Fix determination of broken LSN in OVERWRITTEN_CONTRECORD

alvherre · alvherre · commit ef41c3fd6c86 · 2021-11-26T11:14:27.000-03:00
In commit ff9f111 I mixed up inconsistent definitions of the LSN of the first record in a page, when the previous record ends exactly at the page boundary. The correct LSN is adjusted to skip the WAL page header; I failed to use that when setting XLogReaderState->overwrittenRecPtr, so at WAL replay time VerifyOverwriteContrecord would refuse to let replay continue past that record. Backpatch to 10. 9.6 also contains this bug, but it's no longer being maintained. Discussion: https://postgr.es/m/45597.1637694259@sss.pgh.pa.us
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
@@ -465,7 +465,7 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 			 */
 			if (pageHeader->xlp_info & XLP_FIRST_IS_OVERWRITE_CONTRECORD)
 			{
-				state->overwrittenRecPtr = state->currRecPtr;
+				state->overwrittenRecPtr = RecPtr;
 				ResetDecoder(state);
 				RecPtr = targetPagePtr;
 				goto restart;

Original file line number	Diff line number	Diff line change
`@@ -465,7 +465,7 @@ XLogReadRecord(XLogReaderState state, char *errormsg)`
`465`	`465`	`*/`
`466`	`466`	`if (pageHeader->xlp_info & XLP_FIRST_IS_OVERWRITE_CONTRECORD)`
`467`	`467`	`{`
`468`		`- state->overwrittenRecPtr = state->currRecPtr;`
	`468`	`+ state->overwrittenRecPtr = RecPtr;`
`469`	`469`	`ResetDecoder(state);`
`470`	`470`	`RecPtr = targetPagePtr;`
`471`	`471`	`goto restart;`