Fix parallel worker tracking of new catalog relfilenumbers.

Reunite RestorePendingSyncs() with RestoreRelationMap().  If
RelationInitPhysicalAddr() ran after RestoreRelationMap() but before
RestorePendingSyncs(), the relcache entry could cause RelationNeedsWAL()
to return true erroneously.  Trouble required commands of the current
transaction to include REINDEX or CLUSTER of a system catalog.  The
parallel leader correctly derived RelationNeedsWAL()==false from the new
relfilenumber, but the worker saw RelationNeedsWAL()==true.  Worker
MarkBufferDirtyHint() then wrote unwanted WAL.  Recovery of that
unwanted WAL could lose tuples like the system could before commit
c6b9204 introduced this tracking.
RestorePendingSyncs() and RestoreRelationMap() were adjacent till commit
126ec0b, so no back-patch for now.

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/20241019232815.c6.nmisch@google.com

Author: nmisch

src/backend/access/transam/parallel.c

@@ -1421,17 +1421,18 @@ ParallelWorkerMain(Datum main_arg)
 	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.
+	 * Restore state that affects 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.
 	 */
+	pendingsyncsspace = shm_toc_lookup(toc, PARALLEL_KEY_PENDING_SYNCS,
+									   false);
+	RestorePendingSyncs(pendingsyncsspace);
 	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);
 
@@ -1488,11 +1489,6 @@ ParallelWorkerMain(Datum main_arg)
 	SetTempNamespaceState(fps->temp_namespace_id,
 						  fps->temp_toast_namespace_id);
 
-	/* Restore pending syncs. */
-	pendingsyncsspace = shm_toc_lookup(toc, PARALLEL_KEY_PENDING_SYNCS,
-									   false);
-	RestorePendingSyncs(pendingsyncsspace);
-
 	/* Restore uncommitted enums. */
 	uncommittedenumsspace = shm_toc_lookup(toc, PARALLEL_KEY_UNCOMMITTEDENUMS,
 										   false);