02-initdb-configurable-walsegsize_v2.patch

diff --git a/configure b/configure
index a2f9a25..13f1da2 100755
--- a/configure
+++ b/configure
@@ -821,7 +821,6 @@ enable_tap_tests
 with_blocksize
 with_segsize
 with_wal_blocksize
-with_wal_segsize
 with_CC
 enable_depend
 enable_cassert
@@ -1518,8 +1517,6 @@ Optional Packages:
   --with-segsize=SEGSIZE  set table segment size in GB [1]
   --with-wal-blocksize=BLOCKSIZE
                           set WAL block size in kB [8]
-  --with-wal-segsize=SEGSIZE
-                          set WAL segment size in MB [16]
   --with-CC=CMD           set compiler (deprecated)
   --with-icu              build with ICU support
   --with-tcl              build Tcl modules (PL/Tcl)
@@ -3732,58 +3729,6 @@ cat >>confdefs.h <<_ACEOF
 #define XLOG_BLCKSZ ${XLOG_BLCKSZ}
 _ACEOF
 
-
-#
-# WAL segment size
-#
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for WAL segment size" >&5
-$as_echo_n "checking for WAL segment size... " >&6; }
-
-
-
-# Check whether --with-wal-segsize was given.
-if test "${with_wal_segsize+set}" = set; then :
-  withval=$with_wal_segsize;
-  case $withval in
-    yes)
-      as_fn_error $? "argument required for --with-wal-segsize option" "$LINENO" 5
-      ;;
-    no)
-      as_fn_error $? "argument required for --with-wal-segsize option" "$LINENO" 5
-      ;;
-    *)
-      wal_segsize=$withval
-      ;;
-  esac
-
-else
-  wal_segsize=16
-fi
-
-
-case ${wal_segsize} in
-  1) ;;
-  2) ;;
-  4) ;;
-  8) ;;
- 16) ;;
- 32) ;;
- 64) ;;
- 128) ;;
- 256) ;;
- 512) ;;
- 1024) ;;
-  *) as_fn_error $? "Invalid WAL segment size. Allowed values are 1,2,4,8,16,32,64,128,256,512,1024." "$LINENO" 5
-esac
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: ${wal_segsize}MB" >&5
-$as_echo "${wal_segsize}MB" >&6; }
-
-
-cat >>confdefs.h <<_ACEOF
-#define XLOG_SEG_SIZE (${wal_segsize} * 1024 * 1024)
-_ACEOF
-
-
 #
 # C compiler
 #
diff --git a/configure.in b/configure.in
index e94fba5..241e89c 100644
--- a/configure.in
+++ b/configure.in
@@ -344,37 +344,6 @@ AC_DEFINE_UNQUOTED([XLOG_BLCKSZ], ${XLOG_BLCKSZ}, [
 ])
 
 #
-# WAL segment size
-#
-AC_MSG_CHECKING([for WAL segment size])
-PGAC_ARG_REQ(with, wal-segsize, [SEGSIZE], [set WAL segment size in MB [16]],
-             [wal_segsize=$withval],
-             [wal_segsize=16])
-case ${wal_segsize} in
-  1) ;;
-  2) ;;
-  4) ;;
-  8) ;;
- 16) ;;
- 32) ;;
- 64) ;;
- 128) ;;
- 256) ;;
- 512) ;;
- 1024) ;;
-  *) AC_MSG_ERROR([Invalid WAL segment size. Allowed values are 1,2,4,8,16,32,64,128,256,512,1024.])
-esac
-AC_MSG_RESULT([${wal_segsize}MB])
-
-AC_DEFINE_UNQUOTED([XLOG_SEG_SIZE], [(${wal_segsize} * 1024 * 1024)], [
- XLOG_SEG_SIZE is the size of a single WAL file.  This must be a power of 2
- and larger than XLOG_BLCKSZ (preferably, a great deal larger than
- XLOG_BLCKSZ).
-
- Changing XLOG_SEG_SIZE requires an initdb.
-])
-
-#
 # C compiler
 #
 
diff --git a/contrib/pg_standby/pg_standby.c b/contrib/pg_standby/pg_standby.c
index d7fa2a8..349f1ca 100644
--- a/contrib/pg_standby/pg_standby.c
+++ b/contrib/pg_standby/pg_standby.c
@@ -33,9 +33,12 @@
 #include "pg_getopt.h"
 
 #include "access/xlog_internal.h"
+#include "access/xlogreader.h"
 
 const char *progname;
 
+int			XLogSegSize;
+
 /* Options and defaults */
 int			sleeptime = 5;		/* amount of time to sleep between file checks */
 int			waittime = -1;		/* how long we have been waiting, -1 no wait
@@ -100,6 +103,72 @@ int			nextWALFileType;
 
 struct stat stat_buf;
 
+static bool SetWALFileNameForCleanup(void);
+
+/* Set wal segment size from the WAL file specified by WALFilePath */
+static bool
+RetrieveXLogSegSize(void)
+{
+	bool		ret_val = false;
+	int			fd;
+	char	   *buf = (char *) malloc(XLOG_BLCKSZ);
+
+	/* Already set a valid XLogSegSize? */
+	if (IsValidXLogSegSize(XLogSegSize))
+		return true;
+
+	if ((fd = open(WALFilePath, O_RDWR, 0)) < 0)
+	{
+		fprintf(stderr, "%s: couldn't open WAL file \"%s\"\n",
+				progname, WALFilePath);
+		return false;
+	}
+	if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+	{
+		XLogPageHeader hdr = (XLogPageHeader) buf;
+		XLogLongPageHeader longhdr = (XLogLongPageHeader) hdr;
+
+		XLogSegSize = longhdr->xlp_seg_size;
+
+		if (IsValidXLogSegSize(XLogSegSize))
+		{
+			/* successfully retrieved WAL segment size */
+			ret_val = true;
+
+			/* check if clean up is necessary */
+			need_cleanup = SetWALFileNameForCleanup();
+			if (debug)
+			{
+				fprintf(stderr,
+						_("WAL segment size:     %d \n"), XLogSegSize);
+				fprintf(stderr, "Keep archive history: ");
+
+				if (need_cleanup)
+					fprintf(stderr, "%s and later\n",
+							exclusiveCleanupFileName);
+				else
+					fprintf(stderr, "no cleanup required\n");
+			}
+		}
+		else
+			fprintf(stderr,
+					"%s: WAL segment size must be a power of two between 1MB and 1GB, but the WAL file header specifies %d bytes\n",
+					progname, XLogSegSize);
+		close(fd);
+	}
+	else
+	{
+		if (errno != 0)
+			fprintf(stderr, "could not read file \"%s\": %s",
+				WALFilePath, strerror(errno));
+		else
+			fprintf(stderr, "not enough data in file \"%s\"", WALFilePath);
+	}
+
+	fflush(stderr);
+	return ret_val;
+}
+
 /* =====================================================================
  *
  *		  Customizable section
@@ -184,7 +253,9 @@ CustomizableNextWALFileReady(void)
 			nextWALFileType = XLOG_BACKUP_LABEL;
 			return true;
 		}
-		else if (stat_buf.st_size == XLOG_SEG_SIZE)
+		else if (!RetrieveXLogSegSize())
+			return false;
+		else if (stat_buf.st_size == XLogSegSize)
 		{
 #ifdef WIN32
 
@@ -204,7 +275,7 @@ CustomizableNextWALFileReady(void)
 		/*
 		 * If still too small, wait until it is the correct size
 		 */
-		if (stat_buf.st_size > XLOG_SEG_SIZE)
+		if (stat_buf.st_size > XLogSegSize)
 		{
 			if (debug)
 			{
@@ -218,8 +289,6 @@ CustomizableNextWALFileReady(void)
 	return false;
 }
 
