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Merge pull request #4331 from citusdata/pre_executor_run 

Do not execute subplans multiple times with cursors
pull/4334/head
Önder Kalacı 2020-11-20 13:36:07 +01:00 committed by GitHub
parent b0ddbbd33a c433c66f2b
commit 856e5c85cf
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 350 additions and 1 deletions
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12
src/backend/distributed/executor/adaptive_executor.c
View File

@ -660,6 +660,16 @@ static void SetAttributeInputMetadata(DistributedExecution *execution,
void
AdaptiveExecutorPreExecutorRun(CitusScanState *scanState)
{
if (scanState->finishedPreScan)
{
/*
* Cursors (and hence RETURN QUERY syntax in pl/pgsql functions)
* may trigger AdaptiveExecutorPreExecutorRun() on every fetch
* operation. Though, we should only execute PreScan once.
*/
return;
}
DistributedPlan *distributedPlan = scanState->distributedPlan;
/*
@ -670,6 +680,8 @@ AdaptiveExecutorPreExecutorRun(CitusScanState *scanState)
LockPartitionsForDistributedPlan(distributedPlan);
ExecuteSubPlans(distributedPlan);
scanState->finishedPreScan = true;
}

6
src/backend/distributed/executor/citus_custom_scan.c
View File

@ -558,6 +558,9 @@ AdaptiveExecutorCreateScan(CustomScan *scan)
scanState->customScanState.methods = &AdaptiveExecutorCustomExecMethods;
scanState->PreExecScan = &CitusPreExecScan;
scanState->finishedPreScan = false;
scanState->finishedRemoteScan = false;
return (Node *) scanState;
}
@ -578,6 +581,9 @@ NonPushableInsertSelectCreateScan(CustomScan *scan)
scanState->customScanState.methods =
&NonPushableInsertSelectCustomExecMethods;
scanState->finishedPreScan = false;
scanState->finishedRemoteScan = false;
return (Node *) scanState;
}

1
src/include/distributed/citus_custom_scan.h
View File

@ -20,6 +20,7 @@ typedef struct CitusScanState
CustomScanState customScanState; /* underlying custom scan node */
/* function that gets called before postgres starts its execution */
bool finishedPreScan; /* flag to check if the pre scan is finished */
void (*PreExecScan)(struct CitusScanState *scanState);
DistributedPlan *distributedPlan; /* distributed execution plan */

218
src/test/regress/expected/cursors.out Normal file
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@ -0,0 +1,218 @@
CREATE SCHEMA cursors;
SET search_path TO cursors;
CREATE TABLE distributed_table (key int, value text);
SELECT create_distributed_table('distributed_table', 'key');
create_distributed_table
---------------------------------------------------------------------
(1 row)
-- load some data, but not very small amounts because RETURN QUERY in plpgsql
-- hard codes the cursor fetch to 50 rows on PG 12, though they might increase
-- it sometime in the future, so be mindful
INSERT INTO distributed_table SELECT i % 10, i::text FROM generate_series(0, 1000) i;
CREATE OR REPLACE FUNCTION simple_cursor_on_dist_table(cursor_name refcursor) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR SELECT DISTINCT key FROM distributed_table ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION cursor_with_intermediate_result_on_dist_table(cursor_name refcursor) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR
WITH cte_1 AS (SELECT * FROM distributed_table OFFSET 0)
SELECT DISTINCT key FROM distributed_table WHERE value in (SELECT value FROM cte_1) ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION cursor_with_intermediate_result_on_dist_table_with_param(cursor_name refcursor, filter text) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR
WITH cte_1 AS (SELECT * FROM distributed_table WHERE value < $2 OFFSET 0)
SELECT DISTINCT key FROM distributed_table WHERE value in (SELECT value FROM cte_1) ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
-- pretty basic query with cursors
-- Citus should plan/execute once and pull
-- the results to coordinator, then serve it
-- from the coordinator
BEGIN;
SELECT simple_cursor_on_dist_table('cursor_1');
simple_cursor_on_dist_table
---------------------------------------------------------------------
cursor_1
(1 row)
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 5 IN cursor_1;
key
---------------------------------------------------------------------
0
1
2
3
4
(5 rows)
FETCH 50 IN cursor_1;
key
---------------------------------------------------------------------
5
6
7
8
9
(5 rows)
FETCH ALL IN cursor_1;
key
---------------------------------------------------------------------
(0 rows)
COMMIT;
BEGIN;
SELECT cursor_with_intermediate_result_on_dist_table('cursor_1');
cursor_with_intermediate_result_on_dist_table
---------------------------------------------------------------------
cursor_1
(1 row)
-- multiple FETCH commands should not trigger re-running the subplans
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 5 IN cursor_1;
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
key
---------------------------------------------------------------------
0
1
2
3
4
(5 rows)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
5
(1 row)
FETCH ALL IN cursor_1;
key
---------------------------------------------------------------------
6
7
8
9
(4 rows)
FETCH 5 IN cursor_1;
key
---------------------------------------------------------------------
(0 rows)
COMMIT;
BEGIN;
SELECT cursor_with_intermediate_result_on_dist_table_with_param('cursor_1', '600');
cursor_with_intermediate_result_on_dist_table_with_param
---------------------------------------------------------------------
cursor_1
(1 row)
-- multiple FETCH commands should not trigger re-running the subplans
-- also test with parameters
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 1 IN cursor_1;
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
key
---------------------------------------------------------------------
0
(1 row)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
1
(1 row)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
2
(1 row)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
3
(1 row)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
4
(1 row)
FETCH 1 IN cursor_1;
key
---------------------------------------------------------------------
5
(1 row)
FETCH ALL IN cursor_1;
key
---------------------------------------------------------------------
6
7
8
9
(4 rows)
COMMIT;
CREATE OR REPLACE FUNCTION value_counter() RETURNS TABLE(counter text) LANGUAGE PLPGSQL AS $function$
BEGIN
return query
WITH cte AS
(SELECT dt.value
FROM distributed_table dt
WHERE dt.value in
(SELECT value
FROM distributed_table p
GROUP BY p.value
HAVING count(*) > 0))
SELECT * FROM cte;
END;
$function$ ;
SET citus.log_intermediate_results TO ON;
SET client_min_messages TO DEBUG1;
\set VERBOSITY terse
SELECT count(*) from (SELECT value_counter()) as foo;
DEBUG: CTE cte is going to be inlined via distributed planning
DEBUG: generating subplan XXX_1 for subquery SELECT value FROM cursors.distributed_table p GROUP BY value HAVING (count(*) OPERATOR(pg_catalog.>) 0)
DEBUG: Plan XXX query after replacing subqueries and CTEs: SELECT value FROM (SELECT dt.value FROM cursors.distributed_table dt WHERE (dt.value OPERATOR(pg_catalog.=) ANY (SELECT intermediate_result.value FROM read_intermediate_result('XXX_1'::text, 'binary'::citus_copy_format) intermediate_result(value text)))) cte
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
count
---------------------------------------------------------------------
1001
(1 row)
BEGIN;
SELECT count(*) from (SELECT value_counter()) as foo;
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
DEBUG: Subplan XXX_1 will be sent to localhost:xxxxx
count
---------------------------------------------------------------------
1001
(1 row)
COMMIT;
-- suppress NOTICEs
SET client_min_messages TO ERROR;
DROP SCHEMA cursors CASCADE;

