From c25ed20067d21a97242a023031fcdcc232d6945c Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Mon, 5 Jun 2017 15:56:58 -0700
Subject: [PATCH] Fix record length computation in pg_waldump/xlogdump.

The current method of computing the record length (excluding the
lenght of full-page images) has been wrong since the WAL format has
been revamped in 2c03216d831160bedd72d45f712601b6f7d03f1c.  Only the
main record's length was counted, but that can be significantly too
little if there's data associated with further blocks.

Fix by computing the record length as total_lenght - fpi_length.

Reported-By: Chen Huajun
Bug: #14687
Reviewed-By: Heikki Linnakangas
Discussion: https://postgr.es/m/20170603165939.1436.58887@wrigleys.postgresql.org
Backpatch: 9.5-
---
 src/bin/pg_waldump/pg_waldump.c | 51 ++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 16 deletions(-)

diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 6bc27f4be36..2578d4b6920 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -362,6 +362,35 @@ XLogDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
 	return count;
 }
 
+/*
+ * Calculate the size of a record, split into !FPI and FPI parts.
+ */
+static void
+XLogDumpRecordLen(XLogReaderState *record, uint32 *rec_len, uint32 *fpi_len)
+{
+	int			block_id;
+
+	/*
+	 * Calculate the amount of FPI data in the record.
+	 *
+	 * XXX: We peek into xlogreader's private decoded backup blocks for the
+	 * bimg_len indicating the length of FPI data. It doesn't seem worth it to
+	 * add an accessor macro for this.
+	 */
+	*fpi_len = 0;
+	for (block_id = 0; block_id <= record->max_block_id; block_id++)
+	{
+		if (XLogRecHasBlockImage(record, block_id))
+			*fpi_len += record->blocks[block_id].bimg_len;
+	}
+
+	/*
+	 * Calculate the length of the record as the total length - the length of
+	 * all the block images.
+	 */
+	*rec_len = XLogRecGetTotalLen(record) - *fpi_len;
+}
+
 /*
  * Store per-rmgr and per-record statistics for a given record.
  */
@@ -373,26 +402,12 @@ XLogDumpCountRecord(XLogDumpConfig *config, XLogDumpStats *stats,
 	uint8		recid;
 	uint32		rec_len;
 	uint32		fpi_len;
-	int			block_id;
 
 	stats->count++;
 
 	rmid = XLogRecGetRmid(record);
-	rec_len = XLogRecGetDataLen(record) + SizeOfXLogRecord;
 
-	/*
-	 * Calculate the amount of FPI data in the record.
-	 *
-	 * XXX: We peek into xlogreader's private decoded backup blocks for the
-	 * bimg_len indicating the length of FPI data. It doesn't seem worth it to
-	 * add an accessor macro for this.
-	 */
-	fpi_len = 0;
-	for (block_id = 0; block_id <= record->max_block_id; block_id++)
-	{
-		if (XLogRecHasBlockImage(record, block_id))
-			fpi_len += record->blocks[block_id].bimg_len;
-	}
+	XLogDumpRecordLen(record, &rec_len, &fpi_len);
 
 	/* Update per-rmgr statistics */
 
@@ -422,6 +437,8 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogReaderState *record)
 {
 	const char *id;
 	const RmgrDescData *desc = &RmgrDescTable[XLogRecGetRmid(record)];
+	uint32		rec_len;
+	uint32		fpi_len;
 	RelFileNode rnode;
 	ForkNumber	forknum;
 	BlockNumber blk;
@@ -429,13 +446,15 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogReaderState *record)
 	uint8		info = XLogRecGetInfo(record);
 	XLogRecPtr	xl_prev = XLogRecGetPrev(record);
 
+	XLogDumpRecordLen(record, &rec_len, &fpi_len);
+
 	id = desc->rm_identify(info);
 	if (id == NULL)
 		id = psprintf("UNKNOWN (%x)", info & ~XLR_INFO_MASK);
 
 	printf("rmgr: %-11s len (rec/tot): %6u/%6u, tx: %10u, lsn: %X/%08X, prev %X/%08X, ",
 		   desc->rm_name,
-		   XLogRecGetDataLen(record), XLogRecGetTotalLen(record),
+		   rec_len, XLogRecGetTotalLen(record),
 		   XLogRecGetXid(record),
 		   (uint32) (record->ReadRecPtr >> 32), (uint32) record->ReadRecPtr,
 		   (uint32) (xl_prev >> 32), (uint32) xl_prev);