-#define MaxSegmentsPerLogFile ( 0xFFFFFFFF / XLOG_SEG_SIZE )
-
 static void
 CustomizableCleanupPriorWALFiles(void)
 {
@@ -315,6 +384,7 @@ SetWALFileNameForCleanup(void)
 	uint32		log_diff = 0,
 				seg_diff = 0;
 	bool		cleanup = false;
+	int			MaxSegmentsPerLogFile = (0xFFFFFFFF / XLogSegSize);
 
 	if (restartWALFileName)
 	{
@@ -708,8 +778,6 @@ main(int argc, char **argv)
 
 	CustomizableInitialize();
 
-	need_cleanup = SetWALFileNameForCleanup();
-
 	if (debug)
 	{
 		fprintf(stderr, "Trigger file:         %s\n", triggerPath ? triggerPath : "<not set>");
@@ -721,11 +789,6 @@ main(int argc, char **argv)
 		fprintf(stderr, "Max wait interval:    %d %s\n",
 				maxwaittime, (maxwaittime > 0 ? "seconds" : "forever"));
 		fprintf(stderr, "Command for restore:  %s\n", restoreCommand);
-		fprintf(stderr, "Keep archive history: ");
-		if (need_cleanup)
-			fprintf(stderr, "%s and later\n", exclusiveCleanupFileName);
-		else
-			fprintf(stderr, "no cleanup required\n");
 		fflush(stderr);
 	}
 
diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index 95aeb35..bd55e8b 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -562,7 +562,7 @@ tar -cf backup.tar /usr/local/pgsql/data
     produces an indefinitely long sequence of WAL records.  The system
     physically divides this sequence into WAL <firstterm>segment
     files</>, which are normally 16MB apiece (although the segment size
-    can be altered when building <productname>PostgreSQL</>).  The segment
+    can be altered during <application>initdb</>).  The segment
     files are given numeric names that reflect their position in the
     abstract WAL sequence.  When not using WAL archiving, the system
     normally creates just a few segment files and then
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index 12866b4..0f512ba 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1059,20 +1059,6 @@ su - postgres
       </varlistentry>
 
       <varlistentry>
-       <term><option>--with-wal-segsize=<replaceable>SEGSIZE</replaceable></option></term>
-       <listitem>
-        <para>
-         Set the <firstterm>WAL segment size</>, in megabytes.  This is
-         the size of each individual file in the WAL log.  It may be useful
-         to adjust this size to control the granularity of WAL log shipping.
-         The default size is 16 megabytes.
-         The value must be a power of 2 between 1 and 1024 (megabytes).
-         Note that changing this value requires an initdb.
-        </para>
-       </listitem>
-      </varlistentry>
-
-      <varlistentry>
        <term><option>--with-wal-blocksize=<replaceable>BLOCKSIZE</replaceable></option></term>
        <listitem>
         <para>
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 6efb2e4..732feca 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -316,6 +316,21 @@ PostgreSQL documentation
      </varlistentry>
 
      <varlistentry>
+       <term><option>--wal-segsize=<replaceable>SEGSIZE</replaceable></option></term>
+       <listitem>
+        <para>
+         Set the <firstterm>WAL segment size</>, in megabytes.  This is
+         the size of each individual file in the WAL log.  It may be useful
+         to adjust this size to control the granularity of WAL log shipping.
+         This option can only be set during initialization, and cannot be
+         changed later.
+         The default size is 16 megabytes.
+         The value must be a power of 2 between 1 and 1024 (megabytes).
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
       <term><option>-X <replaceable class="parameter">directory</replaceable></option></term>
       <term><option>--waldir=<replaceable class="parameter">directory</replaceable></option></term>
       <listitem>
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 940c37b..58c13d3 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -752,13 +752,12 @@
    <acronym>WAL</acronym> logs are stored in the directory
    <filename>pg_wal</filename> under the data directory, as a set of
    segment files, normally each 16 MB in size (but the size can be changed
-   by altering the <option>--with-wal-segsize</> configure option when
-   building the server).  Each segment is divided into pages, normally
-   8 kB each (this size can be changed via the <option>--with-wal-blocksize</>
-   configure option).  The log record headers are described in
-   <filename>access/xlogrecord.h</filename>; the record content is dependent
-   on the type of event that is being logged.  Segment files are given
-   ever-increasing numbers as names, starting at
+   by altering the <option>--wal-segsize</> initdb option).  Each segment is
+   divided into pages, normally 8 kB each (this size can be changed via the
+   <option>--with-wal-blocksize</> configure option).  The log record headers
+   are described in <filename>access/xlogrecord.h</filename>; the record content
+   is dependent on the type of event that is being logged.  Segment files are
+   given ever-increasing numbers as names, starting at
    <filename>000000010000000000000000</filename>.  The numbers do not wrap,
    but it will take a very, very long time to exhaust the
    available stock of numbers.
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index b753d07..4e7c50d 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -110,6 +110,8 @@ int			wal_retrieve_retry_interval = 5000;
 bool		XLOG_DEBUG = false;
 #endif
 
+int			XLogSegSize = DEFAULT_XLOG_SEG_SIZE;
+
 /*
  * Number of WAL insertion locks to use. A higher value allows more insertions
  * to happen concurrently, but adds some CPU overhead to flushing the WAL,
@@ -731,14 +733,16 @@ static ControlFileData *ControlFile = NULL;
 	(((recptr) / XLOG_BLCKSZ) % (XLogCtl->XLogCacheBlck + 1))
 
 /*
- * These are the number of bytes in a WAL page and segment usable for WAL data.
+ * These are the number of bytes in a WAL page usable for WAL data.
  */
 #define UsableBytesInPage (XLOG_BLCKSZ - SizeOfXLogShortPHD)
-#define UsableBytesInSegment ((XLOG_SEG_SIZE / XLOG_BLCKSZ) * UsableBytesInPage - (SizeOfXLogLongPHD - SizeOfXLogShortPHD))
 
 /* Convert min_wal_size_mb and max wal_size_mb to equivalent segment count */
 #define ConvertToXSegs(x)	\
-	(x / (XLOG_SEG_SIZE / (1024 * 1024)))
+	(x / (XLogSegSize / (1024 * 1024)))
+
+/* The number of bytes in a WAL segment usable for WAL data. */
+static int	UsableBytesInSegment;
 
 /*
  * Private, possibly out-of-date copy of shared LogwrtResult.
@@ -1309,8 +1313,8 @@ ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos, XLogRecPtr *PrevPtr)
 	*StartPos = XLogBytePosToRecPtr(startbytepos);
 	*EndPos = XLogBytePosToEndRecPtr(endbytepos);
 
-	segleft = XLOG_SEG_SIZE - (XLogSegmentOffset(*EndPos));
-	if (segleft != XLOG_SEG_SIZE)
+	segleft = XLogSegSize - (XLogSegmentOffset(*EndPos));
+	if (segleft != XLogSegSize)
 	{
 		/* consume the rest of the segment */
 		*EndPos += segleft;
@@ -1539,7 +1543,7 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
 
 		/*
 		 * We do this one page at a time, to make sure we don't deadlock
-		 * against ourselves if wal_buffers < XLOG_SEG_SIZE.
+		 * against ourselves if wal_buffers < XLogSegSize.
 		 */
 		Assert(XLogSegmentOffset(EndPos) == 0);
 
@@ -2260,8 +2264,8 @@ XLOGfileslop(XLogRecPtr PriorRedoPtr)
 	 * correspond to. Always recycle enough segments to meet the minimum, and
 	 * remove enough segments to stay below the maximum.
 	 */
-	minSegNo = PriorRedoPtr / XLOG_SEG_SIZE + ConvertToXSegs(min_wal_size_mb) - 1;
-	maxSegNo = PriorRedoPtr / XLOG_SEG_SIZE + ConvertToXSegs(max_wal_size_mb) - 1;
+	minSegNo = PriorRedoPtr / XLogSegSize + ConvertToXSegs(min_wal_size_mb) - 1;
+	maxSegNo = PriorRedoPtr / XLogSegSize + ConvertToXSegs(max_wal_size_mb) - 1;
 
