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.

3 files changed, 61 insertions, 77 deletions

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index df5f232eeea..b58191085b4 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -267,12 +267,10 @@ extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
 extern void XLogFlush(XLogRecPtr RecPtr);
 extern bool XLogBackgroundFlush(void);
 extern bool XLogNeedsFlush(XLogRecPtr RecPtr);
-extern int XLogFileInit(uint32 log, uint32 seg,
-			 bool *use_existent, bool use_lock);
-extern int	XLogFileOpen(uint32 log, uint32 seg);
+extern int XLogFileInit(XLogSegNo segno, bool *use_existent, bool use_lock);
+extern int	XLogFileOpen(XLogSegNo segno);
 
-
-extern void XLogGetLastRemoved(uint32 *log, uint32 *seg);
+extern void XLogGetLastRemoved(XLogSegNo *segno);
 extern void XLogSetAsyncXactLSN(XLogRecPtr record);
 
 extern void RestoreBkpBlocks(XLogRecPtr lsn, XLogRecord *record, bool cleanup);
@@ -280,7 +278,7 @@ extern void RestoreBkpBlocks(XLogRecPtr lsn, XLogRecord *record, bool cleanup);
 extern void xlog_redo(XLogRecPtr lsn, XLogRecord *record);
 extern void xlog_desc(StringInfo buf, uint8 xl_info, char *rec);
 
-extern void issue_xlog_fsync(int fd, uint32 log, uint32 seg);
+extern void issue_xlog_fsync(int fd, XLogSegNo segno);
 
 extern bool RecoveryInProgress(void);
 extern bool HotStandbyActive(void);
@@ -294,6 +292,7 @@ extern bool RecoveryIsPaused(void);
 extern void SetRecoveryPause(bool recoveryPause);
 extern TimestampTz GetLatestXTime(void);
 extern TimestampTz GetCurrentChunkReplayStartTime(void);
+extern char *XLogFileNameP(TimeLineID tli, XLogSegNo segno);
 
 extern void UpdateControlFile(void);
 extern uint64 GetSystemIdentifier(void);
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h
index 29a0310dcf9..50b4c2f3782 100644
--- a/src/include/access/xlog_internal.h
+++ b/src/include/access/xlog_internal.h
@@ -71,7 +71,7 @@ typedef struct XLogContRecord
 /*
  * Each page of XLOG file has a header like this:
  */
-#define XLOG_PAGE_MAGIC 0xD071	/* can be used as WAL version indicator */
+#define XLOG_PAGE_MAGIC 0xD072	/* can be used as WAL version indicator */
 
 typedef struct XLogPageHeaderData
 {
@@ -115,55 +115,27 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
 	(((hdr)->xlp_info & XLP_LONG_HEADER) ? SizeOfXLogLongPHD : SizeOfXLogShortPHD)
 
 /*
- * We break each logical log file (xlogid value) into segment files of the
- * size indicated by XLOG_SEG_SIZE.  One possible segment at the end of each
- * log file is wasted, to ensure that we don't have problems representing
- * last-byte-position-plus-1.
+ * The XLOG is split into WAL segments (physical files) of the size indicated
+ * by XLOG_SEG_SIZE.
  */
 #define XLogSegSize		((uint32) XLOG_SEG_SIZE)
-#define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize)
-#define XLogFileSize	(XLogSegsPerFile * XLogSegSize)
+#define XLogSegmentsPerXLogId	(0x100000000L / XLOG_SEG_SIZE)
 
+#define XLogSegNoOffsetToRecPtr(segno, offset, dest) \
+	do {	\
+		(dest).xlogid = (segno) / XLogSegmentsPerXLogId;				\
+		(dest).xrecoff = ((segno) % XLogSegmentsPerXLogId) * XLOG_SEG_SIZE + (offset); \
+	} while (0)
 
