INSERT .. SELECT pushdown honors multi_shard_modification_mode

src/backend/distributed/executor/citus_custom_scan.c

@@ -213,11 +213,10 @@ RouterCreateScan(CustomScan *scan)
 		Assert(isModificationQuery);
 
 		if (IsMultiRowInsert(workerJob->jobQuery) ||
-			(IsUpdateOrDelete(distributedPlan) &&
-			 MultiShardConnectionType == SEQUENTIAL_CONNECTION))
+			MultiShardConnectionType == SEQUENTIAL_CONNECTION)
 		{
 			/*
-			 * Multi shard update deletes while multi_shard_modify_mode equals
+			 * Multi shard modifications while multi_shard_modify_mode equals
 			 * to 'sequential' or Multi-row INSERT are executed sequentially
 			 * instead of using parallel connections.
 			 */

src/test/regress/expected/multi_insert_select.out

@@ -1717,13 +1717,20 @@ ROLLBACK;
 -- Altering a reference table and then performing an INSERT ... SELECT which
 -- joins with the reference table is not allowed, since the INSERT ... SELECT
 -- would read from the reference table over others connections than the ones
--- that performed the DDL.
+-- that performed the parallel DDL.
 BEGIN;
 ALTER TABLE reference_table ADD COLUMN z int;
 INSERT INTO raw_events_first (user_id)
 SELECT user_id FROM raw_events_second JOIN reference_table USING (user_id);
 ERROR:  cannot establish a new connection for placement 13300025, since DDL has been executed on a connection that is in use
 ROLLBACK;
+-- the same test with sequential DDL should work fine
+BEGIN;
+SET LOCAL citus.multi_shard_modify_mode TO 'sequential';
+ALTER TABLE reference_table ADD COLUMN z int;
+INSERT INTO raw_events_first (user_id)
+SELECT user_id FROM raw_events_second JOIN reference_table USING (user_id);
+ROLLBACK;
 -- Insert after copy is allowed
 BEGIN;
 COPY raw_events_second (user_id, value_1) FROM STDIN DELIMITER ',';

src/test/regress/expected/sequential_modifications.out

@@ -416,6 +416,51 @@ SELECT count(*) FROM multi_shard_modify_test;
      0
 (1 row)
 
+-- test INSERT ... SELECT queries
+-- with sequential modification mode, we should see #primary worker records
+SET citus.multi_shard_modify_mode TO 'sequential';
+SELECT recover_prepared_transactions();
+ recover_prepared_transactions 
+-------------------------------
+                             0
+(1 row)
+
+INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+SELECT distributed_2PCs_are_equal_to_worker_count();
+ distributed_2pcs_are_equal_to_worker_count 
+--------------------------------------------
+ t
+(1 row)
+
+SET citus.multi_shard_modify_mode TO 'parallel';
+SELECT recover_prepared_transactions();
+ recover_prepared_transactions 
+-------------------------------
+                             0
+(1 row)
+
+INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+SELECT distributed_2PCs_are_equal_to_placement_count();
+ distributed_2pcs_are_equal_to_placement_count 
+-----------------------------------------------
+ t
+(1 row)
+
+-- one more realistic test with sequential inserts and INSERT .. SELECT in the same tx
+INSERT INTO multi_shard_modify_test SELECT i, i::text, i FROM generate_series(0,100) i;
+BEGIN;
+    INSERT INTO multi_shard_modify_test VALUES (1,'1',1), (2,'2',2), (3,'3',3), (4,'4',4);
+    -- now switch to sequential mode to enable a successful INSERT .. SELECT
+    SET LOCAL citus.multi_shard_modify_mode TO 'sequential';
+    INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+COMMIT;
+-- see that all the data successfully inserted
+SELECT count(*) FROM multi_shard_modify_test;
+ count 
+-------
+   210
+(1 row)
+
 ALTER SYSTEM SET citus.recover_2pc_interval TO DEFAULT;
 SET citus.shard_replication_factor TO DEFAULT;
 SELECT pg_reload_conf();

src/test/regress/sql/multi_insert_select.sql

@@ -1361,13 +1361,21 @@ ROLLBACK;
 -- Altering a reference table and then performing an INSERT ... SELECT which
 -- joins with the reference table is not allowed, since the INSERT ... SELECT
 -- would read from the reference table over others connections than the ones
--- that performed the DDL.
+-- that performed the parallel DDL.
 BEGIN;
 ALTER TABLE reference_table ADD COLUMN z int;
 INSERT INTO raw_events_first (user_id)
 SELECT user_id FROM raw_events_second JOIN reference_table USING (user_id);
 ROLLBACK;
 
+-- the same test with sequential DDL should work fine
+BEGIN;
+SET LOCAL citus.multi_shard_modify_mode TO 'sequential';
+ALTER TABLE reference_table ADD COLUMN z int;
+INSERT INTO raw_events_first (user_id)
+SELECT user_id FROM raw_events_second JOIN reference_table USING (user_id);
+ROLLBACK;
+
 -- Insert after copy is allowed
 BEGIN;
 COPY raw_events_second (user_id, value_1) FROM STDIN DELIMITER ',';

src/test/regress/sql/sequential_modifications.sql

@@ -219,6 +219,30 @@ COMMIT;
 -- see that all the data successfully removed
 SELECT count(*) FROM multi_shard_modify_test;
 
+-- test INSERT ... SELECT queries
+-- with sequential modification mode, we should see #primary worker records
+SET citus.multi_shard_modify_mode TO 'sequential';
+SELECT recover_prepared_transactions();
+INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+SELECT distributed_2PCs_are_equal_to_worker_count();
+
+SET citus.multi_shard_modify_mode TO 'parallel';
+SELECT recover_prepared_transactions();
+INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+SELECT distributed_2PCs_are_equal_to_placement_count();
+
+-- one more realistic test with sequential inserts and INSERT .. SELECT in the same tx
+INSERT INTO multi_shard_modify_test SELECT i, i::text, i FROM generate_series(0,100) i;
+BEGIN;
+    INSERT INTO multi_shard_modify_test VALUES (1,'1',1), (2,'2',2), (3,'3',3), (4,'4',4);
+
+    -- now switch to sequential mode to enable a successful INSERT .. SELECT
+    SET LOCAL citus.multi_shard_modify_mode TO 'sequential';
+    INSERT INTO multi_shard_modify_test SELECT * FROM multi_shard_modify_test;
+COMMIT;
+
+-- see that all the data successfully inserted
+SELECT count(*) FROM multi_shard_modify_test;
 
 ALTER SYSTEM SET citus.recover_2pc_interval TO DEFAULT;
 SET citus.shard_replication_factor TO DEFAULT;