initdb-walsegsize-v2_WIP.patch

diff --git a/configure b/configure
index 9a83f19..1b43e8c 100755
--- a/configure
+++ b/configure
@@ -816,7 +816,6 @@ enable_tap_tests
 with_blocksize
 with_segsize
 with_wal_blocksize
-with_wal_segsize
 with_CC
 enable_depend
 enable_cassert
@@ -1508,8 +1507,6 @@ 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-tcl              build Tcl modules (PL/Tcl)
   --with-tclconfig=DIR    tclConfig.sh is in DIR
@@ -3674,54 +3671,6 @@ 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) ;;
-  *) as_fn_error $? "Invalid WAL segment size. Allowed values are 1,2,4,8,16,32,64." "$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 52e4e78..4d6437c 100644
--- a/configure.in
+++ b/configure.in
@@ -344,33 +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 ${wal_segsize} in
-  1) ;;
-  2) ;;
-  4) ;;
-  8) ;;
- 16) ;;
- 32) ;;
- 64) ;;
-  *) AC_MSG_ERROR([Invalid WAL segment size. Allowed values are 1,2,4,8,16,32,64.])
-esac
-AC_MSG_RESULT([${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 e4136f9..269e6ec 100644
--- a/contrib/pg_standby/pg_standby.c
+++ b/contrib/pg_standby/pg_standby.c
@@ -36,6 +36,8 @@
 
 const char *progname;
 
+uint32		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
@@ -177,15 +179,27 @@ CustomizableNextWALFileReady(void)
 	{
 		/*
 		 * If it's a backup file, return immediately. If it's a regular file
-		 * return only if it's the right size already.
+		 * check and verify the size
 		 */
 		if (IsBackupHistoryFileName(nextWALFileName))
 		{
 			nextWALFileType = XLOG_BACKUP_LABEL;
 			return true;
 		}
-		else if (stat_buf.st_size == XLOG_SEG_SIZE)
+		else
 		{
+
+			if (!IsValidXLogSegSize(stat_buf.st_size))
+			{
+				fprintf(stderr,
+						_("%s: file size is invalid %d \n"),
+						progname, (int) stat_buf.st_size);
+
+				exit(0);
+			}
+
+			XLogSegSize = (int) stat_buf.st_size;
+
 #ifdef WIN32
 
 			/*
@@ -200,26 +214,11 @@ CustomizableNextWALFileReady(void)
 			nextWALFileType = XLOG_DATA;
 			return true;
 		}
-
-		/*
-		 * If still too small, wait until it is the correct size
-		 */
-		if (stat_buf.st_size > XLOG_SEG_SIZE)
-		{
-			if (debug)
-			{
-				fprintf(stderr, "file size greater than expected\n");
-				fflush(stderr);
-			}
-			exit(3);
-		}
 	}
 
 	return false;
 }
 
-#define MaxSegmentsPerLogFile ( 0xFFFFFFFF / XLOG_SEG_SIZE )
-
 static void
 CustomizableCleanupPriorWALFiles(void)
 {
@@ -315,6 +314,7 @@ SetWALFileNameForCleanup(void)
 	uint32		log_diff = 0,
 				seg_diff = 0;
 	bool		cleanup = false;
+	int			MaxSegmentsPerLogFile = (0xFFFFFFFF / XLOG_SEG_SIZE);
 
 	if (restartWALFileName)
 	{
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index 4431ed7..09ab77f 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1053,20 +1053,6 @@ 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 64 (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/wal.sgml b/doc/src/sgml/wal.sgml
index 346aa76..7f95863 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -752,7 +752,7 @@
    <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
+   by altering the <option>--with-wal-segsize</> initdb 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
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2f5d603..6bd5964 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -84,6 +84,7 @@ extern uint32 bootstrap_data_checksum_version;
 
 
 /* User-settable parameters */
+int			wal_segment_size = 2048;	/* 16 MB */
 int			max_wal_size = 64;	/* 1 GB */
 int			min_wal_size = 5;	/* 80 MB */
 int			wal_keep_segments = 0;
@@ -106,6 +107,24 @@ int			wal_retrieve_retry_interval = 5000;
 bool		XLOG_DEBUG = false;
 #endif
 
+uint32		XLogSegSize;
+
+/*
+ * These variables are set in assign_wal_segment_size
+ *
+ * WalModMask: It is an AND mask for XLogSegSize to allow for faster modulo
+ *		operations using it.
+ *
+ * WalShiftBit: It is an shift bit for XLogSegSize to allow for faster
+ *		division operations using it.
+ *
+ * UsableBytesInSegment: It is the number of bytes in a WAL segment usable for
+ *		WAL data.
+ */
+uint32		WalModMask;
+static int	UsableBytesInSegment;
+static int	WalShiftBit;
+
 /*
  * 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,
@@ -719,10 +738,9 @@ 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))
 
 /*
  * Private, possibly out-of-date copy of shared LogwrtResult.
@@ -957,6 +975,7 @@ XLogInsertRecord(XLogRecData *rdata,
 	if (!XLogInsertAllowed())
 		elog(ERROR, "cannot make new WAL entries during recovery");
 