 	/*
 	 * Between those limits, recycle enough segments to get us through to the
@@ -2290,7 +2294,7 @@ XLOGfileslop(XLogRecPtr PriorRedoPtr)
 	/* add 10% for good measure. */
 	distance *= 1.10;
 
-	recycleSegNo = (XLogSegNo) ceil(((double) PriorRedoPtr + distance) / XLOG_SEG_SIZE);
+	recycleSegNo = (XLogSegNo) ceil(((double) PriorRedoPtr + distance) / XLogSegSize);
 
 	if (recycleSegNo < minSegNo)
 		recycleSegNo = minSegNo;
@@ -4399,7 +4403,7 @@ WriteControlFile(void)
 	ControlFile->blcksz = BLCKSZ;
 	ControlFile->relseg_size = RELSEG_SIZE;
 	ControlFile->xlog_blcksz = XLOG_BLCKSZ;
-	ControlFile->xlog_seg_size = XLOG_SEG_SIZE;
+	ControlFile->xlog_seg_size = XLogSegSize;
 
 	ControlFile->nameDataLen = NAMEDATALEN;
 	ControlFile->indexMaxKeys = INDEX_MAX_KEYS;
@@ -4467,6 +4471,7 @@ ReadControlFile(void)
 {
 	pg_crc32c	crc;
 	int			fd;
+	static char wal_segsz_str[20];
 
 	/*
 	 * Read data...
@@ -4569,13 +4574,6 @@ ReadControlFile(void)
 						   " but the server was compiled with XLOG_BLCKSZ %d.",
 						   ControlFile->xlog_blcksz, XLOG_BLCKSZ),
 				 errhint("It looks like you need to recompile or initdb.")));
-	if (ControlFile->xlog_seg_size != XLOG_SEG_SIZE)
-		ereport(FATAL,
-				(errmsg("database files are incompatible with server"),
-				 errdetail("The database cluster was initialized with XLOG_SEG_SIZE %d,"
-						   " but the server was compiled with XLOG_SEG_SIZE %d.",
-						   ControlFile->xlog_seg_size, XLOG_SEG_SIZE),
-				 errhint("It looks like you need to recompile or initdb.")));
 	if (ControlFile->nameDataLen != NAMEDATALEN)
 		ereport(FATAL,
 				(errmsg("database files are incompatible with server"),
@@ -4637,6 +4635,29 @@ ReadControlFile(void)
 				 errhint("It looks like you need to recompile or initdb.")));
 #endif
 
+	XLogSegSize = ControlFile->xlog_seg_size;
+
+	if (!IsValidXLogSegSize(XLogSegSize))
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg("WAL segment size must be a power of two between 1MB and 1GB, but the control file specifies %d bytes",
+							   XLogSegSize)));
+
+	snprintf(wal_segsz_str, sizeof(wal_segsz_str), "%d", XLogSegSize);
+	SetConfigOption("wal_segment_size", wal_segsz_str, PGC_INTERNAL,
+					PGC_S_OVERRIDE);
+
+	/* check and update variables dependent on XLogSegSize */
+	if (ConvertToXSegs(min_wal_size_mb) < 2)
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg("\"min_wal_size\" must be at least twice \"wal_segment_size\".")));
+
+	if (ConvertToXSegs(max_wal_size_mb) < 2)
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg("\"max_wal_size\" must be at least twice \"wal_segment_size\".")));
+
+	CalculateUsableBytesInSegment();
+	CalculateCheckpointSegments();
+
 	/* Make the initdb settings visible as GUC variables, too */
 	SetConfigOption("data_checksums", DataChecksumsEnabled() ? "yes" : "no",
 					PGC_INTERNAL, PGC_S_OVERRIDE);
@@ -4757,8 +4778,8 @@ XLOGChooseNumBuffers(void)
 	int			xbuffers;
 
 	xbuffers = NBuffers / 32;
-	if (xbuffers > XLOG_SEG_SIZE / XLOG_BLCKSZ)
-		xbuffers = XLOG_SEG_SIZE / XLOG_BLCKSZ;
+	if (xbuffers > (XLogSegSize / XLOG_BLCKSZ))
+		xbuffers = (XLogSegSize / XLOG_BLCKSZ);
 	if (xbuffers < 8)
 		xbuffers = 8;
 	return xbuffers;
@@ -4817,6 +4838,17 @@ XLOGShmemSize(void)
 	{
 		char		buf[32];
 
+		/*
+		 * The calculation of XLOGbuffers requires the run-time parameter
+		 * XLogSegSize which is set from the control file. This value is
+		 * required to create the shared memory segment. Hence, temporarily
+		 * allocate space for reading the control file.
+		 */
+		if (!IsBootstrapProcessingMode())
+		{
+			ControlFile = palloc(sizeof(ControlFileData));
+			ReadControlFile();
+		}
 		snprintf(buf, sizeof(buf), "%d", XLOGChooseNumBuffers());
 		SetConfigOption("wal_buffers", buf, PGC_POSTMASTER, PGC_S_OVERRIDE);
 	}
@@ -4850,6 +4882,7 @@ XLOGShmemInit(void)
 				foundXLog;
 	char	   *allocptr;
 	int			i;
+	ControlFileData *temp_cfile;
 
 #ifdef WAL_DEBUG
 
@@ -4867,6 +4900,16 @@ XLOGShmemInit(void)
 	}
 #endif
 
+	/*
+	 * If we are not in bootstrap mode, ControlFile is already read. Copy it
+	 * to a temporary variable before reading it into shared memory later.
+	 */
+	if (!IsBootstrapProcessingMode())
+	{
+		temp_cfile = palloc(sizeof(ControlFileData));
+		memcpy(temp_cfile, ControlFile, sizeof(ControlFileData));
+	}
+
 	ControlFile = (ControlFileData *)
 		ShmemInitStruct("Control File", sizeof(ControlFileData), &foundCFile);
 	XLogCtl = (XLogCtlData *)
@@ -4935,12 +4978,11 @@ XLOGShmemInit(void)
 	InitSharedLatch(&XLogCtl->recoveryWakeupLatch);
 
 	/*
-	 * If we are not in bootstrap mode, pg_control should already exist. Read
-	 * and validate it immediately (see comments in ReadControlFile() for the
-	 * reasons why).
+	 * If we are not in bootstrap mode, copy the control file data from
+	 * temporary variable into the shared memory.
 	 */
 	if (!IsBootstrapProcessingMode())
-		ReadControlFile();
+		memcpy(ControlFile, temp_cfile, sizeof(ControlFileData));
 }
 
 /*
@@ -6188,6 +6230,16 @@ CheckRequiredParameterValues(void)
 }
 
 /*
+ * Calculate UsableBytesInSegment based on XLogSegSize
+ */
+void
+CalculateUsableBytesInSegment(void)
+{
+	UsableBytesInSegment = (XLogSegSize / XLOG_BLCKSZ * UsableBytesInPage) -
+		(SizeOfXLogLongPHD - SizeOfXLogShortPHD);
+}
+
+/*
  * This must be called ONCE during postmaster or standalone-backend startup
  */
 void
@@ -8150,6 +8202,9 @@ InitXLOGAccess(void)
 	ThisTimeLineID = XLogCtl->ThisTimeLineID;
 	Assert(ThisTimeLineID != 0 || IsBootstrapProcessingMode());
 
+	/* set XLogSegSize */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
 	/* Use GetRedoRecPtr to copy the RedoRecPtr safely */
 	(void) GetRedoRecPtr();
 	/* Also update our copy of doPageWrites. */
@@ -8480,7 +8535,7 @@ UpdateCheckPointDistanceEstimate(uint64 nbytes)
 	 * more.
 	 *
 	 * When checkpoints are triggered by max_wal_size, this should converge to
-	 * CheckpointSegments * XLOG_SEG_SIZE,
+	 * CheckpointSegments * XLogSegSize,
 	 *
 	 * Note: This doesn't pay any attention to what caused the checkpoint.
 	 * Checkpoints triggered manually with CHECKPOINT command, or by e.g.
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 60523d1..02e38f6 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -778,7 +778,7 @@ ValidXLogPageHeader(XLogReaderState *state, XLogRecPtr recptr,
 		else if (longhdr->xlp_seg_size != XLogSegSize)
 		{
 			report_invalid_record(state,
-								  "WAL file is from different database system: incorrect XLOG_SEG_SIZE in page header");
+								  "WAL file is from different database system: incorrect XLogSegSize in page header");
 			return false;
 		}
 		else if (longhdr->xlp_xlog_blcksz != XLOG_BLCKSZ)
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index 0453fd4..ba1348e 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -19,6 +19,7 @@
 
