1 files changed, 39 insertions, 1 deletions

diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 5cf74e181a1..4b03577dccd 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -278,6 +278,7 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 				total_len;
 	uint32		targetRecOff;
 	uint32		pageHeaderSize;
+	bool		assembled;
 	bool		gotheader;
 	int			readOff;
 
@@ -293,6 +294,8 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 	state->errormsg_buf[0] = '\0';
 
 	ResetDecoder(state);
+	state->abortedRecPtr = InvalidXLogRecPtr;
+	state->missingContrecPtr = InvalidXLogRecPtr;
 
 	RecPtr = state->EndRecPtr;
 
@@ -319,7 +322,9 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 		randAccess = true;
 	}
 
+restart:
 	state->currRecPtr = RecPtr;
+	assembled = false;
 
 	targetPagePtr = RecPtr - (RecPtr % XLOG_BLCKSZ);
 	targetRecOff = RecPtr % XLOG_BLCKSZ;
@@ -415,6 +420,8 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 		char	   *buffer;
 		uint32		gotlen;
 
+		assembled = true;
+
 		/*
 		 * Enlarge readRecordBuf as needed.
 		 */
@@ -448,8 +455,25 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 
 			Assert(SizeOfXLogShortPHD <= readOff);
 
-			/* Check that the continuation on next page looks valid */
 			pageHeader = (XLogPageHeader) state->readBuf;
+
+			/*
+			 * If we were expecting a continuation record and got an
+			 * "overwrite contrecord" flag, that means the continuation record
+			 * was overwritten with a different record.  Restart the read by
+			 * assuming the address to read is the location where we found
+			 * this flag; but keep track of the LSN of the record we were
+			 * reading, for later verification.
+			 */
+			if (pageHeader->xlp_info & XLP_FIRST_IS_OVERWRITE_CONTRECORD)
+			{
+				state->overwrittenRecPtr = state->currRecPtr;
+				ResetDecoder(state);
+				RecPtr = targetPagePtr;
+				goto restart;
+			}
+
+			/* Check that the continuation on next page looks valid */
 			if (!(pageHeader->xlp_info & XLP_FIRST_IS_CONTRECORD))
 			{
 				report_invalid_record(state,
@@ -551,6 +575,20 @@ XLogReadRecord(XLogReaderState *state, char **errormsg)
 		return NULL;
 
 err:
+	if (assembled)
+	{
+		/*
+		 * We get here when a record that spans multiple pages needs to be
+		 * assembled, but something went wrong -- perhaps a contrecord piece
+		 * was lost.  If caller is WAL replay, it will know where the aborted
+		 * record was and where to direct followup WAL to be written, marking
+		 * the next piece with XLP_FIRST_IS_OVERWRITE_CONTRECORD, which will
+		 * in turn signal downstream WAL consumers that the broken WAL record
+		 * is to be ignored.
+		 */
+		state->abortedRecPtr = RecPtr;
+		state->missingContrecPtr = targetPagePtr;
+	}
 
 	/*
 	 * Invalidate the read state. We might read from a different source after