+
 	/*----------
 	 *
 	 * We have now done all the preparatory work we can without holding a
@@ -1120,7 +1139,7 @@ XLogInsertRecord(XLogRecData *rdata,
 			EndPos = StartPos + SizeOfXLogRecord;
 			if (StartPos / XLOG_BLCKSZ != EndPos / XLOG_BLCKSZ)
 			{
-				if (EndPos % XLOG_SEG_SIZE == EndPos % XLOG_BLCKSZ)
+				if ((EndPos & WalModMask) == EndPos % XLOG_BLCKSZ)
 					EndPos += SizeOfXLogLongPHD;
 				else
 					EndPos += SizeOfXLogShortPHD;
@@ -1279,7 +1298,7 @@ ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos, XLogRecPtr *PrevPtr)
 	startbytepos = Insert->CurrBytePos;
 
 	ptr = XLogBytePosToEndRecPtr(startbytepos);
-	if (ptr % XLOG_SEG_SIZE == 0)
+	if ((ptr & WalModMask) == 0)
 	{
 		SpinLockRelease(&Insert->insertpos_lck);
 		*EndPos = *StartPos = ptr;
@@ -1292,7 +1311,7 @@ ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos, XLogRecPtr *PrevPtr)
 	*StartPos = XLogBytePosToRecPtr(startbytepos);
 	*EndPos = XLogBytePosToEndRecPtr(endbytepos);
 
-	segleft = XLOG_SEG_SIZE - ((*EndPos) % XLOG_SEG_SIZE);
+	segleft = XLOG_SEG_SIZE - ((*EndPos) & WalModMask);
 	if (segleft != XLOG_SEG_SIZE)
 	{
 		/* consume the rest of the segment */
@@ -1306,7 +1325,7 @@ ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos, XLogRecPtr *PrevPtr)
 
 	*PrevPtr = XLogBytePosToRecPtr(prevbytepos);
 
-	Assert((*EndPos) % XLOG_SEG_SIZE == 0);
+	Assert(((*EndPos) & WalModMask) == 0);
 	Assert(XLogRecPtrToBytePos(*EndPos) == endbytepos);
 	Assert(XLogRecPtrToBytePos(*StartPos) == startbytepos);
 	Assert(XLogRecPtrToBytePos(*PrevPtr) == prevbytepos);
@@ -1376,7 +1395,7 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
 			pagehdr->xlp_info |= XLP_FIRST_IS_CONTRECORD;
 
 			/* skip over the page header */
-			if (CurrPos % XLogSegSize == 0)
+			if ((CurrPos & WalModMask) == 0)
 			{
 				CurrPos += SizeOfXLogLongPHD;
 				currpos += SizeOfXLogLongPHD;
@@ -1407,7 +1426,7 @@ CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
 	 * allocated and zeroed in the WAL buffers so that when the caller (or
 	 * someone else) does XLogWrite(), it can really write out all the zeros.
 	 */
-	if (isLogSwitch && CurrPos % XLOG_SEG_SIZE != 0)
+	if (isLogSwitch && (CurrPos & WalModMask) != 0)
 	{
 		/* An xlog-switch record doesn't contain any data besides the header */
 		Assert(write_len == SizeOfXLogRecord);
@@ -1416,7 +1435,7 @@ 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.
 		 */
-		Assert(EndPos % XLogSegSize == 0);
+		Assert((EndPos & WalModMask) == 0);
 
 		/* Use up all the remaining space on the first page */
 		CurrPos += freespace;
@@ -1741,10 +1760,10 @@ GetXLogBuffer(XLogRecPtr ptr)
 		 * the page header.
 		 */
 		if (ptr % XLOG_BLCKSZ == SizeOfXLogShortPHD &&
-			ptr % XLOG_SEG_SIZE > XLOG_BLCKSZ)
+			(ptr & WalModMask) > XLOG_BLCKSZ)
 			initializedUpto = ptr - SizeOfXLogShortPHD;
 		else if (ptr % XLOG_BLCKSZ == SizeOfXLogLongPHD &&
-				 ptr % XLOG_SEG_SIZE < XLOG_BLCKSZ)
+				 (ptr & WalModMask) < XLOG_BLCKSZ)
 			initializedUpto = ptr - SizeOfXLogLongPHD;
 		else
 			initializedUpto = ptr;
@@ -1794,6 +1813,7 @@ XLogBytePosToRecPtr(uint64 bytepos)
 	uint32		seg_offset;
 	XLogRecPtr	result;
 
+
 	fullsegs = bytepos / UsableBytesInSegment;
 	bytesleft = bytepos % UsableBytesInSegment;
 
@@ -1878,7 +1898,7 @@ XLogRecPtrToBytePos(XLogRecPtr ptr)
 
 	XLByteToSeg(ptr, fullsegs);
 
-	fullpages = (ptr % XLOG_SEG_SIZE) / XLOG_BLCKSZ;
+	fullpages = (ptr & WalModMask) / XLOG_BLCKSZ;
 	offset = ptr % XLOG_BLCKSZ;
 
 	if (fullpages == 0)
@@ -2043,7 +2063,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 		/*
 		 * If first page of an XLOG segment file, make it a long header.
 		 */
-		if ((NewPage->xlp_pageaddr % XLogSegSize) == 0)
+		if ((NewPage->xlp_pageaddr & WalModMask) == 0)
 		{
 			XLogLongPageHeader NewLongPage = (XLogLongPageHeader) NewPage;
 