 #include "access/htup_details.h"
 #include "access/xact.h"
+#include "access/xlog_internal.h"
 #include "bootstrap/bootstrap.h"
 #include "catalog/index.h"
 #include "catalog/pg_collation.h"
@@ -222,7 +223,7 @@ AuxiliaryProcessMain(int argc, char *argv[])
 	/* If no -x argument, we are a CheckerProcess */
 	MyAuxProcType = CheckerProcess;
 
-	while ((flag = getopt(argc, argv, "B:c:d:D:Fkr:x:-:")) != -1)
+	while ((flag = getopt(argc, argv, "B:c:d:D:Fkr:x:X:-:")) != -1)
 	{
 		switch (flag)
 		{
@@ -257,6 +258,13 @@ AuxiliaryProcessMain(int argc, char *argv[])
 			case 'x':
 				MyAuxProcType = atoi(optarg);
 				break;
+			case 'X':
+				XLogSegSize = strtoul(optarg, NULL, 0);
+				if (!IsValidXLogSegSize(XLogSegSize))
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+							 errmsg("-X requires a power of 2 value between 1MB and 1GB")));
+				break;
 			case 'c':
 			case '-':
 				{
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 95180b2..67abedb 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -521,6 +521,7 @@ typedef struct
 	HANDLE		PostmasterHandle;
 	HANDLE		initial_signal_pipe;
 	HANDLE		syslogPipe[2];
+	int			XLogSegSize;
 #else
 	int			postmaster_alive_fds[2];
 	int			syslogPipe[2];
@@ -6008,6 +6009,7 @@ save_backend_variables(BackendParameters *param, Port *port,
 								 pgwin32_create_signal_listener(childPid),
 								 childProcess))
 		return false;
+	param->XLogSegSize = XLogSegSize;
 #else
 	memcpy(&param->postmaster_alive_fds, &postmaster_alive_fds,
 		   sizeof(postmaster_alive_fds));
@@ -6237,6 +6239,8 @@ restore_backend_variables(BackendParameters *param, Port *port)
 #ifdef WIN32
 	PostmasterHandle = param->PostmasterHandle;
 	pgwin32_initial_signal_pipe = param->initial_signal_pipe;
+	XLogSegSize = param->XLogSegSize;
+	CalculateUsableBytesInSegment();
 #else
 	memcpy(&postmaster_alive_fds, &param->postmaster_alive_fds,
 		   sizeof(postmaster_alive_fds));
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 246fea8..bc11658 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -514,7 +514,6 @@ static int	block_size;
 static int	segment_size;
 static int	wal_block_size;
 static bool data_checksums;
-static int	wal_segment_size;
 static bool integer_datetimes;
 static bool assert_enabled;
 
@@ -714,14 +713,16 @@ typedef struct
 #if XLOG_BLCKSZ < 1024 || XLOG_BLCKSZ > (1024*1024)
 #error XLOG_BLCKSZ must be between 1KB and 1MB
 #endif
-#if XLOG_SEG_SIZE < (1024*1024) || XLOG_SEG_SIZE > (1024*1024*1024)
-#error XLOG_SEG_SIZE must be between 1MB and 1GB
-#endif
 
 static const char *memory_units_hint = gettext_noop("Valid units for this parameter are \"kB\", \"MB\", \"GB\", and \"TB\".");
 
 static const unit_conversion memory_unit_conversion_table[] =
 {
+	{"GB", GUC_UNIT_BYT, 1024 * 1024 * 1024},
+	{"MB", GUC_UNIT_BYT, 1024 * 1024},
+	{"kB", GUC_UNIT_BYT, 1024},
+	{"B", GUC_UNIT_BYT, 1},
+
 	{"TB", GUC_UNIT_KB, 1024 * 1024 * 1024},
 	{"GB", GUC_UNIT_KB, 1024 * 1024},
 	{"MB", GUC_UNIT_KB, 1024},
@@ -2259,7 +2260,8 @@ static struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_MB
 		},
 		&min_wal_size_mb,
-		5 * (XLOG_SEG_SIZE / (1024 * 1024)), 2, MAX_KILOBYTES,
+		DEFAULT_MIN_WAL_SEGS * (DEFAULT_XLOG_SEG_SIZE / (1024 * 1024)),
+		2, MAX_KILOBYTES,
 		NULL, NULL, NULL
 	},
 
@@ -2270,7 +2272,8 @@ static struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_MB
 		},
 		&max_wal_size_mb,
-		64 * (XLOG_SEG_SIZE / (1024 * 1024)), 2, MAX_KILOBYTES,
+		DEFAULT_MAX_WAL_SEGS * (DEFAULT_XLOG_SEG_SIZE / (1024 * 1024)),
+		2, MAX_KILOBYTES,
 		NULL, assign_max_wal_size, NULL
 	},
 
@@ -2634,12 +2637,12 @@ static struct config_int ConfigureNamesInt[] =
 		{"wal_segment_size", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the number of pages per write ahead log segment."),
 			NULL,
-			GUC_UNIT_XBLOCKS | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
+			GUC_UNIT_BYT | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
 		},
-		&wal_segment_size,
-		(XLOG_SEG_SIZE / XLOG_BLCKSZ),
-		(XLOG_SEG_SIZE / XLOG_BLCKSZ),
-		(XLOG_SEG_SIZE / XLOG_BLCKSZ),
+		&XLogSegSize,
+		DEFAULT_XLOG_SEG_SIZE,
+		XLogSegMinSize,
+		XLogSegMaxSize,
 		NULL, NULL, NULL
 	},
 
@@ -2863,11 +2866,7 @@ static struct config_int ConfigureNamesInt[] =
 		{"track_activity_query_size", PGC_POSTMASTER, RESOURCES_MEM,
 			gettext_noop("Sets the size reserved for pg_stat_activity.query, in bytes."),
 			NULL,
-
-			/*
-			 * There is no _bytes_ unit, so the user can't supply units for
-			 * this.
-			 */
+			GUC_UNIT_BYT
 		},
 		&pgstat_track_activity_query_size,
 		1024, 100, 102400,
@@ -8113,6 +8112,9 @@ GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
 	{
 		switch (conf->flags & (GUC_UNIT_MEMORY | GUC_UNIT_TIME))
 		{
+			case GUC_UNIT_BYT:
+				values[2] = "B";
+				break;
 			case GUC_UNIT_KB:
 				values[2] = "kB";
 				break;
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index df5d2f3..1a79258 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -234,7 +234,7 @@
 
 #max_wal_senders = 10		# max number of walsender processes
 				# (change requires restart)
-#wal_keep_segments = 0		# in logfile segments, 16MB each; 0 disables
+#wal_keep_segments = 0		# in logfile segments; 0 disables
 #wal_sender_timeout = 60s	# in milliseconds; 0 disables
 
 #max_replication_slots = 10	# max number of replication slots
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 7303bbe..7fc2fc8 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -52,6 +52,7 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <math.h>
 #include <signal.h>
 #include <time.h>
 
@@ -59,6 +60,7 @@
 #include "sys/mman.h"
 #endif
 
+#include "access/xlog_internal.h"
 #include "catalog/catalog.h"
 #include "catalog/pg_authid.h"
 #include "catalog/pg_class.h"
@@ -141,6 +143,8 @@ static bool sync_only = false;
 static bool show_setting = false;
 static bool data_checksums = false;
 static char *xlog_dir = "";
+static char *str_wal_segment_size = "";
+static int  wal_segment_size;
 
