>
+ #include <sys/time.h>
+ #include <time.h>
+ #include <unistd.h>
+ 
+ #include "getopt_long.h"
+ 
+ #include "access/xlog_internal.h"
+ #include "catalog/catalog.h"
+ #include "storage/bufpage.h"
+ #include "storage/fd.h"
+ 
+ /* Page header size */
+ #define PAGEHDRSZ (sizeof(PageHeaderData))
+ 
+ extern int	optind;
+ extern char *optarg;
+ static const char *progname;
+ static int	quiet = false;
+ 
+ static bool FindMaxLSNinFile(char *filename, XLogRecPtr *maxlsn);
+ static bool FindMaxLSNinDir(char *path, XLogRecPtr *maxlsn);
+ static bool FindMaxLSNinPgData(char *pgdatapath, XLogRecPtr *maxlsn);
+ static void usage(void);
+ 
+ /*
+  * This function validates the given cluster directory - we search for a
+  * small set of subdirectories that we expect to find in a valid data directory.
+  * directory. If any of the subdirectories are missing, then it treats as a
+  * normal directory.
+  */
+ static bool
+ check_data_dir(const char *pg_data)
+ {
+ 	char		subDirName[MAXPGPATH];
+ 	int			dnum;
+ 
+ 	/* start check with top-most directory */
+ 	const char *requiredSubdirs[] = {"", "base", "global", "pg_tblspc",
+ 		"pg_multixact", "pg_subtrans", "pg_clog", "pg_twophase",
+ 	"pg_xlog"};
+ 
+ 	for (dnum = 0; dnum < lengthof(requiredSubdirs); ++dnum)
+ 	{
+ 		struct stat statBuf;
+ 
+ 		snprintf(subDirName, sizeof(subDirName), "%s%s%s", pg_data,
+ 		/* Win32 can't stat() a directory with a trailing slash. */
+ 				 *requiredSubdirs[dnum] ? "/" : "",
+ 				 requiredSubdirs[dnum]);
+ 
+ 		if (stat(subDirName, &statBuf) != 0
+ 			|| (!S_ISDIR(statBuf.st_mode)))
+ 			return false;
+ 	}
+ 
+ 	return true;
+ }
+ 
+ /*
+  * relfilenode name validation.
+  * Format with_ext == true	[0-9]+[ \w | _vm | _fsm | _init ][\.][0-9]*
+  *		  with_ext == false [0-9]+
+  */
+ static bool
+ validateRelfilenodename(char *name)
+ {
+ 	int			pos = 0;
+ 
+ 	while ((name[pos] >= '0') && (name[pos] <= '9'))
+ 		pos++;
+ 
+ 	if (name[pos] == '_')
+ 	{
+ 		pos++;
+ 		while ((name[pos] >= 'a') && (name[pos] <= 'z'))
+ 			pos++;
+ 	}
+ 	if (name[pos] == '.')
+ 	{
+ 		pos++;
+ 		while ((name[pos] >= '0') && (name[pos] <= '9'))
+ 			pos++;
+ 	}
+ 
+ 	if (name[pos] == 0)
+ 		return true;
+ 
+ 	return false;
+ }
+ 
+ int
+ main(int argc, char *argv[])
+ {
+ 	static struct option long_options[] = {
+ 		{"quiet", no_argument, NULL, 'q'},
+ 		{NULL, 0, NULL, 0}
+ 	};
+ 	int			optindex;
+ 	int			c;
+ 	char	   *LsnSearchPath = NULL;
+ 	XLogRecPtr	maxLSN = 0;
+ 	XLogSegNo	logSegNo = 0;
+ 	bool		result = true;
+ 	struct stat statbuf;
+ 
+ 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_computemaxlsn"));
+ 
+ 	progname = get_progname(argv[0]);
+ 
+ 	if (argc > 1)
+ 	{
+ 		if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
+ 		{
+ 			usage();
+ 			exit(0);
+ 		}
+ 		if (strcmp(argv[1], "--version") == 0 || strcmp(argv[1], "-V") == 0)
+ 		{
+ 			puts("pg_computemaxlsn (PostgreSQL) " PG_VERSION);
+ 			exit(0);
+ 		}
+ 	}
+ 
+ 	while ((c = getopt_long(argc, argv, "q", long_options, &optindex)) != -1)