@@ -2095,6 +2115,7 @@ CalculateCheckpointSegments(void)
 	 *	  number of segments consumed between checkpoints.
 	 *-------
 	 */
+
 	target = (double) max_wal_size / (2.0 + CheckPointCompletionTarget);
 
 	/* round down */
@@ -2105,9 +2126,58 @@ CalculateCheckpointSegments(void)
 }
 
 void
+assign_wal_segment_size(int newval, void *extra)
+{
+	/*
+	 * During system initialization, XLogSegSize is not set so we use
+	 * DEFAULT_XLOG_SEG_SIZE instead.
+	 */
+	int	WalSegSize = (XLogSegSize == 0) ? DEFAULT_XLOG_SEG_SIZE : XLOG_SEG_SIZE;
+
+	wal_segment_size = newval;
+	UsableBytesInSegment = (wal_segment_size * UsableBytesInPage) -
+						   (SizeOfXLogLongPHD - SizeOfXLogShortPHD);
+	WalModMask = WalSegSize - 1;
+
+	/* Set the WalShiftBit */
+	WalShiftBit = 0;
+	while (WalSegSize > 1)
+	{
+		WalSegSize = WalSegSize >> 1;
+		WalShiftBit++;
+	}
+}
+
+void
+assign_min_wal_size(int newval, void *extra)
+{
+	/*
+	 * During system initialization, XLogSegSize is not set so we use
+	 * DEFAULT_XLOG_SEG_SIZE instead.
+	 *
+	 * min_wal_size is in kB and XLogSegSize is in bytes and so it is
+	 * converted to kB for the calculation.
+	 */
+	int	WalSegSize = (XLogSegSize == 0) ? (DEFAULT_XLOG_SEG_SIZE / 1024) :
+										  (XLOG_SEG_SIZE / 1024);
+
+	min_wal_size = newval / WalSegSize;
+}
+
+void
 assign_max_wal_size(int newval, void *extra)
 {
-	max_wal_size = newval;
+	/*
+	 * During system initialization, XLogSegSize is not set so we use
+	 * DEFAULT_XLOG_SEG_SIZE instead.
+	 *
+	 * max_wal_size is in kB and XLogSegSize is in bytes and so it is
+	 * converted to bytes for the calculation.
+	 */
+	int	WalSegSize = (XLogSegSize == 0) ? (DEFAULT_XLOG_SEG_SIZE / 1024) :
+										  (XLOG_SEG_SIZE / 1024);
+
+	max_wal_size = newval / WalSegSize;
 	CalculateCheckpointSegments();
 }
 
@@ -2135,8 +2205,8 @@ 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 + min_wal_size - 1;
-	maxSegNo = PriorRedoPtr / XLOG_SEG_SIZE + max_wal_size - 1;
+	minSegNo = (PriorRedoPtr >> WalShiftBit) + min_wal_size - 1;
+	maxSegNo = (PriorRedoPtr >> WalShiftBit) + max_wal_size - 1;
 
 	/*
 	 * Between those limits, recycle enough segments to get us through to the
@@ -2297,7 +2367,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
 		{
 			/* first of group */
 			startidx = curridx;
-			startoffset = (LogwrtResult.Write - XLOG_BLCKSZ) % XLogSegSize;
+			startoffset = (LogwrtResult.Write - XLOG_BLCKSZ) & WalModMask;
 		}
 		npages++;
 
@@ -3606,7 +3676,7 @@ PreallocXlogFiles(XLogRecPtr endptr)
 	bool		use_existent;
 
 	XLByteToPrevSeg(endptr, _logSegNo);
-	if ((endptr - 1) % XLogSegSize >= (uint32) (0.75 * XLogSegSize))
+	if (((endptr - 1) & WalModMask) >= (uint32) (0.75 * XLogSegSize))
 	{
 		_logSegNo++;
 		use_existent = true;
@@ -4060,7 +4130,7 @@ ReadRecord(XLogReaderState *xlogreader, XLogRecPtr RecPtr, int emode,
 			int32		offset;
 
 			XLByteToSeg(xlogreader->latestPagePtr, segno);
-			offset = xlogreader->latestPagePtr % XLogSegSize;
+			offset = xlogreader->latestPagePtr & WalModMask;
 			XLogFileName(fname, xlogreader->readPageTLI, segno);
 			ereport(emode_for_corrupt_record(emode,
 											 RecPtr ? RecPtr : EndRecPtr),
@@ -4329,6 +4399,8 @@ ReadControlFile(void)
 {
 	pg_crc32c	crc;
 	int			fd;
+	uint32		wal_segsz;
+	static char wal_segsz_str[20];
 
 	/*
 	 * Read data...
@@ -4429,13 +4501,6 @@ 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"),
@@ -4512,10 +4577,15 @@ ReadControlFile(void)
 				  " but the server was compiled without USE_FLOAT8_BYVAL."),
 				 errhint("It looks like you need to recompile or initdb.")));
 #endif
+	XLogSegSize = ControlFile->xlog_seg_size;
 
