Get heap page max offset with buffer lock held.

On further reflection it seems better to call PageGetMaxOffsetNumber()
after acquiring a buffer lock on the page.  This shouldn't really
matter, but doing it this way is cleaner.

Follow-up to commit 42288174.

Backpatch: 12-, just like commit 42288174

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 4e25622b4a3af0bb6433344d80cdcf0db1ffc442..6bd49d0025236418cb1b1a82d9b73c46f959f672 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7042,10 +7042,10 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
            xid_horizon_prefetch_buffer(rel, &prefetch_state, 1);
 #endif
 
+           LockBuffer(buf, BUFFER_LOCK_SHARE);
+
            page = BufferGetPage(buf);
            maxoff = PageGetMaxOffsetNumber(page);
-
-           LockBuffer(buf, BUFFER_LOCK_SHARE);
        }
 
        /*