+ 	{
+ 		switch (c)
+ 		{
+ 			case 'q':
+ 				quiet = true;
+ 				break;
+ 			default:
+ 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
+ 				exit(1);
+ 		}
+ 	}
+ 
+ 	/* Loop over all input arguements */
+ 	do
+ 	{
+ 		if (optind < argc)
+ 			LsnSearchPath = argv[optind];
+ 		else
+ 			LsnSearchPath = getenv("PGDATA");
+ 
+ 		if (LsnSearchPath == NULL)
+ 		{
+ 			fprintf(stderr, _("%s: no file/directory specified\n"), progname);
+ 			fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
+ 			exit(1);
+ 		}
+ 
+ 		maxLSN = 0;
+ 
+ 		/* Check for the provided search path is a data directory? */
+ 		if (check_data_dir(LsnSearchPath))
+ 		{
+ 			result = FindMaxLSNinPgData(LsnSearchPath, &maxLSN);
+ 		}
+ 		else
+ 		{
+ 			if (lstat(LsnSearchPath, &statbuf) < 0)
+ 			{
+ 				if (errno == ENOENT)
+ 				{
+ 					fprintf(stderr, _("%s: file or directory \"%s\" does not exists.\n"),
+ 							progname, LsnSearchPath);
+ 				}
+ 				else
+ 				{
+ 					fprintf(stderr, _("%s: could not stat file or directory \"%s\": %s\n"),
+ 							progname, LsnSearchPath, strerror(errno));
+ 				}
+ 				exit(1);
+ 			}
+ 
+ 			if (S_ISREG(statbuf.st_mode))
+ 				result = FindMaxLSNinFile(LsnSearchPath, &maxLSN);
+ 			else
+ 				result = FindMaxLSNinDir(LsnSearchPath, &maxLSN);
+ 		}
+ 
+ 		if (!result)
+ 		{
+ 			/* Message already provided, simply exit */
+ 			exit(1);
+ 		}
+ 
+ 		XLByteToSeg(maxLSN, logSegNo);
+ 
+ 		printf("Maximum LSN found in \"%s\" is: %X/%X \n"
+ 			   "WAL segment file name (fileid,seg): %X/%X\n",
+ 			   LsnSearchPath, (uint32) (maxLSN >> 32), (uint32) maxLSN,
+ 			   (uint32) (logSegNo >> 32), (uint32) (logSegNo));
+ 	} while (++optind < argc);
+ 
+ 	return 0;
+ }
+ 
+ 
+ /*
+  * Read the maximum LSN number in the one of data file (relnode file).
+  */
+ static bool
+ FindMaxLSNinFile(char *filename, XLogRecPtr *maxlsn)
+ {
+ 	XLogRecPtr	pagelsn;
+ 	off_t		len,
+ 				seekpos;
+ 	uint32		nblocks,
+ 				blocknum;
+ 	char		buffer[PAGEHDRSZ];
+ 	int			nbytes;
+ 	int			fd;
+ 	XLogRecPtr	filemaxlsn = 0;
+ 	uint32		filemaxlsn_block = 0;
+ 
+ 	if ((fd = open(filename, O_RDONLY | PG_BINARY, 0)) < 0)
+ 	{
+ 		/*
+ 		 * If file does not exist or we can't read it. give error
+ 		 */
+ 		fprintf(stderr, _("%s: could not open file \"%s\" for reading: %s\n"),
+ 				progname, filename, strerror(errno));
+ 		return false;
+ 	}
+ 
+ 	/* Calculate the number of pages in file */
+ 	len = lseek(fd, 0L, SEEK_END);
+ 	if (len < 0)
+ 	{
+ 		close(fd);
+ 		fprintf(stderr, _("%s: file \"%s\" for seeking: %s\n"),
+ 				progname, filename, strerror(errno));
+ 		return false;
+ 	}
+ 
+ 	nblocks = (len / BLCKSZ);
+ 	if (nblocks > RELSEG_SIZE)
+ 	{
+ 		/*
+ 		 * In one relfilenode file length can't be more that RELSEG_SIZE
+ 		 */
+ 		close(fd);
+ 		fprintf(stderr, _("%s: file \"%s\" length is more than segment size: %d.\n"),
+ 				progname, filename, RELSEG_SIZE);
+ 		return false;
+ 	}
+ 
+ 	/*
+ 	 * Read the only page header and find the LSN of the page and continue to
+ 	 * next page.