 	/* Make the initdb settings visible as GUC variables, too */
 	SetConfigOption("data_checksums", DataChecksumsEnabled() ? "yes" : "no",
 					PGC_INTERNAL, PGC_S_OVERRIDE);
+	wal_segsz = XLOG_SEG_SIZE / XLOG_BLCKSZ;
+	snprintf(wal_segsz_str, sizeof(wal_segsz_str), "%d", wal_segsz);
+	SetConfigOption("wal_segment_size", wal_segsz_str, PGC_INTERNAL,
+					PGC_S_OVERRIDE);
 }
 
 void
@@ -4619,10 +4689,11 @@ XLOGChooseNumBuffers(void)
 	int			xbuffers;
 
 	xbuffers = NBuffers / 32;
-	if (xbuffers > XLOG_SEG_SIZE / XLOG_BLCKSZ)
-		xbuffers = XLOG_SEG_SIZE / XLOG_BLCKSZ;
+	if (xbuffers > wal_segment_size)
+		xbuffers = wal_segment_size;
 	if (xbuffers < 8)
 		xbuffers = 8;
+
 	return xbuffers;
 }
 
@@ -4669,6 +4740,7 @@ XLOGShmemSize(void)
 {
 	Size		size;
 
+	char		buf[32];
 	/*
 	 * If the value of wal_buffers is -1, use the preferred auto-tune value.
 	 * This isn't an amazingly clean place to do this, but we must wait till
@@ -4677,8 +4749,18 @@ XLOGShmemSize(void)
 	 */
 	if (XLOGbuffers == -1)
 	{
-		char		buf[32];
-
+		/*
+		 * The calculation of XLOGbuffers, requires the now run-time parameter
+		 * XLogSegSize from the ControlFile. The value determined here is
+		 * required to create the shared memory segment. Hence, temporarily
+		 * allocating space and reading ControlFile here.
+		 */
+		if (!IsBootstrapProcessingMode())
+		{
+			ControlFile = palloc(sizeof(ControlFileData));
+			ReadControlFile();
+			pfree(ControlFile);
+		}
 		snprintf(buf, sizeof(buf), "%d", XLOGChooseNumBuffers());
 		SetConfigOption("wal_buffers", buf, PGC_POSTMASTER, PGC_S_OVERRIDE);
 	}
@@ -4824,6 +4906,13 @@ BootStrapXLOG(void)
 	pg_crc32c	crc;
 
 	/*
+	 * initdb passes the WAL segment size in an environment variable. We don't
+	 * bother doing any sanity checking, we already check in initdb that the
+	 * user gives a sane value.
+	 */
+	XLogSegSize = pg_atoi(getenv("XLOG_SEG_SIZE"), sizeof(uint32), 0);
+
+	/*
 	 * Select a hopefully-unique system identifier code for this installation.
 	 * We use the result of gettimeofday(), including the fractional seconds
 	 * field, as being about as unique as we can easily get.  (Think not to
@@ -5366,7 +5455,7 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
 		 * avoid emplacing a bogus file.
 		 */
 		XLogFileCopy(endLogSegNo, endTLI, endLogSegNo,
-					 endOfLog % XLOG_SEG_SIZE);
+					 (endOfLog & WalModMask));
 	}
 	else
 	{
@@ -7298,7 +7387,7 @@ StartupXLOG(void)
 		XLogRecPtr	pageBeginPtr;
 
 		pageBeginPtr = EndOfLog - (EndOfLog % XLOG_BLCKSZ);
-		Assert(readOff == pageBeginPtr % XLogSegSize);
+		Assert(readOff == (pageBeginPtr & WalModMask));
 
 		firstIdx = XLogRecPtrToBufIdx(EndOfLog);
 
@@ -7447,7 +7536,7 @@ StartupXLOG(void)
 		 * restored from the archive to begin with, it's expected to have a
 		 * .done file).
 		 */
-		if (EndOfLog % XLOG_SEG_SIZE != 0 && XLogArchivingActive())
+		if ((EndOfLog & WalModMask) != 0 && XLogArchivingActive())
 		{
 			char		origfname[MAXFNAMELEN];
 			XLogSegNo	endLogSegNo;
@@ -7967,6 +8056,9 @@ InitXLOGAccess(void)
 	ThisTimeLineID = XLogCtl->ThisTimeLineID;
 	Assert(ThisTimeLineID != 0 || IsBootstrapProcessingMode());
 
+	/* Same for XLOG_SEG_SIZE */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
 	/* Use GetRedoRecPtr to copy the RedoRecPtr safely */
 	(void) GetRedoRecPtr();
 	/* Also update our copy of doPageWrites. */
@@ -8485,7 +8577,7 @@ CreateCheckPoint(int flags)
 	freespace = INSERT_FREESPACE(curInsert);
 	if (freespace == 0)
 	{
-		if (curInsert % XLogSegSize == 0)
+		if ((curInsert & WalModMask) == 0)
 			curInsert += SizeOfXLogLongPHD;
 		else
 			curInsert += SizeOfXLogShortPHD;
@@ -10739,7 +10831,7 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 	 */
 	XLByteToSeg(startpoint, _logSegNo);
 	BackupHistoryFilePath(histfilepath, ThisTimeLineID, _logSegNo,
-						  (uint32) (startpoint % XLogSegSize));
+						  (uint32) (startpoint & WalModMask));
 	fp = AllocateFile(histfilepath, "w");
 	if (!fp)
 		ereport(ERROR,
@@ -10792,7 +10884,7 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
 
