Rework some error strings for REINDEX CONCURRENTLY with system catalogs

This makes the whole user experience more consistent when bumping into
failures, and more in line with the rewording done via 508300e.

Author: Michael Paquier
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/20190514153252.GA22168@alvherre.pgsql

src/backend/commands/indexcmds.c

@@ -2499,7 +2499,7 @@ ReindexMultipleTables(const char *objectName, ReindexObjectType objectKind,
 	if (objectKind == REINDEX_OBJECT_SYSTEM && concurrent)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("concurrent reindex of system catalogs is not supported")));
+				 errmsg("cannot reindex system catalogs concurrently")));
 
 	/*
 	 * Get OID of object to reindex, being the database currently being used
@@ -2613,7 +2613,7 @@ ReindexMultipleTables(const char *objectName, ReindexObjectType objectKind,
 			if (!concurrent_warning)
 				ereport(WARNING,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						 errmsg("concurrent reindex is not supported for catalog relations, skipping all")));
+						 errmsg("cannot reindex system catalogs concurrently, skipping all")));
 			concurrent_warning = true;
 			continue;
 		}
@@ -2764,11 +2764,10 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 
 				MemoryContextSwitchTo(oldcontext);
 
-				/* A system catalog cannot be reindexed concurrently */
 				if (IsCatalogRelationOid(relationOid))
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("cannot reindex a system catalog concurrently")));
+							 errmsg("cannot reindex system catalogs concurrently")));
 
 				/* Open relation to get its indexes */
 				heapRelation = table_open(relationOid, ShareUpdateExclusiveLock);
@@ -2858,11 +2857,10 @@ ReindexRelationConcurrently(Oid relationOid, int options)
 			{
 				Oid			heapId = IndexGetRelation(relationOid, false);
 
-				/* A system catalog cannot be reindexed concurrently */
 				if (IsCatalogRelationOid(heapId))
 					ereport(ERROR,
 							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("cannot reindex a system catalog concurrently")));
+							 errmsg("cannot reindex system catalogs concurrently")));
 
 				/* Save the list of relation OIDs in private context */
 				oldcontext = MemoryContextSwitchTo(private_context);

src/test/regress/expected/create_index.out

@@ -2093,19 +2093,19 @@ REINDEX TABLE CONCURRENTLY concur_reindex_tab;
 ERROR:  REINDEX CONCURRENTLY cannot run inside a transaction block
 COMMIT;
 REINDEX TABLE CONCURRENTLY pg_class; -- no catalog relation
-ERROR:  cannot reindex a system catalog concurrently
+ERROR:  cannot reindex system catalogs concurrently
 REINDEX INDEX CONCURRENTLY pg_class_oid_index; -- no catalog index
-ERROR:  cannot reindex a system catalog concurrently
+ERROR:  cannot reindex system catalogs concurrently
 -- These are the toast table and index of pg_authid.
 REINDEX TABLE CONCURRENTLY pg_toast.pg_toast_1260; -- no catalog toast table
-ERROR:  cannot reindex a system catalog concurrently
+ERROR:  cannot reindex system catalogs concurrently
 REINDEX INDEX CONCURRENTLY pg_toast.pg_toast_1260_index; -- no catalog toast index
-ERROR:  cannot reindex a system catalog concurrently
+ERROR:  cannot reindex system catalogs concurrently
 REINDEX SYSTEM CONCURRENTLY postgres; -- not allowed for SYSTEM
-ERROR:  concurrent reindex of system catalogs is not supported
+ERROR:  cannot reindex system catalogs concurrently
 -- Warns about catalog relations
 REINDEX SCHEMA CONCURRENTLY pg_catalog;
-WARNING:  concurrent reindex is not supported for catalog relations, skipping all
+WARNING:  cannot reindex system catalogs concurrently, skipping all
 -- Check the relation status, there should not be invalid indexes
 \d concur_reindex_tab
          Table "public.concur_reindex_tab"