commit 9a57858f1103b89a5674f0d50c5fe1f756411df6
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:   Thu Feb 27 11:13:39 2014 -0300

    Fix WAL replay of locking an updated tuple
    
    We were resetting the tuple's HEAP_HOT_UPDATED flag as well as t_ctid on
    WAL replay of a tuple-lock operation, which is incorrect when the tuple
    is already updated.
    
    Back-patch to 9.3.  The clearing of both header elements was there
    previously, but since no update could be present on a tuple that was
    being locked, it was harmless.
    
    Bug reported by Peter Geoghegan and Greg Stark in
    CAM3SWZTMQiCi5PV5OWHb+bYkUcnCk=O67w0cSswPvV7XfUcU5g@mail.gmail.com and
    CAM-w4HPTOeMT4KP0OJK+mGgzgcTOtLRTvFZyvD0O4aH-7dxo3Q@mail.gmail.com
    respectively; diagnosis by Andres Freund.

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 33fc5a7..d94980b 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7721,11 +7721,19 @@ heap_xlog_lock(XLogRecPtr lsn, XLogRecord *record)
 
 	fix_infomask_from_infobits(xlrec->infobits_set, &htup->t_infomask,
 							   &htup->t_infomask2);
-	HeapTupleHeaderClearHotUpdated(htup);
+
+	/*
+	 * Clear relevant update flags, but only if the modified infomask says
+	 * there's no update.
+	 */
+	if (HEAP_XMAX_IS_LOCKED_ONLY(htup->t_infomask))
+	{
+		HeapTupleHeaderClearHotUpdated(htup);
+		/* Make sure there is no forward chain link in t_ctid */
+		htup->t_ctid = xlrec->target.tid;
+	}
 	HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
 	HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
-	/* Make sure there is no forward chain link in t_ctid */
-	htup->t_ctid = xlrec->target.tid;
 	PageSetLSN(page, lsn);
 	MarkBufferDirty(buffer);
 	UnlockReleaseBuffer(buffer);