 		XLByteToSeg(startpoint, _logSegNo);
 		BackupHistoryFileName(histfilename, ThisTimeLineID, _logSegNo,
-							  (uint32) (startpoint % XLogSegSize));
+							  (uint32) (startpoint & WalModMask));
 
 		seconds_before_warning = 60;
 		waits = 0;
@@ -11236,7 +11328,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	XLogSegNo targetSegNo PG_USED_FOR_ASSERTS_ONLY;
 
 	XLByteToSeg(targetPagePtr, targetSegNo);
-	targetPageOff = targetPagePtr % XLogSegSize;
+	targetPageOff = targetPagePtr & WalModMask;
 
 	/*
 	 * See if we need to switch to a new segment because the requested record
@@ -11303,7 +11395,7 @@ retry:
 		if (((targetPagePtr) / XLOG_BLCKSZ) != (receivedUpto / XLOG_BLCKSZ))
 			readLen = XLOG_BLCKSZ;
 		else
-			readLen = receivedUpto % XLogSegSize - targetPageOff;
+			readLen = (receivedUpto & WalModMask) - targetPageOff;
 	}
 	else
 		readLen = XLOG_BLCKSZ;
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 63e6552..ca47b7e 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -494,7 +494,7 @@ pg_xlogfile_name_offset(PG_FUNCTION_ARGS)
 	/*
 	 * offset
 	 */
-	xrecoff = locationpoint % XLogSegSize;
+	xrecoff = locationpoint & WalModMask;
 
 	values[1] = UInt32GetDatum(xrecoff);
 	isnull[1] = false;
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 0de2419..bf06185 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -672,7 +672,7 @@ XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
 		int			segbytes;
 		int			readbytes;
 
-		startoff = recptr % XLogSegSize;
+		startoff = recptr & WalModMask;
 
 		/* Do we need to switch to a different xlog segment? */
 		if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo))
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index fe9041f..c004e8b 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -624,7 +624,7 @@ CheckArchiveTimeout(void)
 			 * If the returned pointer points exactly to a segment boundary,
 			 * assume nothing happened.
 			 */
-			if ((switchpoint % XLogSegSize) != 0)
+			if ((switchpoint & WalModMask) != 0)
 				ereport(DEBUG1,
 						(errmsg("transaction log switch forced (archive_timeout=%d)",
 								XLogArchiveTimeout)));
diff --git a/src/backend/replication/walreceiver.c b/src/backend/replication/walreceiver.c
index 0e4a4b9..9ff2395 100644
--- a/src/backend/replication/walreceiver.c
+++ b/src/backend/replication/walreceiver.c
@@ -991,7 +991,7 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
 		}
 
 		/* Calculate the start offset of the received logs */
-		startoff = recptr % XLogSegSize;
+		startoff = (recptr & WalModMask);
 
 		if (startoff + nbytes > XLogSegSize)
 			segbytes = XLogSegSize - startoff;
diff --git a/src/backend/replication/walreceiverfuncs.c b/src/backend/replication/walreceiverfuncs.c
index df113b8..42d2da2 100644
--- a/src/backend/replication/walreceiverfuncs.c
+++ b/src/backend/replication/walreceiverfuncs.c
@@ -234,8 +234,8 @@ RequestXLogStreaming(TimeLineID tli, XLogRecPtr recptr, const char *conninfo,
 	 * being created by XLOG streaming, which might cause trouble later on if
 	 * the segment is e.g archived.
 	 */
-	if (recptr % XLogSegSize != 0)
-		recptr -= recptr % XLogSegSize;
+	if ((recptr & WalModMask) != 0)
+		recptr -= (recptr & WalModMask);
 
 	SpinLockAcquire(&walrcv->mutex);
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index f3082c3..8535b4e 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -2047,7 +2047,7 @@ retry:
 		int			segbytes;
 		int			readbytes;
 
-		startoff = recptr % XLogSegSize;
+		startoff = (recptr & WalModMask);
 
 		if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo))
 		{
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5f43b1e..1dd15de 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -31,6 +31,7 @@
 #include "access/transam.h"
 #include "access/twophase.h"
 #include "access/xact.h"
+#include "access/xlog_internal.h"
 #include "catalog/namespace.h"
 #include "commands/async.h"
 #include "commands/prepare.h"
@@ -510,7 +511,6 @@ 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;
 
@@ -708,9 +708,6 @@ 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\".");
 
@@ -731,11 +728,6 @@ static const unit_conversion memory_unit_conversion_table[] =
 	{"MB", GUC_UNIT_XBLOCKS, 1024 / (XLOG_BLCKSZ / 1024)},
 	{"kB", GUC_UNIT_XBLOCKS, -(XLOG_BLCKSZ / 1024)},
 
-	{"TB", GUC_UNIT_XSEGS, (1024 * 1024 * 1024) / (XLOG_SEG_SIZE / 1024)},
-	{"GB", GUC_UNIT_XSEGS, (1024 * 1024) / (XLOG_SEG_SIZE / 1024)},
-	{"MB", GUC_UNIT_XSEGS, -(XLOG_SEG_SIZE / (1024 * 1024))},
-	{"kB", GUC_UNIT_XSEGS, -(XLOG_SEG_SIZE / 1024)},
-
 	{""}						/* end of table marker */
 };
 
