Distinguish XLOG_FPI records generated for hint-bit updates.

Add a new XLOG_FPI_FOR_HINT record type, and use that for full-page images
generated for hint bit updates, when checksums are enabled. The new record
type is replayed exactly the same as XLOG_FPI, but allows them to be tallied
separately e.g. in pg_xlogdump.

1 files changed, 11 insertions, 7 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 2059bbeda4a..8e712b793f3 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8545,7 +8545,8 @@ xlog_redo(XLogReaderState *record)
 	XLogRecPtr	lsn = record->EndRecPtr;
 
 	/* in XLOG rmgr, backup blocks are only used by XLOG_FPI records */
-	Assert(!XLogRecHasAnyBlockRefs(record) || info == XLOG_FPI);
+	Assert(info == XLOG_FPI || info == XLOG_FPI_FOR_HINT ||
+		   !XLogRecHasAnyBlockRefs(record));
 
 	if (info == XLOG_NEXTOID)
 	{
@@ -8730,7 +8731,7 @@ xlog_redo(XLogReaderState *record)
 	{
 		/* nothing to do here */
 	}
-	else if (info == XLOG_FPI)
+	else if (info == XLOG_FPI || info == XLOG_FPI_FOR_HINT)
 	{
 		Buffer		buffer;
 
@@ -8739,12 +8740,15 @@ xlog_redo(XLogReaderState *record)
 		 * block. The block reference must include a full-page image -
 		 * otherwise there would be no point in this record.
 		 *
-		 * Since the only change in these backup block are hint bits, there
-		 * are no recovery conflicts generated.
+		 * No recovery conflicts are generated by these generic records - if a
+		 * resource manager needs to generate conflicts, it has to define a
+		 * separate WAL record type and redo routine.
 		 *
-		 * This also means there is no corresponding API call for this, so an
-		 * smgr implementation has no need to implement anything. Which means
-		 * nothing is needed in md.c etc
+		 * XLOG_FPI_FOR_HINT records are generated when a page needs to be
+		 * WAL- logged because of a hint bit update. They are only generated
+		 * when checksums are enabled. There is no difference in handling
+		 * XLOG_FPI and XLOG_FPI_FOR_HINT records, they use a different info
+		 * code just to distinguish them for statistics purposes.
 		 */
 		if (XLogReadBufferForRedo(record, 0, &buffer) != BLK_RESTORED)
 			elog(ERROR, "unexpected XLogReadBufferForRedo result when restoring backup block");