Replace XLogRecPtr struct with a 64-bit integer.

This simplifies code that needs to do arithmetic on XLogRecPtrs.

To avoid changing on-disk format of data pages, the LSN on data pages is
still stored in the old format. That should keep pg_upgrade happy. However,
we have XLogRecPtrs embedded in the control file, and in the structs that
are sent over the replication protocol, so this changes breaks compatibility
of pg_basebackup and server. I didn't do anything about this in this patch,
per discussion on -hackers, the right thing to do would to be to change the
replication protocol to be architecture-independent, so that you could use
a newer version of pg_receivexlog, for example, against an older server
version.

1 files changed, 12 insertions, 37 deletions

diff --git a/src/include/access/xlogdefs.h b/src/include/access/xlogdefs.h
index 603854884f0..153d0de22a9 100644
--- a/src/include/access/xlogdefs.h
+++ b/src/include/access/xlogdefs.h
@@ -17,55 +17,30 @@
 /*
  * Pointer to a location in the XLOG.  These pointers are 64 bits wide,
  * because we don't want them ever to overflow.
- *
- * NOTE: xrecoff == 0 is used to indicate an invalid pointer.  This is OK
- * because we use page headers in the XLOG, so no XLOG record can start
- * right at the beginning of a file.
- *
- * NOTE: the "log file number" is somewhat misnamed, since the actual files
- * making up the XLOG are much smaller than 4Gb.  Each actual file is an
- * XLogSegSize-byte "segment" of a logical log file having the indicated
- * xlogid.	The log file number and segment number together identify a
- * physical XLOG file.	Segment number and offset within the physical file
- * are computed from xrecoff div and mod XLogSegSize.
  */
-typedef struct XLogRecPtr
-{
-	uint32		xlogid;			/* log file #, 0 based */
-	uint32		xrecoff;		/* byte offset of location in log file */
-} XLogRecPtr;
-
-#define XLogRecPtrIsInvalid(r)	((r).xrecoff == 0)
+typedef uint64 XLogRecPtr;
 
+/*
+ * Zero is used indicate an invalid pointer. Bootstrap skips the first possible
+ * WAL segment, initializing the first WAL page at XLOG_SEG_SIZE, so no XLOG
+ * record can begin at zero.
+ */
+#define InvalidXLogRecPtr	0
+#define XLogRecPtrIsInvalid(r)	((r) == InvalidXLogRecPtr)
 
 /*
  * Macros for comparing XLogRecPtrs
- *
- * Beware of passing expressions with side-effects to these macros,
- * since the arguments may be evaluated multiple times.
  */
-#define XLByteLT(a, b)		\
-			((a).xlogid < (b).xlogid || \
-			 ((a).xlogid == (b).xlogid && (a).xrecoff < (b).xrecoff))
-
-#define XLByteLE(a, b)		\
-			((a).xlogid < (b).xlogid || \
-			 ((a).xlogid == (b).xlogid && (a).xrecoff <= (b).xrecoff))
-
-#define XLByteEQ(a, b)		\
-			((a).xlogid == (b).xlogid && (a).xrecoff == (b).xrecoff)
+#define XLByteLT(a, b)		((a) < (b))
+#define XLByteLE(a, b)		((a) <= (b))
+#define XLByteEQ(a, b)		((a) == (b))
 
 
 /*
  * Macro for advancing a record pointer by the specified number of bytes.
  */
 #define XLByteAdvance(recptr, nbytes)						\
-	do {													\
-		uint32 oldxrecoff = (recptr).xrecoff;				\
-		(recptr).xrecoff += nbytes;							\
-		if ((recptr).xrecoff < oldxrecoff)					\
-			(recptr).xlogid += 1;		/* xrecoff wrapped around */	\
-	} while (0)
+		(recptr) += nbytes									\
 
 /*
  * XLogSegNo - physical log file sequence number.