@@ -2223,21 +2215,21 @@ static struct config_int ConfigureNamesInt[] =
 		{"min_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Sets the minimum size to shrink the WAL to."),
 			NULL,
-			GUC_UNIT_XSEGS
+			GUC_UNIT_KB
 		},
 		&min_wal_size,
-		5, 2, INT_MAX,
-		NULL, NULL, NULL
+		5 * 16 * 1024, 2, INT_MAX,
+		NULL, assign_min_wal_size, NULL
 	},
 
 	{
 		{"max_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
 			gettext_noop("Sets the WAL size that triggers a checkpoint."),
 			NULL,
-			GUC_UNIT_XSEGS
+			GUC_UNIT_KB
 		},
 		&max_wal_size,
-		64, 2, INT_MAX,
+		64 * 16 * 1024, 2, INT_MAX,
 		NULL, assign_max_wal_size, NULL
 	},
 
@@ -2592,10 +2584,10 @@ static struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_XBLOCKS | 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),
-		NULL, NULL, NULL
+		DEFAULT_XLOG_SEG_SIZE / XLOG_BLCKSZ,
+		16,
+		INT_MAX,
+		NULL, assign_wal_segment_size, NULL
 	},
 
 	{
@@ -8041,11 +8033,6 @@ GetConfigOptionByNum(int varnum, const char **values, bool *noshow)
 				snprintf(buffer, sizeof(buffer), "%dkB", XLOG_BLCKSZ / 1024);
 				values[2] = pstrdup(buffer);
 				break;
-			case GUC_UNIT_XSEGS:
-				snprintf(buffer, sizeof(buffer), "%dMB",
-						 XLOG_SEG_SIZE / (1024 * 1024));
-				values[2] = pstrdup(buffer);
-				break;
 			case GUC_UNIT_MS:
 				values[2] = "ms";
 				break;
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 443c2ee..b8c8ec0 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -53,6 +53,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <locale.h>
+#include <math.h>
 #include <signal.h>
 #include <time.h>
 
@@ -60,6 +61,7 @@
 #include "sys/mman.h"
 #endif
 
+#include "access/xlog_internal.h"
 #include "catalog/catalog.h"
 #include "catalog/pg_authid.h"
 #include "common/file_utils.h"
@@ -140,6 +142,8 @@ 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 */
@@ -1338,6 +1342,9 @@ bootstrap_template1(void)
 	snprintf(cmd, sizeof(cmd), "LC_CTYPE=%s", lc_ctype);
 	putenv(pg_strdup(cmd));
 
+	snprintf(cmd, sizeof(cmd), "XLOG_SEG_SIZE=%d", wal_segment_size);
+	putenv(pg_strdup(cmd));
+
 	unsetenv("LC_ALL");
 
 	/* Also ensure backend isn't confused by this environment var: */
@@ -2256,6 +2263,7 @@ 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, --xlogdir=XLOGDIR     location for the transaction 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"));
@@ -2942,6 +2950,7 @@ main(int argc, char *argv[])
 		{"no-sync", no_argument, NULL, 'N'},
 		{"sync-only", no_argument, NULL, 'S'},
 		{"xlogdir", required_argument, NULL, 'X'},
+		{"wal-segsize", required_argument, NULL, 'Z'},
 		{"data-checksums", no_argument, NULL, 'k'},
 		{NULL, 0, NULL, 0}
 	};
@@ -3075,6 +3084,9 @@ main(int argc, char *argv[])
 			case 'X':
 				xlog_dir = pg_strdup(optarg);
 				break;
+			case 'Z':
+				str_wal_segment_size = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
@@ -3137,6 +3149,23 @@ main(int argc, char *argv[])
 
 	check_need_password(authmethodlocal, authmethodhost);
 
+	if (str_wal_segment_size == NULL || !strlen(str_wal_segment_size))
+		wal_segment_size = DEFAULT_XLOG_SEG_SIZE;
+	else
+	{
+		wal_segment_size = atoi(str_wal_segment_size);
+
+		/* Check if wal_segment_size is valid */
+		if (!IsValidXLogSegSize(wal_segment_size * 1024 * 1024))
+		{
+			fprintf(stderr, _("%s: Invalid WAL segment size %d\n"), progname, wal_segment_size);
+			exit(1);
+		}
+
+		/* Convert wal_segment_size 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 ce1fe3b..6674dee 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -2380,6 +2380,9 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	if (!SetXLogSegSize(conn))
+		disconnect_and_exit(1);
+
 	/* Create transaction log symlink, if required */
 	if (strcmp(xlog_dir, "") != 0)
 	{
diff --git a/src/bin/pg_basebackup/receivelog.h b/src/bin/pg_basebackup/receivelog.h
index 42e93ac..9265dc0 100644
--- a/src/bin/pg_basebackup/receivelog.h
+++ b/src/bin/pg_basebackup/receivelog.h
@@ -16,6 +16,7 @@
 #include "walmethods.h"
 
 #include "access/xlogdefs.h"
+#include "access/xlog_internal.h"
 
 /*
  * Called before trying to read more data or when a segment is
@@ -54,4 +55,5 @@ extern bool CheckServerVersionForStreaming(PGconn *conn);
 extern bool ReceiveXlogStream(PGconn *conn,
 				  StreamCtl *stream);
 