2
src/test/regress/multi_schedule
View File

@ -108,7 +108,7 @@ test: ch_bench_subquery_repartition
test: multi_agg_type_conversion multi_count_type_conversion
test: multi_partition_pruning single_hash_repartition_join
test: multi_join_pruning multi_hash_pruning intermediate_result_pruning
test: multi_null_minmax_value_pruning
test: multi_null_minmax_value_pruning cursors
test: multi_query_directory_cleanup
test: multi_task_assignment_policy multi_cross_shard
test: multi_utility_statements

112
src/test/regress/sql/cursors.sql Normal file
View File

@ -0,0 +1,112 @@
CREATE SCHEMA cursors;
SET search_path TO cursors;
CREATE TABLE distributed_table (key int, value text);
SELECT create_distributed_table('distributed_table', 'key');
-- load some data, but not very small amounts because RETURN QUERY in plpgsql
-- hard codes the cursor fetch to 50 rows on PG 12, though they might increase
-- it sometime in the future, so be mindful
INSERT INTO distributed_table SELECT i % 10, i::text FROM generate_series(0, 1000) i;
CREATE OR REPLACE FUNCTION simple_cursor_on_dist_table(cursor_name refcursor) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR SELECT DISTINCT key FROM distributed_table ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION cursor_with_intermediate_result_on_dist_table(cursor_name refcursor) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR
WITH cte_1 AS (SELECT * FROM distributed_table OFFSET 0)
SELECT DISTINCT key FROM distributed_table WHERE value in (SELECT value FROM cte_1) ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
CREATE OR REPLACE FUNCTION cursor_with_intermediate_result_on_dist_table_with_param(cursor_name refcursor, filter text) RETURNS refcursor AS '
BEGIN
OPEN $1 FOR
WITH cte_1 AS (SELECT * FROM distributed_table WHERE value < $2 OFFSET 0)
SELECT DISTINCT key FROM distributed_table WHERE value in (SELECT value FROM cte_1) ORDER BY 1;
RETURN $1;
END;
' LANGUAGE plpgsql;
-- pretty basic query with cursors
-- Citus should plan/execute once and pull
-- the results to coordinator, then serve it
-- from the coordinator
BEGIN;
SELECT simple_cursor_on_dist_table('cursor_1');
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 5 IN cursor_1;
FETCH 50 IN cursor_1;
FETCH ALL IN cursor_1;
COMMIT;
BEGIN;
SELECT cursor_with_intermediate_result_on_dist_table('cursor_1');
-- multiple FETCH commands should not trigger re-running the subplans
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 5 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH ALL IN cursor_1;
FETCH 5 IN cursor_1;
COMMIT;
BEGIN;
SELECT cursor_with_intermediate_result_on_dist_table_with_param('cursor_1', '600');
-- multiple FETCH commands should not trigger re-running the subplans
-- also test with parameters
SET LOCAL citus.log_intermediate_results TO ON;
SET LOCAL client_min_messages TO DEBUG1;
FETCH 1 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH 1 IN cursor_1;
FETCH ALL IN cursor_1;
COMMIT;
CREATE OR REPLACE FUNCTION value_counter() RETURNS TABLE(counter text) LANGUAGE PLPGSQL AS $function$
BEGIN
return query
WITH cte AS
(SELECT dt.value
FROM distributed_table dt
WHERE dt.value in
(SELECT value
FROM distributed_table p
GROUP BY p.value
HAVING count(*) > 0))
SELECT * FROM cte;
END;
$function$ ;
SET citus.log_intermediate_results TO ON;
SET client_min_messages TO DEBUG1;
\set VERBOSITY terse
SELECT count(*) from (SELECT value_counter()) as foo;
BEGIN;
SELECT count(*) from (SELECT value_counter()) as foo;
COMMIT;
-- suppress NOTICEs
SET client_min_messages TO ERROR;
DROP SCHEMA cursors CASCADE;