Add tests for intermediate results

src/test/regress/expected/shared_connection_stats.out

@@ -300,6 +300,34 @@ BEGIN;
                        16
 (2 rows)
 
+COMMIT;
+BEGIN;
+	-- now allow at most 1 connection, and ensure that intermediate
+	-- results don't require any extra connections
+	SET LOCAL citus.max_adaptive_executor_pool_size TO 1;
+	SET LOCAL citus.task_assignment_policy TO "round-robin";
+	SELECT cnt FROM (SELECT count(*) as cnt, random() FROM test LIMIT 1) as foo;
+ cnt
+---------------------------------------------------------------------
+ 101
+(1 row)
+
+	-- queries with intermediate results don't use any extra connections
+	SELECT
+		connection_count_to_node
+	FROM
+		citus_remote_connection_stats()
+	WHERE
+		port IN (SELECT node_port FROM master_get_active_worker_nodes()) AND
+		database_name = 'regression'
+	ORDER BY
+		hostname, port;
+ connection_count_to_node
+---------------------------------------------------------------------
+                        1
+                        1
+(2 rows)
+
 COMMIT;
 -- now show that when max_cached_conns_per_worker > 1
 -- Citus forces the first execution to open at least 2

src/test/regress/sql/shared_connection_stats.sql

@@ -172,6 +172,26 @@ BEGIN;
 		hostname, port;
 COMMIT;
 
+BEGIN;
+	-- now allow at most 1 connection, and ensure that intermediate
+	-- results don't require any extra connections
+	SET LOCAL citus.max_adaptive_executor_pool_size TO 1;
+	SET LOCAL citus.task_assignment_policy TO "round-robin";
+	SELECT cnt FROM (SELECT count(*) as cnt, random() FROM test LIMIT 1) as foo;
+
+	-- queries with intermediate results don't use any extra connections
+	SELECT
+		connection_count_to_node
+	FROM
+		citus_remote_connection_stats()
+	WHERE
+		port IN (SELECT node_port FROM master_get_active_worker_nodes()) AND
+		database_name = 'regression'
+	ORDER BY
+		hostname, port;
+COMMIT;
+
+
 -- now show that when max_cached_conns_per_worker > 1
 -- Citus forces the first execution to open at least 2
 -- connections that are cached. Later, that 2 cached
@@ -200,6 +220,9 @@ BEGIN;
 		hostname, port;
 COMMIT;
 
+
+
+
 -- connection_retry_timeout cannot be smaller than node_connection_timeout
 SET citus.connection_retry_timeout TO 1000;