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 da27903cb4c9276b1e0734e6ed43d6bd603e0f11..26c2006f23c0bbd8b969072f6bfe4ec1026b5836 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7075,10 +7075,10 @@ 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);
        }
 
        /*