 
 /* internal vars */
@@ -1000,6 +1004,25 @@ test_config_settings(void)
 }
 
 /*
+ * Calculate the default wal_size in proper unit.
+ */
+static char *
+pretty_wal_size(int segment_count)
+{
+	double		val = wal_segment_size / (1024 * 1024) * segment_count;
+	double		temp_val;
+	char	   *result = malloc(10);
+
+	temp_val = val / 1024;
+	if (ceilf(temp_val) == temp_val)
+		snprintf(result, 10, "%dGB", (int) temp_val);
+	else
+		snprintf(result, 10, "%dMB", (int) val);
+
+	return result;
+}
+
+/*
  * set up all the config files
  */
 static void
@@ -1043,6 +1066,15 @@ setup_config(void)
 	conflines = replace_token(conflines, "#port = 5432", repltok);
 #endif
 
+	/* set default max_wal_size and min_wal_size */
+	snprintf(repltok, sizeof(repltok), "min_wal_size = %s",
+			 pretty_wal_size(DEFAULT_MIN_WAL_SEGS));
+	conflines = replace_token(conflines, "#min_wal_size = 80MB", repltok);
+
+	snprintf(repltok, sizeof(repltok), "max_wal_size = %s",
+			 pretty_wal_size(DEFAULT_MAX_WAL_SEGS));
+	conflines = replace_token(conflines, "#max_wal_size = 1GB", repltok);
+
 	snprintf(repltok, sizeof(repltok), "lc_messages = '%s'",
 			 escape_quotes(lc_messages));
 	conflines = replace_token(conflines, "#lc_messages = 'C'", repltok);
@@ -1356,8 +1388,9 @@ bootstrap_template1(void)
 	unsetenv("PGCLIENTENCODING");
 
 	snprintf(cmd, sizeof(cmd),
-			 "\"%s\" --boot -x1 %s %s %s",
+			 "\"%s\" --boot -x1 -X %u %s %s %s",
 			 backend_exec,
+			 wal_segment_size,
 			 data_checksums ? "-k" : "",
 			 boot_options, talkargs);
 
@@ -2291,6 +2324,7 @@ usage(const char *progname)
 	printf(_("  -U, --username=NAME       database superuser name\n"));
 	printf(_("  -W, --pwprompt            prompt for a password for the new superuser\n"));
 	printf(_("  -X, --waldir=WALDIR       location for the write-ahead log directory\n"));
+	printf(_("      --wal-segsize=SIZE    size of wal segment size\n"));
 	printf(_("\nLess commonly used options:\n"));
 	printf(_("  -d, --debug               generate lots of debugging output\n"));
 	printf(_("  -k, --data-checksums      use data page checksums\n"));
@@ -2985,6 +3019,7 @@ main(int argc, char *argv[])
 		{"no-sync", no_argument, NULL, 'N'},
 		{"sync-only", no_argument, NULL, 'S'},
 		{"waldir", required_argument, NULL, 'X'},
+		{"wal-segsize", required_argument, NULL, 12},
 		{"data-checksums", no_argument, NULL, 'k'},
 		{NULL, 0, NULL, 0}
 	};
@@ -3118,6 +3153,9 @@ main(int argc, char *argv[])
 			case 'X':
 				xlog_dir = pg_strdup(optarg);
 				break;
+			case 12:
+				str_wal_segment_size = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
@@ -3180,6 +3218,30 @@ main(int argc, char *argv[])
 
 	check_need_password(authmethodlocal, authmethodhost);
 
+	/* set wal segment size */
+	if (str_wal_segment_size == NULL || !strlen(str_wal_segment_size))
+		wal_segment_size = DEFAULT_XLOG_SEG_SIZE;
+	else
+	{
+		char	   *endptr;
+
+		/* check that the argument is a number */
+		wal_segment_size = strtol(str_wal_segment_size, &endptr, 10);
+
+		/* verify that wal segment size is valid */
+		if (*endptr != '\0' ||
+			!IsValidXLogSegSize(wal_segment_size * 1024 * 1024))
+		{
+			fprintf(stderr,
+					_("%s: --wal-segsize must be a power of two between 1 and 1024\n"),
+					progname);
+			exit(1);
+		}
+
+		/* convert to bytes */
+		wal_segment_size = wal_segment_size * 1024 * 1024;
+	}
+
 	get_restricted_token(progname);
 
 	setup_pgdata();
diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/pg_basebackup.c
index 79c95fd..6886e35 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -2398,6 +2398,10 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	/* determine remote server's xlog segment size */
+	if (!RetrieveXLogSegSize(conn))
+		disconnect_and_exit(1);
+
 	/* Create pg_wal symlink, if required */
 	if (strcmp(xlog_dir, "") != 0)
 	{
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/pg_receivewal.c
index 318e626..442d5bc 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -255,7 +255,7 @@ FindStreamingStart(uint32 *tli)
 				disconnect_and_exit(1);
 			}
 
-			if (statbuf.st_size != XLOG_SEG_SIZE)
+			if (statbuf.st_size != XLogSegSize)
 			{
 				fprintf(stderr,
 						_("%s: segment file \"%s\" has incorrect size %d, skipping\n"),
@@ -296,7 +296,7 @@ FindStreamingStart(uint32 *tli)
 			bytes_out = (buf[3] << 24) | (buf[2] << 16) |
 				(buf[1] << 8) | buf[0];
 
-			if (bytes_out != XLOG_SEG_SIZE)
+			if (bytes_out != XLogSegSize)
 			{
 				fprintf(stderr,
 						_("%s: compressed segment file \"%s\" has incorrect uncompressed size %d, skipping\n"),
@@ -665,6 +665,10 @@ main(int argc, char **argv)
 	if (!RunIdentifySystem(conn, NULL, NULL, NULL, &db_name))
 		disconnect_and_exit(1);
 
+	/* determine remote server's xlog segment size */
+	if (!RetrieveXLogSegSize(conn))
+		disconnect_and_exit(1);
+
 	/*
 	 * Check that there is a database associated with connection, none should
 	 * be defined in this context.
diff --git a/src/bin/pg_basebackup/receivelog.c b/src/bin/pg_basebackup/receivelog.c
index 4885f31..fd3ce0a 100644
--- a/src/bin/pg_basebackup/receivelog.c
+++ b/src/bin/pg_basebackup/receivelog.c
@@ -203,7 +203,7 @@ close_walfile(StreamCtl *stream, XLogRecPtr pos)
 
 	if (stream->partial_suffix)
 	{
-		if (currpos == XLOG_SEG_SIZE)
+		if (currpos == XLogSegSize)
 			r = stream->walmethod->close(walfile, CLOSE_NORMAL);
 		else
 		{
@@ -231,7 +231,7 @@ close_walfile(StreamCtl *stream, XLogRecPtr pos)
 	 * new node. This is in line with walreceiver.c always doing a
 	 * XLogArchiveForceDone() after a complete segment.
 	 */
-	if (currpos == XLOG_SEG_SIZE && stream->mark_done)
+	if (currpos == XLogSegSize && stream->mark_done)
 	{
 		/* writes error message if failed */
 		if (!mark_file_as_archived(stream, current_walfile_name))
@@ -1149,10 +1149,10 @@ ProcessXLogDataMsg(PGconn *conn, StreamCtl *stream, char *copybuf, int len,
 
 		/*
 		 * If crossing a WAL boundary, only write up until we reach
-		 * XLOG_SEG_SIZE.
+		 * XLogSegSize.
 		 */
-		if (xlogoff + bytes_left > XLOG_SEG_SIZE)
-			bytes_to_write = XLOG_SEG_SIZE - xlogoff;
+		if (xlogoff + bytes_left > XLogSegSize)
+			bytes_to_write = XLogSegSize - xlogoff;
 		else
 			bytes_to_write = bytes_left;
 
diff --git a/src/bin/pg_basebackup/streamutil.c b/src/bin/pg_basebackup/streamutil.c
index 9d40744..3806b59 100644
--- a/src/bin/pg_basebackup/streamutil.c
+++ b/src/bin/pg_basebackup/streamutil.c
@@ -25,12 +25,18 @@
 #include "receivelog.h"
 #include "streamutil.h"
 