+ 	 */
+ 	seekpos = 0;
+ 	for (blocknum = 0; blocknum < nblocks; blocknum++)
+ 	{
+ 		len = lseek(fd, seekpos, SEEK_SET);
+ 		if (len != seekpos)
+ 		{
+ 			close(fd);
+ 			fprintf(stderr, _("%s: could not seek to offset %u in file \"%s\": %s\n"),
+ 					progname, blocknum, filename, strerror(errno));
+ 			return false;
+ 		}
+ 
+ 		nbytes = read(fd, buffer, PAGEHDRSZ);
+ 		if (nbytes < 0)
+ 		{
+ 			close(fd);
+ 			fprintf(stderr, _("%s: could not read file \"%s\" at offset %u: %s\n"),
+ 					progname, filename, blocknum, strerror(errno));
+ 			return false;
+ 		}
+ 
+ 		/*
+ 		 * Remember this lsn as the highest (if it is)
+ 		 */
+ 		pagelsn = PageGetLSN(buffer);
+ 		if (filemaxlsn < pagelsn)
+ 		{
+ 			filemaxlsn = pagelsn;
+ 			filemaxlsn_block = blocknum;
+ 		}
+ 
+ 		seekpos += (off_t) BLCKSZ;
+ 	}
+ 
+ 	close(fd);
+ 
+ 	if (*maxlsn < filemaxlsn)
+ 		*maxlsn = filemaxlsn;
+ 
+ 	if (!quiet)
+ 		printf("Highest LSN for file:\"%s\" is: %X/%X in block %u\n",
+ 			   filename, (uint32) (filemaxlsn >> 32), (uint32) filemaxlsn,
+ 			   filemaxlsn_block);
+ 
+ 	return true;
+ }
+ 
+ /*
+  * Read the maximum LSN number in current directory; including sub directories
+  * and links.
+  */
+ static bool
+ FindMaxLSNinDir(char *path, XLogRecPtr *maxlsn)
+ {
+ 	DIR		   *dir;
+ 	struct dirent *de;
+ 	char		pathbuf[MAXPGPATH];
+ 	struct stat statbuf;
+ 	bool		result = true;
+ 
+ 	dir = opendir(path);
+ 	if (NULL == dir)
+ 	{
+ 		fprintf(stderr, _("%s: could not open directory \"%s\": %s\n"),
+ 				progname, path, strerror(errno));
+ 		return false;
+ 	}
+ 
+ 	while ((de = readdir(dir)) != NULL)
+ 	{
+ 		/* Skip special stuff */
+ 		if (strcmp(de->d_name, ".") == 0 || strcmp(de->d_name, "..") == 0)
+ 			continue;
+ 
+ 		/* Skip temporary files */
+ 		if (strncmp(de->d_name,
+ 					PG_TEMP_FILE_PREFIX,
+ 					strlen(PG_TEMP_FILE_PREFIX)) == 0)
+ 			continue;
+ 
+ 		/*
+ 		 * Skip all invalid files, and read remaining relfilenode files
+ 		 */
+ 		if (!validateRelfilenodename(de->d_name))
+ 			continue;
+ 
+ 		snprintf(pathbuf, MAXPGPATH, "%s/%s", path, de->d_name);
+ 
+ 		if (lstat(pathbuf, &statbuf) != 0)
+ 		{
+ 			if (errno != ENOENT)
+ 				fprintf(stderr, _("%s: could not stat file or directory \"%s\": %s\n"),
+ 						progname, pathbuf, strerror(errno));
+ 
+ 			/* If the file went away while scanning, it's no error. */
+ 			continue;
+ 		}
+ 
+ 		if (S_ISREG(statbuf.st_mode))
+ 		{
+ 			if (!FindMaxLSNinFile(pathbuf, maxlsn))
+ 				result = false;
+ 		}
+ 		else
+ 		{
+ 			if (!FindMaxLSNinDir(pathbuf, maxlsn))
+ 				result = false;
+ 		}
+ 	}
+ 
+ 	closedir(dir);
+ 	return result;
+ }
+ 
+ 
+ /*
+  * Read the maximum LSN number in the DATA directory.
