Fix task copy and appending empty task in ExtractLocalAndRemoteTasks (#3802)

* Not append empty task in ExtractLocalAndRemoteTasks

ExtractLocalAndRemoteTasks extracts the local and remote tasks. If we do
not have a local task the localTaskPlacementList will be NIL, in this
case we should not append anything to local tasks. Previously we would
first check if a task contains a single placement or not, now we first
check if there is any local task before doing anything.

* fix copy of node task

Task node has task query, which might contain a list of strings in its
fields. We were using postgres copyObject for these lists. Postgres
assumes that each element of list will be a node type. If it is not a
node type it will error.

As a solution to that, a new macro is introduced to copy a list of
strings.

src/backend/distributed/executor/local_executor.c

@@ -468,29 +468,19 @@ ExtractLocalAndRemoteTasks(bool readOnly, List *taskList, List **localTaskList,
 		/* either the local or the remote should be non-nil */
 		Assert(!(localTaskPlacementList == NIL && remoteTaskPlacementList == NIL));
 
-		if (list_length(task->taskPlacementList) == 1)
-		{
-			/*
-			 * At this point, the task has a single placement (e.g,. anchor shard
-			 * is distributed table's shard). So, it is either added to local or
-			 * remote taskList.
-			 */
 		if (localTaskPlacementList == NIL)
 		{
 			*remoteTaskList = lappend(*remoteTaskList, task);
 		}
-			else
+		else if (remoteTaskPlacementList == NIL)
 		{
 			*localTaskList = lappend(*localTaskList, task);
 		}
-		}
 		else
 		{
 			/*
-			 * At this point, we're dealing with reference tables or intermediate
+			 * At this point, we're dealing with a task that has placements on both
-			 * results where the task has placements on both local and remote
+			 * local and remote nodes.
-			 * nodes. We always prefer to use local placement, and require remote
-			 * placements only for modifications.
 			 */
 			task->partiallyLocalOrRemote = true;
 
@@ -505,6 +495,8 @@ ExtractLocalAndRemoteTasks(bool readOnly, List *taskList, List **localTaskList,
 			}
 			else
 			{
+				/* since shard replication factor > 1, we should have at least 1 remote task */
+				Assert(remoteTaskPlacementList != NIL);
 				Task *remoteTask = copyObject(task);
 				remoteTask->taskPlacementList = remoteTaskPlacementList;
 

src/backend/distributed/utils/citus_copyfuncs.c

@@ -14,6 +14,7 @@
 
 #include "distributed/citus_nodefuncs.h"
 #include "distributed/multi_server_executor.h"
+#include "distributed/listutils.h"
 #include "utils/datum.h"
 
 
@@ -73,6 +74,18 @@ CitusSetTag(Node *node, int tag)
 	} \
 	while (0)
 
+#define COPY_STRING_LIST(fldname) \
+	do { \
+		char *curString = NULL; \
+		List *newList = NIL; \
+		foreach_ptr(curString, from->fldname) { \
+			char *newString = curString ? pstrdup(curString) : (char *) NULL; \
+			newList = lappend(newList, newString); \
+		} \
+		newnode->fldname = newList; \
+	} \
+	while (0)
+
 static void CopyTaskQuery(Task *newnode, Task *from);
 
 static void
@@ -271,13 +284,13 @@ CopyTaskQuery(Task *newnode, Task *from)
 
 		case TASK_QUERY_TEXT_PER_PLACEMENT:
 		{
-			COPY_NODE_FIELD(taskQuery.data.perPlacementQueryStrings);
+			COPY_STRING_LIST(taskQuery.data.perPlacementQueryStrings);
 			break;
 		}
 
 		case TASK_QUERY_TEXT_LIST:
 		{
-			COPY_NODE_FIELD(taskQuery.data.queryStringList);
+			COPY_STRING_LIST(taskQuery.data.queryStringList);
 			break;
 		}
 

src/test/regress/expected/coordinator_shouldhaveshards.out

@@ -375,13 +375,48 @@ NOTICE:  executing the command locally: SELECT a.count, b.x, b.y, c.a, c.b, d.co
    100 | 3 | 2 | 3 | 2 |     1
 (1 row)
 