+#include "access/xlog_internal.h"
 #include "pqexpbuffer.h"
 #include "common/fe_memutils.h"
 #include "datatype/timestamp.h"
 
 #define ERRCODE_DUPLICATE_OBJECT  "42710"
 
+int			XLogSegSize;
+
+/* SHOW command for replication connection was introduced in version 10 */
+#define MINIMUM_VERSION_FOR_SHOW_CMD 100000
+
 const char *progname;
 char	   *connection_string = NULL;
 char	   *dbhost = NULL;
@@ -232,6 +238,76 @@ GetConnection(void)
 }
 
 /*
+ * From version 10, explicitly set XLogSegSize using SHOW wal_segment_size
+ * since ControlFile is not accessible here.
+ */
+bool
+RetrieveXLogSegSize(PGconn *conn)
+{
+	PGresult   *res;
+	char		xlog_unit[3];
+	int			xlog_val,
+				multiplier = 1;
+
+	/* check connection existence */
+	Assert(conn != NULL);
+
+	/* for previous versions set the default xlog seg size */
+	if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_SHOW_CMD)
+	{
+		XLogSegSize = DEFAULT_XLOG_SEG_SIZE;
+		return true;
+	}
+
+	res = PQexec(conn, "SHOW wal_segment_size");
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		fprintf(stderr, _("%s: could not send replication command \"%s\": %s\n"),
+				progname, "SHOW wal_segment_size", PQerrorMessage(conn));
+
+		PQclear(res);
+		return false;
+	}
+	if (PQntuples(res) != 1 || PQnfields(res) < 1)
+	{
+		fprintf(stderr,
+				_("%s: could not fetch WAL segment size: got %d rows and %d fields, expected %d rows and %d or more fields\n"),
+				progname, PQntuples(res), PQnfields(res), 1, 1);
+
+		PQclear(res);
+		return false;
+	}
+
+	/* fetch xlog value and unit from the result */
+	if (sscanf(PQgetvalue(res, 0, 0), "%d%s", &xlog_val, xlog_unit) != 2)
+	{
+		fprintf(stderr, _("%s: WAL segment size could not be parsed\n"),
+				progname);
+		return false;
+	}
+
+	/* set the multiplier based on unit to convert XLogSegSize to bytes */
+	if (strcmp(xlog_unit, "MB") == 0)
+		multiplier = 1024 * 1024;
+	else if (strcmp(xlog_unit, "GB") == 0)
+		multiplier = 1024 * 1024 * 1024;
+
+	/* convert and set XLogSegSize */
+	XLogSegSize = xlog_val * multiplier;
+
+	if (!IsValidXLogSegSize(XLogSegSize))
+	{
+		fprintf(stderr,
+				_("%s: WAL segment size must be a power of two between 1MB and 1GB, but the remote server reported a value of %d bytes\n"),
+				progname, XLogSegSize);
+		return false;
+	}
+
+	PQclear(res);
+	return true;
+}
+
+/*
  * Run IDENTIFY_SYSTEM through a given connection and give back to caller
  * some result information if requested:
  * - System identifier
diff --git a/src/bin/pg_basebackup/streamutil.h b/src/bin/pg_basebackup/streamutil.h
index 6f68786..6fb85ba 100644
--- a/src/bin/pg_basebackup/streamutil.h
+++ b/src/bin/pg_basebackup/streamutil.h
@@ -39,6 +39,7 @@ extern bool RunIdentifySystem(PGconn *conn, char **sysid,
 				  TimeLineID *starttli,
 				  XLogRecPtr *startpos,
 				  char **db_name);
+extern bool RetrieveXLogSegSize(PGconn *conn);
 extern TimestampTz feGetCurrentTimestamp(void);
 extern void feTimestampDifference(TimestampTz start_time, TimestampTz stop_time,
 					  long *secs, int *microsecs);
diff --git a/src/bin/pg_controldata/pg_controldata.c b/src/bin/pg_controldata/pg_controldata.c
index 2ea8931..9c7ea0e 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -26,6 +26,7 @@
 #include "common/controldata_utils.h"
 #include "pg_getopt.h"
 
+int			XLogSegSize;
 
 static void
 usage(const char *progname)
@@ -164,6 +165,14 @@ main(int argc, char *argv[])
 				 "Either the file is corrupt, or it has a different layout than this program\n"
 				 "is expecting.  The results below are untrustworthy.\n\n"));
 
+	/* set XLogSegSize */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
+	if (!IsValidXLogSegSize(XLogSegSize))
+		fprintf(stderr,
+				_("WARNING: WAL segment size specified, %d bytes, is not a power of two between 1MB and 1GB. The file is corrupt and the results below are untrustworthy."),
+				XLogSegSize);
+
 	/*
 	 * This slightly-chintzy coding will work as long as the control file
 	 * timestamps are within the range of time_t; that should be the case in
diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c
index ac67831..319170e 100644
--- a/src/bin/pg_resetwal/pg_resetwal.c
+++ b/src/bin/pg_resetwal/pg_resetwal.c
@@ -56,6 +56,7 @@
 #include "storage/large_object.h"
 #include "pg_getopt.h"
 
+int	XLogSegSize;
 
 static ControlFileData ControlFile; /* pg_control values */
 static XLogSegNo newXlogSegNo;	/* new XLOG segment # */
@@ -94,6 +95,7 @@ main(int argc, char *argv[])
 	char	   *endptr;
 	char	   *endptr2;
 	char	   *DataDir = NULL;
+	char	   *log_fname = NULL;
 	int			fd;
 
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_resetwal"));
@@ -265,7 +267,12 @@ main(int argc, char *argv[])
 					fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
 					exit(1);
 				}
-				XLogFromFileName(optarg, &minXlogTli, &minXlogSegNo);
+
+				/*
+				 * XLogFromFileName requires XLogSegSize which is not yet
+				 * set. Hence XLog details are set later on.
+				 */
+				log_fname = pg_strdup(optarg);
 				break;
 
 			default:
@@ -350,6 +357,9 @@ main(int argc, char *argv[])
 	if (!ReadControlFile())
 		GuessControlValues();
 
+	if (log_fname != NULL)
+		XLogFromFileName(log_fname, &minXlogTli, &minXlogSegNo);
+
 	/*
 	 * Also look at existing segment files to set up newXlogSegNo
 	 */
@@ -573,18 +583,26 @@ ReadControlFile(void)
 					offsetof(ControlFileData, crc));
 		FIN_CRC32C(crc);
 
-		if (EQ_CRC32C(crc, ((ControlFileData *) buffer)->crc))
+		if (!EQ_CRC32C(crc, ((ControlFileData *) buffer)->crc))
 		{
-			/* Valid data... */
-			memcpy(&ControlFile, buffer, sizeof(ControlFile));
-			return true;
+			/* We will use the data but treat it as guessed. */
+			fprintf(stderr, _("%s: pg_control exists but has invalid CRC; proceed with caution\n"),
+					progname);
+			guessed = true;
 		}
 
-		fprintf(stderr, _("%s: pg_control exists but has invalid CRC; proceed with caution\n"),
-				progname);
-		/* We will use the data anyway, but treat it as guessed. */
 		memcpy(&ControlFile, buffer, sizeof(ControlFile));
-		guessed = true;
+		XLogSegSize = ControlFile.xlog_seg_size;
+
+		/* return false if XLogSegSize is not valid */
+		if (!IsValidXLogSegSize(XLogSegSize))
+		{
+			fprintf(stderr,
+					_("%s: WAL segment size must be a power of two between 1MB and 1GB; ignoring control file specifying %d bytes\n"),
+					progname, XLogSegSize);
+			return false;
+		}
+
 		return true;
 	}
 