+uint32		XLogSegSize;
 #endif   /* RECEIVELOG_H */
diff --git a/src/bin/pg_basebackup/streamutil.c b/src/bin/pg_basebackup/streamutil.c
index 31290d3..87efc3c 100644
--- a/src/bin/pg_basebackup/streamutil.c
+++ b/src/bin/pg_basebackup/streamutil.c
@@ -238,6 +238,59 @@ GetConnection(void)
 }
 
 /*
+ * Run the SHOW_WAL_SEGMENT_SIZE command to set the XLogSegSize
+ */
+bool
+SetXLogSegSize(PGconn *conn)
+{
+	PGresult   *res;
+	char	   *tmp_result;
+	char		xlog_unit[2];
+	int			xlog_val,
+				multiplier = 1;
+
+	/* Check connection existence */
+	Assert(conn != NULL);
+
+	res = PQexec(conn, "SHOW wal_segment_size");
+	if (PQresultStatus(res) != PGRES_TUPLES_OK)
+	{
+		fprintf(stderr, _("%s: could not send replication command \"%s\": %s"),
+				progname, "SHOW wal_segment_size", PQerrorMessage(conn));
+
+		PQclear(res);
+		return false;
+	}
+	if (PQntuples(res) != 1 || PQnfields(res) < 1)
+	{
+		fprintf(stderr,
+				_("%s: could not identify system: 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;
+	}
+
+	/* wal_segment_size ranges from 1MB to 1GB */
+	tmp_result = pg_strdup(PQgetvalue(res, 0, 0));
+
+	/* Fetch the xlog value and unit from the result */
+	sscanf(tmp_result, "%d%s", &xlog_val, xlog_unit);
+
+	/* XLogSegSize should be in bytes, set the multiplier based on unit */
+	if (strcmp(xlog_unit, "MB") == 0)
+		multiplier = 1024 * 1024;
+	else if (strcmp(xlog_unit, "GB") == 0)
+		multiplier = 1024 * 1024 * 1024;
+
+	/* Set the XLogSegSize */
+	XLogSegSize = xlog_val * multiplier;
+
+	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 663bfac..bef750b 100644
--- a/src/bin/pg_basebackup/streamutil.h
+++ b/src/bin/pg_basebackup/streamutil.h
@@ -38,6 +38,7 @@ extern bool RunIdentifySystem(PGconn *conn, char **sysid,
 				  TimeLineID *starttli,
 				  XLogRecPtr *startpos,
 				  char **db_name);
+extern bool SetXLogSegSize(PGconn *conn);
 extern int64 feGetCurrentTimestamp(void);
 extern void feTimestampDifference(int64 start_time, int64 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 20077a6..45bd5bb 100644
--- a/src/bin/pg_controldata/pg_controldata.c
+++ b/src/bin/pg_controldata/pg_controldata.c
@@ -27,6 +27,8 @@
 #include "pg_getopt.h"
 
 
+uint32		XLogSegSize;
+
 static void
 usage(const char *progname)
 {
@@ -163,6 +165,11 @@ main(int argc, char *argv[])
 				 "is expecting.  The results below are untrustworthy.\n\n"));
 
 	/*
+	 * Read the XLOG_SEG_SIZE
+	 */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
+	/*
 	 * 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
 	 * all foreseeable circumstances, so we don't bother importing the
diff --git a/src/bin/pg_resetxlog/pg_resetxlog.c b/src/bin/pg_resetxlog/pg_resetxlog.c
index 963802e..4ceebdc 100644
--- a/src/bin/pg_resetxlog/pg_resetxlog.c
+++ b/src/bin/pg_resetxlog/pg_resetxlog.c
@@ -57,6 +57,7 @@
 #include "storage/large_object.h"
 #include "pg_getopt.h"
 
+uint32		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_resetxlog"));
@@ -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
+				 * defined. Hence XLog details are set later on.
+				 */
+				log_fname = pg_strdup(optarg);
 				break;
 
 			default:
@@ -347,6 +354,9 @@ 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
 	 */
@@ -510,6 +520,7 @@ ReadControlFile(void)
 		{
 			/* Valid data... */
 			memcpy(&ControlFile, buffer, sizeof(ControlFile));
+			XLogSegSize = ControlFile.xlog_seg_size;
 			return true;
 		}
 
@@ -517,6 +528,7 @@ ReadControlFile(void)
 				progname);
 		/* We will use the data anyway, but treat it as guessed. */
 		memcpy(&ControlFile, buffer, sizeof(ControlFile));
+		XLogSegSize = ControlFile.xlog_seg_size;
 		guessed = true;
 		return true;
 	}
diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c
index 2014fee..8d0d4a5 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;
+uint32		XLogSegSize;
 
 /* Configuration options */
 char	   *datadir_target = NULL;
@@ -631,6 +632,11 @@ digestControlFile(ControlFileData *ControlFile, char *src, size_t size)
 
 	memcpy(ControlFile, src, sizeof(ControlFileData));
 
