Get heap page max offset with buffer lock held.

petergeoghegan · petergeoghegan · commit 5f95664e1919 · 2020-12-30T17:21:39.000-08:00
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 4228817. Backpatch: 12-, just like commit 4228817
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -7084,10 +7084,10 @@ 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);
 		}
 
 		/*