@@ -660,7 +678,7 @@ GuessControlValues(void)
 	ControlFile.blcksz = BLCKSZ;
 	ControlFile.relseg_size = RELSEG_SIZE;
 	ControlFile.xlog_blcksz = XLOG_BLCKSZ;
-	ControlFile.xlog_seg_size = XLOG_SEG_SIZE;
+	ControlFile.xlog_seg_size = DEFAULT_XLOG_SEG_SIZE;
 	ControlFile.nameDataLen = NAMEDATALEN;
 	ControlFile.indexMaxKeys = INDEX_MAX_KEYS;
 	ControlFile.toast_max_chunk_size = TOAST_MAX_CHUNK_SIZE;
diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c
index 4bd1a75..53883a5 100644
--- a/src/bin/pg_rewind/pg_rewind.c
+++ b/src/bin/pg_rewind/pg_rewind.c
@@ -44,6 +44,7 @@ static ControlFileData ControlFile_target;
 static ControlFileData ControlFile_source;
 
 const char *progname;
+int			XLogSegSize;
 
 /* Configuration options */
 char	   *datadir_target = NULL;
@@ -631,6 +632,12 @@ digestControlFile(ControlFileData *ControlFile, char *src, size_t size)
 
 	memcpy(ControlFile, src, sizeof(ControlFileData));
 
+	/* set and validate XLogSegSize */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
+	if (!IsValidXLogSegSize(XLogSegSize))
+		pg_fatal("WAL segment size must be a power of two between 1MB and 1GB, but the control file specifies %d bytes\n", XLogSegSize);
+
 	/* Additional checks on control file */
 	checkControlFile(ControlFile);
 }
diff --git a/src/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index c607b53..08548ea 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -64,7 +64,7 @@ static const char *progname;
 
 static int	secs_per_test = 5;
 static int	needs_unlink = 0;
-static char full_buf[XLOG_SEG_SIZE],
+static char full_buf[DEFAULT_XLOG_SEG_SIZE],
 		   *buf,
 		   *filename = FSYNC_FILENAME;
 static struct timeval start_t,
@@ -209,7 +209,7 @@ prepare_buf(void)
 	int			ops;
 
 	/* write random data into buffer */
-	for (ops = 0; ops < XLOG_SEG_SIZE; ops++)
+	for (ops = 0; ops < DEFAULT_XLOG_SEG_SIZE; ops++)
 		full_buf[ops] = random();
 
 	buf = (char *) TYPEALIGN(XLOG_BLCKSZ, full_buf);
@@ -226,7 +226,7 @@ test_open(void)
 	if ((tmpfile = open(filename, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR)) == -1)
 		die("could not open output file");
 	needs_unlink = 1;
-	if (write(tmpfile, full_buf, XLOG_SEG_SIZE) != XLOG_SEG_SIZE)
+	if (write(tmpfile, full_buf, DEFAULT_XLOG_SEG_SIZE) != DEFAULT_XLOG_SEG_SIZE)
 		die("write failed");
 
 	/* fsync now so that dirty buffers don't skew later tests */
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index e1fa4bb..b9819b7 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -22,10 +22,13 @@
 #include "common/fe_memutils.h"
 #include "getopt_long.h"
 #include "rmgrdesc.h"
+#include "sys/stat.h"
 
 
 static const char *progname;
 
+int			XLogSegSize;
+
 typedef struct XLogDumpPrivate
 {
 	TimeLineID	timeline;
@@ -144,77 +147,168 @@ split_path(const char *path, char **dir, char **fname)
 }
 
 /*
- * Try to find the file in several places:
- * if directory == NULL:
- *	 fname
- *	 XLOGDIR / fname
- *	 $PGDATA / XLOGDIR / fname
- * else
- *	 directory / fname
- *	 directory / XLOGDIR / fname
+ * Open the file in the valid target directory.
  *
  * return a read only fd
  */
 static int
-fuzzy_open_file(const char *directory, const char *fname)
+open_file_in_directory(const char *directory, const char *fname)
 {
 	int			fd = -1;
 	char		fpath[MAXPGPATH];
 
-	if (directory == NULL)
+	Assert(directory != NULL);
+
+	snprintf(fpath, MAXPGPATH, "%s/%s", directory, fname);
+	fd = open(fpath, O_RDONLY | PG_BINARY, 0);
+
+	if (fd < 0 && errno != ENOENT)
+		fatal_error("could not open file \"%s\": %s",
+					fname, strerror(errno));
+	return fd;
+}
+
+/*
+ * Try to find fname in the given directory. Returns true if it is found,
+ * false otherwise. If fname is NULL, search the complete directory for any
+ * file with a valid WAL file name. If file is successfully opened, set the
+ * XLogSegSize.
+ */
+static bool
+search_directory(char *directory, char *fname)
+{
+	int			fd = -1;
+	DIR		   *xldir;
+
+	/* open file if valid filename is provided */
+	if (fname != NULL)
+		fd = open_file_in_directory(directory, fname);
+
+	/*
+	 * A valid file name is not passed so search the complete directory.  If
+	 * we find any file whose name is like a valid WAL file name then try to
+	 * open it.  If we can not open it then bail out.
+	 */
+	else if ((xldir = opendir(directory)) != NULL)
+	{
+		struct dirent *xlde;
+
+		while ((xlde = readdir(xldir)) != NULL)
+		{
+			if (IsXLogFileName(xlde->d_name))
+			{
+				fd = open_file_in_directory(directory, xlde->d_name);
+				fname = xlde->d_name;
+				break;
+			}
+		}
+
+		closedir(xldir);
+	}
+
+	/* set XLogSegSize if file is successfully opened */
+	if (fd >= 0)
+	{
+		char	   *buf = (char *) malloc(XLOG_BLCKSZ);
+
+		if (read(fd, buf, XLOG_BLCKSZ) == XLOG_BLCKSZ)
+		{
+			XLogPageHeader hdr = (XLogPageHeader) buf;
+			XLogLongPageHeader longhdr = (XLogLongPageHeader) hdr;
+
+			XLogSegSize = longhdr->xlp_seg_size;
+
+			if (!IsValidXLogSegSize(XLogSegSize))
+				fatal_error("WAL segment size must be a power of two between 1MB and 1GB, but the WAL file \"%s\" header specifies %d bytes",
+							fname, XLogSegSize);
+		}
+		else
+		{
+			if (errno != 0)
+				fatal_error("could not read file \"%s\": %s",
+							fname, strerror(errno));
+			else
+				fatal_error("not enough data in file \"%s\"", fname);
+		}
+		free(buf);
+		close(fd);
+		return true;
+	}
+
+	return false;
+}
+
+/*
+ * Identify the target directory and set XLogSegSize.
+ *
+ * Try to find the file in several places:
+ * if directory != NULL:
+ *	 directory /
+ *	 directory / XLOGDIR /
+ * else
+ *	 .
+ *	 XLOGDIR /
+ *	 $PGDATA / XLOGDIR /
+ *
+ * Set the valid target directory in private->inpath.
+ */
+static void
+identify_target_directory(XLogDumpPrivate *private, char *directory,
+						  char *fname)
+{
+	char		fpath[MAXPGPATH];
+
+	if (directory != NULL)
+	{
+		if (search_directory(directory, fname))
+		{
+			private->inpath = strdup(directory);
+			return;
+		}
+
+		/* directory / XLOGDIR */
+		snprintf(fpath, MAXPGPATH, "%s/%s", directory, XLOGDIR);
+		if (search_directory(fpath, fname))
+		{
+			private->inpath = strdup(fpath);
+			return;
+		}
+	}
+	else
 	{
 		const char *datadir;
 