 /*
  * Macros for manipulating XLOG pointers
  */
 
-/* Increment an xlogid/segment pair */
-#define NextLogSeg(logId, logSeg)	\
-	do { \
-		if ((logSeg) >= XLogSegsPerFile-1) \
-		{ \
-			(logId)++; \
-			(logSeg) = 0; \
-		} \
-		else \
-			(logSeg)++; \
-	} while (0)
-
-/* Decrement an xlogid/segment pair (assume it's not 0,0) */
-#define PrevLogSeg(logId, logSeg)	\
-	do { \
-		if (logSeg) \
-			(logSeg)--; \
-		else \
-		{ \
-			(logId)--; \
-			(logSeg) = XLogSegsPerFile-1; \
-		} \
-	} while (0)
-
 /* Align a record pointer to next page */
 #define NextLogPage(recptr) \
 	do {	\
 		if ((recptr).xrecoff % XLOG_BLCKSZ != 0)	\
-			(recptr).xrecoff += \
-				(XLOG_BLCKSZ - (recptr).xrecoff % XLOG_BLCKSZ); \
-		if ((recptr).xrecoff >= XLogFileSize) \
-		{	\
-			((recptr).xlogid)++;	\
-			(recptr).xrecoff = 0; \
-		}	\
+			XLByteAdvance(recptr, (XLOG_BLCKSZ - (recptr).xrecoff % XLOG_BLCKSZ)); \
 	} while (0)
 
 /*
@@ -175,14 +147,11 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
  * for example.  (We can assume xrecoff is not zero, since no valid recptr
  * can have that.)
  */
-#define XLByteToSeg(xlrp, logId, logSeg)	\
-	( logId = (xlrp).xlogid, \
-	  logSeg = (xlrp).xrecoff / XLogSegSize \
-	)
-#define XLByteToPrevSeg(xlrp, logId, logSeg)	\
-	( logId = (xlrp).xlogid, \
-	  logSeg = ((xlrp).xrecoff - 1) / XLogSegSize \
-	)
+#define XLByteToSeg(xlrp, logSegNo)	\
+	logSegNo = ((uint64) (xlrp).xlogid * XLogSegmentsPerXLogId) + (xlrp).xrecoff / XLogSegSize
+
+#define XLByteToPrevSeg(xlrp, logSegNo)	\
+	logSegNo = ((uint64) (xlrp).xlogid * XLogSegmentsPerXLogId) + ((xlrp).xrecoff - 1) / XLogSegSize
 
 /*
  * Is an XLogRecPtr within a particular XLOG segment?
@@ -190,13 +159,16 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
  * For XLByteInSeg, do the computation at face value.  For XLByteInPrevSeg,
  * a boundary byte is taken to be in the previous segment.
  */
-#define XLByteInSeg(xlrp, logId, logSeg)	\
-	((xlrp).xlogid == (logId) && \
-	 (xlrp).xrecoff / XLogSegSize == (logSeg))
+#define XLByteInSeg(xlrp, logSegNo)	\
+	(((xlrp).xlogid) == (logSegNo) / XLogSegmentsPerXLogId &&			\
+	 ((xlrp).xrecoff / XLogSegSize) == (logSegNo) % XLogSegmentsPerXLogId)
 
-#define XLByteInPrevSeg(xlrp, logId, logSeg)	\
-	((xlrp).xlogid == (logId) && \
-	 ((xlrp).xrecoff - 1) / XLogSegSize == (logSeg))
+#define XLByteInPrevSeg(xlrp, logSegNo)	\
+	(((xlrp).xrecoff == 0) ?											\
+		(((xlrp).xlogid - 1) == (logSegNo) / XLogSegmentsPerXLogId && \
+		 ((uint32) 0xffffffff) / XLogSegSize == (logSegNo) % XLogSegmentsPerXLogId) : \
+		((xlrp).xlogid) == (logSegNo) / XLogSegmentsPerXLogId &&	\
+		 (((xlrp).xrecoff - 1) / XLogSegSize) == (logSegNo) % XLogSegmentsPerXLogId)
 
