Fix buffer pin leak in heap update redo routine.

In a heap update, if the old and new tuple were on different pages, and the
new page no longer existed (because it was subsequently truncated away by
vacuum), heap_xlog_update forgot to release the pin on the old buffer. This
bug was introduced by the "Fix multiple problems in WAL replay" patch,
commit 3bbf668de9f1bc172371681e80a4e769b6d014c8 (on master branch).

With full_page_writes=off, this triggered an "incorrect local pin count"
error later in replay, if the old page was vacuumed.

This fixes bug #7969, reported by Yunong Xiao. Backpatch to 9.0, like the
commit that introduced this bug.

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index fe563188876b01ffcbd63b2fd9a546071c8372cc..9498cbb8a5132582ca09ef072c7b8f1eb02f85ce 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -6824,7 +6824,11 @@ newt:;
                                                                 ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                                                 false);
                if (!BufferIsValid(nbuffer))
+               {
+                       if (BufferIsValid(obuffer))
+                               UnlockReleaseBuffer(obuffer);
                        return;
+               }
                page = (Page) BufferGetPage(nbuffer);
 
                if (lsn <= PageGetLSN(page))    /* changes are applied */