-		/* fname */
-		fd = open(fname, O_RDONLY | PG_BINARY, 0);
-		if (fd < 0 && errno != ENOENT)
-			return -1;
-		else if (fd >= 0)
-			return fd;
-
-		/* XLOGDIR / fname */
-		snprintf(fpath, MAXPGPATH, "%s/%s",
-				 XLOGDIR, fname);
-		fd = open(fpath, O_RDONLY | PG_BINARY, 0);
-		if (fd < 0 && errno != ENOENT)
-			return -1;
-		else if (fd >= 0)
-			return fd;
+		/* current directory */
+		if (search_directory(".", fname))
+		{
+			private->inpath = strdup(".");
+			return;
+		}
+		/* XLOGDIR */
+		if (search_directory(XLOGDIR, fname))
+		{
+			private->inpath = strdup(XLOGDIR);
+			return;
+		}
 
 		datadir = getenv("PGDATA");
-		/* $PGDATA / XLOGDIR / fname */
+		/* $PGDATA / XLOGDIR */
 		if (datadir != NULL)
 		{
-			snprintf(fpath, MAXPGPATH, "%s/%s/%s",
-					 datadir, XLOGDIR, fname);
-			fd = open(fpath, O_RDONLY | PG_BINARY, 0);
-			if (fd < 0 && errno != ENOENT)
-				return -1;
-			else if (fd >= 0)
-				return fd;
+			snprintf(fpath, MAXPGPATH, "%s/%s", datadir, XLOGDIR);
+			if (search_directory(fpath, fname))
+			{
+				private->inpath = strdup(fpath);
+				return;
+			}
 		}
 	}
+
+	/* could not locate WAL file */
+	if (fname)
+		fatal_error("could not locate WAL file \"%s\"", fname);
 	else
-	{
-		/* directory / fname */
-		snprintf(fpath, MAXPGPATH, "%s/%s",
-				 directory, fname);
-		fd = open(fpath, O_RDONLY | PG_BINARY, 0);
-		if (fd < 0 && errno != ENOENT)
-			return -1;
-		else if (fd >= 0)
-			return fd;
-
-		/* directory / XLOGDIR / fname */
-		snprintf(fpath, MAXPGPATH, "%s/%s/%s",
-				 directory, XLOGDIR, fname);
-		fd = open(fpath, O_RDONLY | PG_BINARY, 0);
-		if (fd < 0 && errno != ENOENT)
-			return -1;
-		else if (fd >= 0)
-			return fd;
-	}
-	return -1;
+		fatal_error("could not find any WAL file");
 }
 
 /*
@@ -267,7 +361,7 @@ XLogDumpXLogRead(const char *directory, TimeLineID timeline_id,
 			 */
 			for (tries = 0; tries < 10; tries++)
 			{
-				sendFile = fuzzy_open_file(directory, fname);
+				sendFile = open_file_in_directory(directory, fname);
 				if (sendFile >= 0)
 					break;
 				if (errno == ENOENT)
@@ -935,7 +1029,8 @@ main(int argc, char **argv)
 							private.inpath, strerror(errno));
 		}
 
-		fd = fuzzy_open_file(private.inpath, fname);
+		identify_target_directory(&private, private.inpath, fname);
+		fd = open_file_in_directory(private.inpath, fname);
 		if (fd < 0)
 			fatal_error("could not open file \"%s\"", fname);
 		close(fd);
@@ -968,7 +1063,7 @@ main(int argc, char **argv)
 			/* ignore directory, already have that */
 			split_path(argv[optind + 1], &directory, &fname);
 
-			fd = fuzzy_open_file(private.inpath, fname);
+			fd = open_file_in_directory(private.inpath, fname);
 			if (fd < 0)
 				fatal_error("could not open file \"%s\"", fname);
 			close(fd);
@@ -1000,6 +1095,8 @@ main(int argc, char **argv)
 			goto bad_argument;
 		}
 	}
+	else
+		identify_target_directory(&private, private.inpath, NULL);
 
 	/* we don't know what to print */
 	if (XLogRecPtrIsInvalid(private.startptr))
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 66bfb77..af5a00c 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -262,6 +262,7 @@ extern Size XLOGShmemSize(void);
 extern void XLOGShmemInit(void);
 extern void BootStrapXLOG(void);
 extern void StartupXLOG(void);
+extern void CalculateUsableBytesInSegment(void);
 extern void ShutdownXLOG(int code, Datum arg);
 extern void InitXLOGAccess(void);
 extern void CreateCheckPoint(int flags);
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 2a01b03..f2084ca 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -89,11 +89,27 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
  * The XLOG is split into WAL segments (physical files) of the size indicated
  * by XLOG_SEG_SIZE.
  */
-#define XLogSegSize		((uint32) XLOG_SEG_SIZE)
-#define XLogSegmentsPerXLogId	(UINT64CONST(0x100000000) / XLOG_SEG_SIZE)
+
+extern int	XLogSegSize;
+
+/* default number of min and max wal segments */
+#define DEFAULT_MIN_WAL_SEGS 5
+#define DEFAULT_MAX_WAL_SEGS 64
+
+/* XLogSegSize can range from 1MB to 1GB */
+#define XLogSegMinSize 1024 * 1024
+#define XLogSegMaxSize 1024 * 1024 * 1024
+
+/* check that the given size is a valid XLogSegSize */
+#define IsPowerOf2(x) (((x) & ((x)-1)) == 0)
+#define IsValidXLogSegSize(size) \
+	 (IsPowerOf2(size) && \
+	 ((size) >= XLogSegMinSize && (size) <= XLogSegMaxSize))
+
+#define XLogSegmentsPerXLogId	(UINT64CONST(0x100000000) / XLogSegSize)
 
 #define XLogSegNoOffsetToRecPtr(segno, offset, dest) \
-		(dest) = (segno) * XLOG_SEG_SIZE + (offset)
+		(dest) = (segno) * (XLogSegSize) + (offset)
 
 #define XLogSegmentOffset(xlogptr)	\
 	((xlogptr) & (XLogSegSize - 1))
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index dcb7a1a..54dd462 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -899,13 +899,6 @@
    */
 #undef XLOG_BLCKSZ
 
-/* XLOG_SEG_SIZE is the size of a single WAL file. This must be a power of 2
-   and larger than XLOG_BLCKSZ (preferably, a great deal larger than
-   XLOG_BLCKSZ). Changing XLOG_SEG_SIZE requires an initdb. */
-#undef XLOG_SEG_SIZE
-
-
-
 /* Number of bits in a file offset, on hosts where this is settable. */
 #undef _FILE_OFFSET_BITS
 
diff --git a/src/include/pg_config_manual.h b/src/include/pg_config_manual.h
index f3b3529..477e7e1 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -14,6 +14,12 @@
  */
 
 /*
+ * This is default value for wal_segment_size to be used at intidb when run
+ * without --walsegsize option.
+ */
+#define DEFAULT_XLOG_SEG_SIZE	(16*1024*1024)
+
+/*
  * Maximum length for identifiers (e.g. table names, column names,
  * function names).  Names actually are limited to one less byte than this,
  * because the length must include a trailing zero byte.
diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h
index c1870d2..1612d67 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -219,6 +219,7 @@ typedef enum
 #define GUC_UNIT_BLOCKS			0x2000	/* value is in blocks */
 #define GUC_UNIT_XBLOCKS		0x3000	/* value is in xlog blocks */
 #define GUC_UNIT_MB				0x4000	/* value is in megabytes */
+#define GUC_UNIT_BYT			0x8000	/* value is in bytes */
 #define GUC_UNIT_MEMORY			0xF000	/* mask for size-related units */
 
 #define GUC_UNIT_MS			   0x10000	/* value is in milliseconds */
diff --git a/src/tools/msvc/Solution.pm b/src/tools/msvc/Solution.pm
index 01e5846..d5e3649 100644
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -179,8 +179,6 @@ s{PG_VERSION_STR "[^"]+"}{PG_VERSION_STR "PostgreSQL $self->{strver}$extraver, c
 		  1024, "\n";
 		print $o "#define XLOG_BLCKSZ ",
 		  1024 * $self->{options}->{wal_blocksize}, "\n";
-		print $o "#define XLOG_SEG_SIZE (", $self->{options}->{wal_segsize},
-		  " * 1024 * 1024)\n";
 
 		if ($self->{options}->{float4byval})
 		{