Don't waste the last segment of each 4GB logical log file.

The comments claimed that wasting the last segment made it easier to do
calculations with XLogRecPtrs, because you don't have problems representing
last-byte-position-plus-1 that way. In my experience, however, it only made
things more complicated, because the there was two ways to represent the
boundary at the beginning of a logical log file: logid = n+1 and xrecoff = 0,
or as xlogid = n and xrecoff = 4GB - XLOG_SEG_SIZE. Some functions were
picky about which representation was used.

Also, use a 64-bit segment number instead of the log/seg combination, to
point to a certain WAL segment. We assume that all platforms have a working
64-bit integer type nowadays.

This is an incompatible change in WAL format, so bumping WAL version number.

1 files changed, 16 insertions, 32 deletions

diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index adf0b16e56a..bbb87d4d5cd 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -271,8 +271,7 @@ pg_xlogfile_name_offset(PG_FUNCTION_ARGS)
 	char	   *locationstr;
 	unsigned int uxlogid;
 	unsigned int uxrecoff;
-	uint32		xlogid;
-	uint32		xlogseg;
+	XLogSegNo	xlogsegno;
 	uint32		xrecoff;
 	XLogRecPtr	locationpoint;
 	char		xlogfilename[MAXFNAMELEN];
@@ -319,8 +318,8 @@ pg_xlogfile_name_offset(PG_FUNCTION_ARGS)
 	/*
 	 * xlogfilename
 	 */
-	XLByteToPrevSeg(locationpoint, xlogid, xlogseg);
-	XLogFileName(xlogfilename, ThisTimeLineID, xlogid, xlogseg);
+	XLByteToPrevSeg(locationpoint, xlogsegno);
+	XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno);
 
 	values[0] = CStringGetTextDatum(xlogfilename);
 	isnull[0] = false;
@@ -328,7 +327,7 @@ pg_xlogfile_name_offset(PG_FUNCTION_ARGS)
 	/*
 	 * offset
 	 */
-	xrecoff = locationpoint.xrecoff - xlogseg * XLogSegSize;
+	xrecoff = locationpoint.xrecoff % XLogSegSize;
 
 	values[1] = UInt32GetDatum(xrecoff);
 	isnull[1] = false;
@@ -354,8 +353,7 @@ pg_xlogfile_name(PG_FUNCTION_ARGS)
 	char	   *locationstr;
 	unsigned int uxlogid;
 	unsigned int uxrecoff;
-	uint32		xlogid;
-	uint32		xlogseg;
+	XLogSegNo	xlogsegno;
 	XLogRecPtr	locationpoint;
 	char		xlogfilename[MAXFNAMELEN];
 
@@ -378,8 +376,8 @@ pg_xlogfile_name(PG_FUNCTION_ARGS)
 	locationpoint.xlogid = uxlogid;
 	locationpoint.xrecoff = uxrecoff;
 
-	XLByteToPrevSeg(locationpoint, xlogid, xlogseg);
-	XLogFileName(xlogfilename, ThisTimeLineID, xlogid, xlogseg);
+	XLByteToPrevSeg(locationpoint, xlogsegno);
+	XLogFileName(xlogfilename, ThisTimeLineID, xlogsegno);
 
 	PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
 }
@@ -514,6 +512,8 @@ pg_xlog_location_diff(PG_FUNCTION_ARGS)
 	XLogRecPtr	loc1,
 				loc2;
 	Numeric		result;
+	uint64		bytes1,
+				bytes2;
 
 	/*
 	 * Read and parse input
@@ -533,33 +533,17 @@ pg_xlog_location_diff(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 		   errmsg("could not parse transaction log location \"%s\"", str2)));
 
-	/*
-	 * Sanity check
-	 */
-	if (loc1.xrecoff > XLogFileSize)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("xrecoff \"%X\" is out of valid range, 0..%X", loc1.xrecoff, XLogFileSize)));
-	if (loc2.xrecoff > XLogFileSize)
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("xrecoff \"%X\" is out of valid range, 0..%X", loc2.xrecoff, XLogFileSize)));
+	bytes1 = (((uint64)loc1.xlogid) << 32L) + loc1.xrecoff;
+	bytes2 = (((uint64)loc2.xlogid) << 32L) + loc2.xrecoff;
 
 	/*
-	 * result = XLogFileSize * (xlogid1 - xlogid2) + xrecoff1 - xrecoff2
+	 * result = bytes1 - bytes2.
+	 *
+	 * XXX: this won't handle values higher than 2^63 correctly.
 	 */
 	result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
-	   DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc1.xlogid)),
-	 DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc2.xlogid))));
-	result = DatumGetNumeric(DirectFunctionCall2(numeric_mul,
-	  DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) XLogFileSize)),
-												 NumericGetDatum(result)));
-	result = DatumGetNumeric(DirectFunctionCall2(numeric_add,
-												 NumericGetDatum(result),
-	DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc1.xrecoff))));
-	result = DatumGetNumeric(DirectFunctionCall2(numeric_sub,
-												 NumericGetDatum(result),
-	DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) loc2.xrecoff))));
+	   DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) bytes1)),
+	   DirectFunctionCall1(int8_numeric, Int64GetDatum((int64) bytes2))));
 
 	PG_RETURN_NUMERIC(result);
 }