+  */
+ static bool
+ FindMaxLSNinPgData(char *pgdatapath, XLogRecPtr *maxlsn)
+ {
+ 	char		pathbuf[MAXPGPATH];
+ 	bool		result = true;
+ 
+ 	/* scan all the relfilenodes in data directory */
+ 	snprintf(pathbuf, MAXPGPATH, "%s/global", pgdatapath);
+ 	if (!FindMaxLSNinDir(pathbuf, maxlsn))
+ 		result = false;
+ 
+ 	snprintf(pathbuf, MAXPGPATH, "%s/base", pgdatapath);
+ 	if (!FindMaxLSNinDir(pathbuf, maxlsn))
+ 		result = false;
+ 
+ 	snprintf(pathbuf, MAXPGPATH, "%s/pg_tblspc", pgdatapath);
+ 	if (!FindMaxLSNinDir(pathbuf, maxlsn))
+ 		result = false;
+ 
+ 	return result;
+ }
+ 
+ static void
+ usage(void)
+ {
+ 	printf(_("%s compute the maximum LSN in PostgreSQL data pages.\n\n"), progname);
+ 	printf(_("Usage:\n  %s [OPTION] [FILE/DIRECTORY...]\n\n"), progname);
+ 	printf(_("Options:\n"));
+ 	printf(_("  -q, --quiet        stops the output of highest LSN in a file\n"));
+ 	printf(_("  -V, --version      output version information, then exit\n"));
+ 	printf(_("  -?, --help         show this help, then exit\n"));
+ 	printf(_("\nReport bugs to <pgsql-bugs@postgresql.org>.\n"));
+ }
*** a/doc/src/sgml/contrib.sgml
--- b/doc/src/sgml/contrib.sgml
***************
*** 208,212 **** pages.
--- 208,213 ----
   &pgtesttiming;
   &pgupgrade;
   &pgxlogdump;
+  &pgcomputemaxlsn;
   </sect1>
  </appendix>
*** a/doc/src/sgml/filelist.sgml
--- b/doc/src/sgml/filelist.sgml
***************
*** 124,129 ****
--- 124,130 ----
  <!ENTITY pgbench         SYSTEM "pgbench.sgml">
  <!ENTITY pgarchivecleanup SYSTEM "pgarchivecleanup.sgml">
  <!ENTITY pgbuffercache   SYSTEM "pgbuffercache.sgml">
+ <!ENTITY pgcomputemaxlsn   SYSTEM "pg_computemaxlsn.sgml">
  <!ENTITY pgcrypto        SYSTEM "pgcrypto.sgml">
  <!ENTITY pgfreespacemap  SYSTEM "pgfreespacemap.sgml">
  <!ENTITY pgrowlocks      SYSTEM "pgrowlocks.sgml">
*** /dev/null
--- b/doc/src/sgml/pg_computemaxlsn.sgml
***************
*** 0 ****
--- 1,100 ----
+ <!--
+ doc/src/sgml/pg_computemaxlsn.sgml
+ PostgreSQL documentation
+ -->
+ 
+ <refentry id="pgcomputemaxlsn">
+  <refmeta>
+   <refentrytitle><application>pg_computemaxlsn</application></refentrytitle>
+   <manvolnum>1</manvolnum>
+   <refmiscinfo>Application</refmiscinfo>
+  </refmeta>
+ 
+  <refnamediv>
+   <refname>pg_computemaxlsn</refname>
+   <refpurpose>computes the maximum LSN in database of a <productname>PostgreSQL</productname> database cluster</refpurpose>
+  </refnamediv>
+ 
+  <indexterm zone="pgcomputemaxlsn">
+   <primary>pg_computemaxlsn</primary>
+  </indexterm>
+ 
+  <refsynopsisdiv>
+   <cmdsynopsis>
+    <command>pg_computemaxlsn</command>
+    <arg choice="opt"><replaceable>option</replaceable></arg>
+    <arg rep="repeat"><replaceable>file or directory</replaceable></arg>
+   </cmdsynopsis>
+  </refsynopsisdiv>
+ 
+  <refsect1 id="R1-APP-PGCOMPUTEMAXLSN-1">
+   <title>Description</title>
+   <para>
+    <command>pg_computemaxlsn</command> computes maximun LSN from database pages
+    in the specified list of files or directories.