+	/*
+	 * Read the XLOG_SEG_SIZE
+	 */
+	XLogSegSize = ControlFile->xlog_seg_size;
+
 	/* 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 d65c0ab..b262ae8 100644
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -62,7 +62,7 @@ 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,
@@ -204,7 +204,7 @@ 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);
@@ -221,7 +221,7 @@ 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_xlogdump/pg_xlogdump.c b/src/bin/pg_xlogdump/pg_xlogdump.c
index 590d2ad..61e8276 100644
--- a/src/bin/pg_xlogdump/pg_xlogdump.c
+++ b/src/bin/pg_xlogdump/pg_xlogdump.c
@@ -22,9 +22,11 @@
 #include "common/fe_memutils.h"
 #include "getopt_long.h"
 #include "rmgrdesc.h"
+#include "sys/stat.h"
 
 
 static const char *progname;
+uint32		XLogSegSize;
 
 typedef struct XLogDumpPrivate
 {
@@ -892,8 +894,10 @@ main(int argc, char **argv)
 	{
 		char	   *directory = NULL;
 		char	   *fname = NULL;
+		char		full_path[PATH_MAX];
 		int			fd;
 		XLogSegNo	segno;
+		struct stat fst;
 
 		split_path(argv[optind], &directory, &fname);
 
@@ -911,6 +915,25 @@ main(int argc, char **argv)
 			fatal_error("could not open file \"%s\"", fname);
 		close(fd);
 
+		if (private.inpath != NULL)
+			sprintf(full_path, "%s/%s", private.inpath, fname);
+		else
+			strcpy(full_path, fname);
+
+		stat(full_path, &fst);
+
+		if (!IsValidXLogSegSize(fst.st_size))
+		{
+			fprintf(stderr,
+					_("%s: file size %d is invalid \n"),
+					progname, (int) fst.st_size);
+
+			return EXIT_FAILURE;
+
+		}
+
+		XLogSegSize = (int) fst.st_size;
+
 		/* parse position from file */
 		XLogFromFileName(fname, &private.timeline, &segno);
 
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index a425572..8ee107b 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -94,6 +94,7 @@ extern PGDLLIMPORT XLogRecPtr XactLastCommitEnd;
 extern bool reachedConsistency;
 
 /* these variables are GUC parameters related to XLOG */
+extern int	wal_segment_size;
 extern int	min_wal_size;
 extern int	max_wal_size;
 extern int	wal_keep_segments;
@@ -281,7 +282,9 @@ extern void SetWalWriterSleeping(bool sleeping);
 
 extern void XLogRequestWalReceiverReply(void);
 
+extern void assign_wal_segment_size(int newval, void *extra);
 extern void assign_max_wal_size(int newval, void *extra);
+extern void assign_min_wal_size(int newval, void *extra);
 extern void assign_checkpoint_completion_target(double newval, void *extra);
 
 /*
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 8ad4d47..a2d3e89 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -89,7 +89,22 @@ 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)
+
+extern uint32 WalModMask;
+extern uint32 XLogSegSize;
+#define XLOG_SEG_SIZE XLogSegSize
+
+/* XLogSegSize can range from 1MB to 1GB */
+#define XLogSegMinSize 1024 * 1024
+#define XLogSegMaxSize 1024 * 1024 * 1024
+
+/*	Check if the given size is a valid XLogSegSize */
+#define	IsPower2(x)	((x & (x-1)) == 0)
+#define IsValidXLogSegSize(size) \
+	 ((size % (1024 * 1024) == 0) && \
+	  IsPower2(size / (1024 * 1024)) && \
+	  (size >= XLogSegMinSize && size <= XLogSegMaxSize))
+
 #define XLogSegmentsPerXLogId	(UINT64CONST(0x100000000) / XLOG_SEG_SIZE)
 
 #define XLogSegNoOffsetToRecPtr(segno, offset, dest) \
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index b9dfdd4..7a143cc 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -912,13 +912,6 @@
    */
 #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 c079071..d7d939c 100644
--- a/src/include/pg_config_manual.h
+++ b/src/include/pg_config_manual.h
@@ -14,6 +14,12 @@
  */
 
 /*
+ * This default value is used for wal_segment_size during initdb when no other
+ * value is specified with --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 7dd3780..9ff1119 100644
--- a/src/include/utils/guc.h
+++ b/src/include/utils/guc.h
@@ -218,7 +218,6 @@ typedef enum
 #define GUC_UNIT_KB				0x1000	/* value is in kilobytes */
 #define GUC_UNIT_BLOCKS			0x2000	/* value is in blocks */
 #define GUC_UNIT_XBLOCKS		0x3000	/* value is in xlog blocks */
-#define GUC_UNIT_XSEGS			0x4000	/* value is in xlog segments */
 #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 fbf4da3..920e4c0 100644
--- a/src/tools/msvc/Solution.pm
+++ b/src/tools/msvc/Solution.pm
@@ -183,7 +183,7 @@ s{PG_VERSION_STR "[^"]+"}{__STRINGIFY(x) #x\n#define __STRINGIFY2(z) __STRINGIFY
 		  1024, "\n";
 		print O "#define XLOG_BLCKSZ ",
 		  1024 * $self->{options}->{wal_blocksize}, "\n";
-		print O "#define XLOG_SEG_SIZE (", $self->{options}->{wal_segsize},
+		print O "#define DEFAULT_XLOG_SEG_SIZE (", $self->{options}->{wal_segsize},
 		  " * 1024 * 1024)\n";
 
 		if ($self->{options}->{float4byval})