Not invalidate fkey cache if citus not installed (#4521)

src/backend/distributed/metadata/metadata_cache.c

@@ -3596,6 +3596,15 @@ InvalidateForeignRelationGraphCacheCallback(Datum argument, Oid relationId)
 void
 InvalidateForeignKeyGraph(void)
 {
+	if (!CitusHasBeenLoaded())
+	{
+		/*
+		 * We should not try to invalidate foreign key graph
+		 * if citus is not loaded.
+		 */
+		return;
+	}
+
 	CitusInvalidateRelcacheByRelid(DistColocationRelationId());
 
 	/* bump command counter to force invalidation to take effect */

src/test/regress/expected/multi_drop_extension.out

@@ -18,6 +18,36 @@ SET client_min_messages TO 'WARNING';
 DROP FUNCTION pg_catalog.master_create_worker_shards;
 DROP EXTENSION citus CASCADE;
 RESET client_min_messages;
+BEGIN;
+  SET client_min_messages TO ERROR;
+  SET search_path TO public;
+  CREATE EXTENSION citus;
+  SET citus.replicate_reference_tables_on_activate TO OFF;
+  SELECT 1 FROM master_add_node('localhost', :master_port, groupId => 0);
+ ?column?
+---------------------------------------------------------------------
+        1
+(1 row)
+
+  create table l1 (a int unique);
+  SELECT create_reference_table('l1');
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+  create schema other_schema;
+  create table other_schema.l3 (a int);
+  select create_reference_table ('other_schema.l3');
+ create_reference_table
+---------------------------------------------------------------------
+
+(1 row)
+
+  alter table other_schema.l3 add constraint fkey foreign key (a) references l1(a);
+  -- show that works fine
+  drop schema public cascade;
+ROLLBACK;
 CREATE EXTENSION citus;
 -- this function is dropped in Citus10, added here for tests
 CREATE OR REPLACE FUNCTION pg_catalog.master_create_worker_shards(table_name text, shard_count integer,

src/test/regress/sql/multi_drop_extension.sql

@@ -19,6 +19,28 @@ DROP FUNCTION pg_catalog.master_create_worker_shards;
 DROP EXTENSION citus CASCADE;
 RESET client_min_messages;
 
+BEGIN;
+  SET client_min_messages TO ERROR;
+  SET search_path TO public;
+  CREATE EXTENSION citus;
+
+  -- not wait for replicating reference tables from other test files
+  SET citus.replicate_reference_tables_on_activate TO OFF;
+  SELECT 1 FROM master_add_node('localhost', :master_port, groupId => 0);
+
+  create table l1 (a int unique);
+  SELECT create_reference_table('l1');
+
+  create schema other_schema;
+  create table other_schema.l3 (a int);
+  select create_reference_table ('other_schema.l3');
+
+  alter table other_schema.l3 add constraint fkey foreign key (a) references l1(a);
+
+  -- show that works fine
+  drop schema public cascade;
+ROLLBACK;
+
 CREATE EXTENSION citus;
 -- this function is dropped in Citus10, added here for tests
 CREATE OR REPLACE FUNCTION pg_catalog.master_create_worker_shards(table_name text, shard_count integer,