 /* Check if an xrecoff value is in a plausible range */
 #define XRecOffIsValid(xrecoff) \
@@ -215,14 +187,23 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
  */
 #define MAXFNAMELEN		64
 
-#define XLogFileName(fname, tli, log, seg)	\
-	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli, log, seg)
-
-#define XLogFromFileName(fname, tli, log, seg)	\
-	sscanf(fname, "%08X%08X%08X", tli, log, seg)
+#define XLogFileName(fname, tli, logSegNo)	\
+	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X", tli,		\
+			 (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \
+			 (uint32) ((logSegNo) % XLogSegmentsPerXLogId))
+
+#define XLogFromFileName(fname, tli, logSegNo)	\
+	do {												\
+		uint32 log;										\
+		uint32 seg;										\
+		sscanf(fname, "%08X%08X%08X", tli, &log, &seg);	\
+		*logSegNo = (uint64) log * XLogSegmentsPerXLogId + seg;	\
+	} while (0)
 
-#define XLogFilePath(path, tli, log, seg)	\
-	snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X", tli, log, seg)
+#define XLogFilePath(path, tli, logSegNo)	\
+	snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X", tli,				\
+			 (uint32) ((logSegNo) / XLogSegmentsPerXLogId),				\
+			 (uint32) ((logSegNo) % XLogSegmentsPerXLogId))
 
 #define TLHistoryFileName(fname, tli)	\
 	snprintf(fname, MAXFNAMELEN, "%08X.history", tli)
@@ -233,11 +214,15 @@ typedef XLogLongPageHeaderData *XLogLongPageHeader;
 #define StatusFilePath(path, xlog, suffix)	\
 	snprintf(path, MAXPGPATH, XLOGDIR "/archive_status/%s%s", xlog, suffix)
 
-#define BackupHistoryFileName(fname, tli, log, seg, offset) \
-	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X.%08X.backup", tli, log, seg, offset)
+#define BackupHistoryFileName(fname, tli, logSegNo, offset) \
+	snprintf(fname, MAXFNAMELEN, "%08X%08X%08X.%08X.backup", tli, \
+			 (uint32) ((logSegNo) / XLogSegmentsPerXLogId),		  \
+			 (uint32) ((logSegNo) % XLogSegmentsPerXLogId), offset)
 
-#define BackupHistoryFilePath(path, tli, log, seg, offset)	\
-	snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X.%08X.backup", tli, log, seg, offset)
+#define BackupHistoryFilePath(path, tli, logSegNo, offset)	\
+	snprintf(path, MAXPGPATH, XLOGDIR "/%08X%08X%08X.%08X.backup", tli, \
+			 (uint32) ((logSegNo) / XLogSegmentsPerXLogId), \
+			 (uint32) ((logSegNo) % XLogSegmentsPerXLogId), offset)
 
 
 /*
diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index 5e6d7e600bd..603854884f0 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -61,16 +61,16 @@ typedef struct XLogRecPtr
  */
 #define XLByteAdvance(recptr, nbytes)						\
 	do {													\
-		if (recptr.xrecoff + nbytes >= XLogFileSize)		\
-		{													\
-			recptr.xlogid += 1;								\
-			recptr.xrecoff									\
-				= recptr.xrecoff + nbytes - XLogFileSize;	\
-		}													\
-		else												\
-			recptr.xrecoff += nbytes;						\
+		uint32 oldxrecoff = (recptr).xrecoff;				\
+		(recptr).xrecoff += nbytes;							\
+		if ((recptr).xrecoff < oldxrecoff)					\
+			(recptr).xlogid += 1;		/* xrecoff wrapped around */	\
 	} while (0)
 
+/*
+ * XLogSegNo - physical log file sequence number.
+ */
+typedef uint64 XLogSegNo;
 
 /*
  * TimeLineID (TLI) - identifies different database histories to prevent