Prevent parallel index build in a standalone backend.

tglsfdc · tglsfdc · commit 942e441ee8f4 · 2020-11-30T14:38:00.000-05:00
This can't work if there's no postmaster, and indeed the code got an assertion failure trying. There should be a check on IsUnderPostmaster gating the use of parallelism, as the planner has for ordinary parallel queries. Commit 40d964e got this right, so follow its model of checking IsUnderPostmaster at the same place where we check for max_parallel_maintenance_workers == 0. In general, new code implementing parallel utility operations should do the same. Report and patch by Yulin Pei, cosmetically adjusted by me. Back-patch to v11 where this code came in. Discussion: https://postgr.es/m/HK0PR01MB22747D839F77142D7E76A45DF4F50@HK0PR01MB2274.apcprd01.prod.exchangelabs.com
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
@@ -6090,8 +6090,12 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 	double		reltuples;
 	double		allvisfrac;
 
-	/* Return immediately when parallelism disabled */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE ||
+	/*
+	 * We don't allow performing parallel operation in standalone backend or
+	 * when parallelism is disabled.
+	 */
+	if (!IsUnderPostmaster ||
+		dynamic_shared_memory_type == DSM_IMPL_NONE ||
 		max_parallel_maintenance_workers == 0)
 		return 0;
 