+   </para>
+ 
+   <para>
+    If user doesn't provide the file or directory to find the max lsn then
+    <command>pg_computemaxlsn</command> use the environment variable <envar>PGDATA</>
+    if exists otherwise reports an error.
+   </para>
+ 
+   <para>
+    The <option>-q</> and <option>--quiet</> options stops the print of
+    highest LSN in a file.
+   </para>
+ 
+   <para>
+    The <option>-V</> and <option>--version</> options
+    print the <application>pg_computemaxlsn</application> version and exit. The
+    options <option>-?</> and <option>--help</> show supported syntax, and exit.
+   </para>
+  </refsect1>
+ 
+  <refsect1>
+   <title>use cases</title>
+   <para>
+    This utility can be used to avoid more data corruption by finding out the
+    maximum lsn in the data directory. which is required by the <command>pg_resetxlog</command>
+    to provide the new WAL segment file name.
+   </para>
+ 
+   <para>
+    This utility can also be used to decide whether backup is required or not when the data page
+    in old-master precedes the last applied LSN in old-standby (i.e., new-master) at the
+    moment of the failover.
+   </para>
+  </refsect1>
+ 
+  <refsect1>
+   <title>Examples</title>
+   <screen>
+ pg_computemaxlsn> ./pg_computemaxlsn -q ../../../data/
+ Maximum LSN found in "../../../data/" is: 0/181B090
+ WAL segment file name (fileid,seg): 0/1
+   </screen>
+ 
+   <screen>
+ pg_computemaxlsn> ./pg_computemaxlsn -q ../../../data/base/126*
+ Maximum LSN found in "../../../data/base/12625" is: 0/17D5360
+ WAL segment file name (fileid,seg): 0/1
+ Maximum LSN found in "../../../data/base/12630" is: 0/181B090
+ WAL segment file name (fileid,seg): 0/1
+   </screen>
+  </refsect1>
+ 
+  <refsect1>
+   <title>Notes</title>
+   <para>
+    This utility just parse the header of the page and provides the LSN, please be sure
+    when using this tool on directory which is not a data directory.
+   </para>
+ 
+   <para>
+    If any error occurs during the finding of max LSN in the provided file or directory,
+    the max lsn is not printed. Once the reported problem solves need to run the tool again
+    for proper result.
+   </para>
+  </refsect1>
+ </refentry>
*** a/doc/src/sgml/ref/pg_resetxlog.sgml
--- b/doc/src/sgml/ref/pg_resetxlog.sgml
***************
*** 139,144 **** PostgreSQL documentation
--- 139,153 ----
        largest entry in <filename>pg_xlog</>, use <literal>-l 00000001000000320000004B</> or higher.
       </para>
  
+      <para>
+       If <command>pg_resetxlog</command> complains that it cannot determine
+       valid data for <filename>pg_control</>, and if you do not have or corrupted
+       WAL segment files in the directory <filename>pg_xlog</> under the data directory,
+       then to identify larger WAL segment file from data files we can use utility <command>pg_computemaxlsn</command>
+       by specifing file or folder or data directory. Once larger WAL segment file is found use <option>-l</> option
+       for setting the value.
+      </para>
+ 
       <note>
        <para>
         <command>pg_resetxlog</command> itself looks at the files in
*** a/src/tools/msvc/Mkvcbuild.pm
--- b/src/tools/msvc/Mkvcbuild.pm
***************
*** 43,49 **** my @contrib_uselibpgcommon = (
  	'pg_standby',    'pg_archivecleanup',
  	'pg_test_fsync', 'pg_test_timing',
  	'pg_upgrade',    'pg_xlogdump',
! 	'vacuumlo');
  my $contrib_extralibs = { 'pgbench' => ['wsock32.lib'] };
  my $contrib_extraincludes =
    { 'tsearch2' => ['contrib/tsearch2'], 'dblink' => ['src/backend'] };
--- 43,49 ----
  	'pg_standby',    'pg_archivecleanup',
  	'pg_test_fsync', 'pg_test_timing',
  	'pg_upgrade',    'pg_xlogdump',
! 	'vacuumlo', 	 'pg_computemaxlsn');
  my $contrib_extralibs = { 'pgbench' => ['wsock32.lib'] };
  my $contrib_extraincludes =
    { 'tsearch2' => ['contrib/tsearch2'], 'dblink' => ['src/backend'] };