+-- issue #3801
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE dist_table(a int);
+ERROR:  relation "dist_table" already exists
+SELECT create_distributed_table('dist_table', 'a');
+NOTICE:  Copying data from local table...
+NOTICE:  copying the data has completed
+DETAIL:  The local data in the table is no longer visible, but is still on disk.
+HINT:  To remove the local data, run: SELECT truncate_local_data_after_distributing_table($$coordinator_shouldhaveshards.dist_table$$)
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+BEGIN;
+-- this will use perPlacementQueryStrings, make sure it works correctly with
+-- copying task
+INSERT INTO dist_table SELECT a + 1 FROM dist_table;
+ROLLBACK;
+BEGIN;
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE dist_table1(a int);
+-- this will use queryStringList, make sure it works correctly with
+-- copying task
+SELECT create_distributed_table('dist_table1', 'a');
+NOTICE:  executing the command locally: SELECT worker_apply_shard_ddl_command (1503023, 'coordinator_shouldhaveshards', 'CREATE TABLE coordinator_shouldhaveshards.dist_table1 (a integer)');SELECT worker_apply_shard_ddl_command (1503023, 'coordinator_shouldhaveshards', 'ALTER TABLE coordinator_shouldhaveshards.dist_table1 OWNER TO postgres')
+NOTICE:  executing the command locally: SELECT worker_apply_shard_ddl_command (1503025, 'coordinator_shouldhaveshards', 'CREATE TABLE coordinator_shouldhaveshards.dist_table1 (a integer)');SELECT worker_apply_shard_ddl_command (1503025, 'coordinator_shouldhaveshards', 'ALTER TABLE coordinator_shouldhaveshards.dist_table1 OWNER TO postgres')
+NOTICE:  executing the command locally: SELECT worker_apply_shard_ddl_command (1503026, 'coordinator_shouldhaveshards', 'CREATE TABLE coordinator_shouldhaveshards.dist_table1 (a integer)');SELECT worker_apply_shard_ddl_command (1503026, 'coordinator_shouldhaveshards', 'ALTER TABLE coordinator_shouldhaveshards.dist_table1 OWNER TO postgres')
+NOTICE:  executing the command locally: SELECT worker_apply_shard_ddl_command (1503028, 'coordinator_shouldhaveshards', 'CREATE TABLE coordinator_shouldhaveshards.dist_table1 (a integer)');SELECT worker_apply_shard_ddl_command (1503028, 'coordinator_shouldhaveshards', 'ALTER TABLE coordinator_shouldhaveshards.dist_table1 OWNER TO postgres')
+ create_distributed_table
+---------------------------------------------------------------------
+
+(1 row)
+
+ROLLBACK;
 RESET citus.enable_cte_inlining;
 DELETE FROM test;
 DROP TABLE test;
+DROP TABLE dist_table;
 DROP SCHEMA coordinator_shouldhaveshards CASCADE;
-NOTICE:  drop cascades to 4 other objects
+NOTICE:  drop cascades to 3 other objects
-DETAIL:  drop cascades to table dist_table
+DETAIL:  drop cascades to table ref
-drop cascades to table ref
 drop cascades to table ref_1503016
 drop cascades to table local
 SELECT 1 FROM master_set_node_property('localhost', :master_port, 'shouldhaveshards', false);

src/test/regress/expected/multi_reference_table.out

@@ -1639,6 +1639,15 @@ ORDER BY 1;
                                  ->  Seq Scan on colocated_table_test_1250005 colocated_table_test
 (25 rows)
 
+WITH a as (SELECT rt.value_2 FROM reference_table_test rt where rt.value_2 = 2)
+SELECT ct.value_1, count(*) FROM colocated_table_test ct join a on ct.value_1 = a.value_2
+WHERE exists (select * from a)
+GROUP BY 1 ORDER BY 1;
+ value_1 | count
+---------------------------------------------------------------------
+       2 |     5
+(1 row)
+
 -- clean up tables, ...
 SET client_min_messages TO ERROR;
 DROP SEQUENCE example_ref_value_seq;

src/test/regress/sql/coordinator_shouldhaveshards.sql

@@ -155,11 +155,29 @@ SELECT * FROM ref JOIN local ON (a = x);
 -- in postgres we wouldn't see this modifying cte, so it is consistent with postgres.
 WITH a AS (SELECT count(*) FROM test), b AS (INSERT INTO local VALUES (3,2) RETURNING *), c AS (INSERT INTO ref VALUES (3,2) RETURNING *), d AS (SELECT count(*) FROM ref JOIN local ON (a = x)) SELECT * FROM a, b, c, d ORDER BY x,y,a,b;
 
+-- issue #3801
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE dist_table(a int);
+SELECT create_distributed_table('dist_table', 'a');
+BEGIN;
+-- this will use perPlacementQueryStrings, make sure it works correctly with
+-- copying task
+INSERT INTO dist_table SELECT a + 1 FROM dist_table;
+ROLLBACK;
+
+BEGIN;
+SET citus.shard_replication_factor TO 2;
+CREATE TABLE dist_table1(a int);
+-- this will use queryStringList, make sure it works correctly with
+-- copying task
+SELECT create_distributed_table('dist_table1', 'a');
+ROLLBACK;
 
 RESET citus.enable_cte_inlining;
 
 DELETE FROM test;
 DROP TABLE test;
+DROP TABLE dist_table;
 
 DROP SCHEMA coordinator_shouldhaveshards CASCADE;
 

src/test/regress/sql/multi_reference_table.sql

@@ -1012,6 +1012,11 @@ EXPLAIN (COSTS OFF) SELECT value_1, count(*) FROM colocated_table_test GROUP BY
 HAVING (SELECT rt.value_2 FROM reference_table_test rt where rt.value_2 = 2) > 0
 ORDER BY 1;
 
+WITH a as (SELECT rt.value_2 FROM reference_table_test rt where rt.value_2 = 2)
+SELECT ct.value_1, count(*) FROM colocated_table_test ct join a on ct.value_1 = a.value_2
+WHERE exists (select * from a)
+GROUP BY 1 ORDER BY 1;
+
 -- clean up tables, ...
 SET client_min_messages TO ERROR;
 DROP SEQUENCE example_ref_value_seq;