Restore relmapper state early enough in parallel workers.

tglsfdc · tglsfdc · commit 126ec0bc76d0 · 2024-09-19T20:58:21.000-04:00
We need to do RestoreRelationMap before loading catalog-derived state, else the worker may end up with catalog relcache entries containing stale relfilenode data. Move up RestoreReindexState too, on the principle that that should also happen before we do much of any catalog access. I think ideally these things would happen even before InitPostgres, but there are various problems standing in the way of that, notably that the relmapper thinks "active" mappings should be discarded at transaction end. The implication of this is that InitPostgres and RestoreLibraryState will see the same catalog state as an independent backend would see, which is probably fine; at least, it's been like that all along. Per report from Justin Pryzby. There is a case to be made that this should be back-patched. But given the lack of complaints before 6e086fa and the short amount of time remaining before 17.0 wraps, I'll just put it in HEAD for now. Discussion: https://postgr.es/m/ZuoU_8EbSTE14o1U@pryzbyj2023
diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
@@ -1420,6 +1420,17 @@ ParallelWorkerMain(Datum main_arg)
 	tstatespace = shm_toc_lookup(toc, PARALLEL_KEY_TRANSACTION_STATE, false);
 	StartParallelWorkerTransaction(tstatespace);
 
+	/*
+	 * Restore relmapper and reindex state early, since these affect catalog
+	 * access.  Ideally we'd do this even before calling InitPostgres, but
+	 * that has order-of-initialization problems, and also the relmapper would
+	 * get confused during the CommitTransactionCommand call above.
+	 */
+	relmapperspace = shm_toc_lookup(toc, PARALLEL_KEY_RELMAPPER_STATE, false);
+	RestoreRelationMap(relmapperspace);
+	reindexspace = shm_toc_lookup(toc, PARALLEL_KEY_REINDEX_STATE, false);
+	RestoreReindexState(reindexspace);
+
 	/* Restore combo CID state. */
 	combocidspace = shm_toc_lookup(toc, PARALLEL_KEY_COMBO_CID, false);
 	RestoreComboCIDState(combocidspace);
@@ -1482,14 +1493,6 @@ ParallelWorkerMain(Datum main_arg)
 									   false);
 	RestorePendingSyncs(pendingsyncsspace);
 
-	/* Restore reindex state. */
-	reindexspace = shm_toc_lookup(toc, PARALLEL_KEY_REINDEX_STATE, false);
-	RestoreReindexState(reindexspace);
-
-	/* Restore relmapper state. */
-	relmapperspace = shm_toc_lookup(toc, PARALLEL_KEY_RELMAPPER_STATE, false);
-	RestoreRelationMap(relmapperspace);
-
 	/* Restore uncommitted enums. */
 	uncommittedenumsspace = shm_toc_lookup(toc, PARALLEL_KEY_UNCOMMITTEDENUMS,
 										   false);
