mirror of https://github.com/citusdata/citus.git
293 lines
14 KiB
Plaintext
293 lines
14 KiB
Plaintext
--
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-- PG17
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--
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SHOW server_version \gset
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SELECT substring(:'server_version', '\d+')::int >= 17 AS server_version_ge_17
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\gset
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-- PG17 has the capabilty to pull up a correlated ANY subquery to a join if
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-- the subquery only refers to its immediate parent query. Previously, the
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-- subquery needed to be implemented as a SubPlan node, typically as a
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-- filter on a scan or join node. This PG17 capability enables Citus to
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-- run queries with correlated subqueries in certain cases, as shown here.
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-- Relevant PG commit:
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-- https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=9f1337639
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-- This feature is tested for all PG versions, not just PG17; each test query with
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-- a correlated subquery should fail with PG version < 17.0, but the test query
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-- rewritten to reflect how PG17 optimizes it should succeed with PG < 17.0
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CREATE SCHEMA pg17_corr_subq_folding;
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SET search_path TO pg17_corr_subq_folding;
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SET citus.next_shard_id TO 20240017;
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SET citus.shard_count TO 2;
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SET citus.shard_replication_factor TO 1;
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CREATE TABLE test (x int, y int);
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SELECT create_distributed_table('test', 'x');
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create_distributed_table
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---------------------------------------------------------------------
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(1 row)
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INSERT INTO test VALUES (1,1), (2,2);
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-- Query 1: WHERE clause has a correlated subquery with a UNION. PG17 can plan
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-- this as a nested loop join with the subquery as the inner. The correlation
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-- is on the distribution column so the join can be pushed down by Citus.
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explain (costs off)
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SELECT *
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FROM test a
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WHERE x IN (SELECT x FROM test b UNION SELECT y FROM test c WHERE a.x = c.x)
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ORDER BY 1,2;
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ERROR: cannot push down this subquery
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DETAIL: Complex subqueries and CTEs are not supported within a UNION
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SET client_min_messages TO DEBUG2;
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SELECT *
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FROM test a
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WHERE x IN (SELECT x FROM test b UNION SELECT y FROM test c WHERE a.x = c.x)
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ORDER BY 1,2;
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: generating subplan XXX_1 for subquery SELECT x FROM pg17_corr_subq_folding.test b
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: Plan XXX query after replacing subqueries and CTEs: SELECT x, y FROM pg17_corr_subq_folding.test a WHERE (x OPERATOR(pg_catalog.=) ANY (SELECT intermediate_result.x FROM read_intermediate_result('XXX_1'::text, 'binary'::citus_copy_format) intermediate_result(x integer) UNION SELECT c.y FROM pg17_corr_subq_folding.test c WHERE (a.x OPERATOR(pg_catalog.=) c.x))) ORDER BY x, y
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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ERROR: cannot push down this subquery
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DETAIL: Complex subqueries and CTEs are not supported within a UNION
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RESET client_min_messages;
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-- Query 1 rewritten with subquery pulled up to a join, as done by PG17 planner;
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-- this query can be run without issues by Citus with older (pre PG17) PGs.
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explain (costs off)
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SELECT a.*
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FROM test a JOIN LATERAL (SELECT x FROM test b UNION SELECT y FROM test c WHERE a.x = c.x) dt1 ON a.x = dt1.x
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ORDER BY 1,2;
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QUERY PLAN
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---------------------------------------------------------------------
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Sort
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Sort Key: remote_scan.x, remote_scan.y
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-> Custom Scan (Citus Adaptive)
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Task Count: 2
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Tasks Shown: One of 2
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-> Task
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Node: host=localhost port=xxxxx dbname=regression
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-> Nested Loop
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-> Seq Scan on test_20240017 a
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-> Subquery Scan on dt1
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Filter: (a.x = dt1.x)
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-> HashAggregate
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Group Key: b.x
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-> Append
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-> Seq Scan on test_20240017 b
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-> Seq Scan on test_20240017 c
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Filter: (a.x = x)
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(17 rows)
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SET client_min_messages TO DEBUG2;
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SELECT a.*
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FROM test a JOIN LATERAL (SELECT x FROM test b UNION SELECT y FROM test c WHERE a.x = c.x) dt1 ON a.x = dt1.x
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ORDER BY 1,2;
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DEBUG: Router planner cannot handle multi-shard select queries
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x | y
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---------------------------------------------------------------------
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1 | 1
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2 | 2
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(2 rows)
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RESET client_min_messages;
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CREATE TABLE users (user_id int, time int, dept int, info bigint);
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CREATE TABLE events (user_id int, time int, event_type int, payload text);
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select create_distributed_table('users', 'user_id');
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create_distributed_table
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---------------------------------------------------------------------
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(1 row)
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select create_distributed_table('events', 'user_id');
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create_distributed_table
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---------------------------------------------------------------------
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(1 row)
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insert into users
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select i, 2021 + (i % 3), i % 5, 99999 * i from generate_series(1, 10) i;
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insert into events
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select i % 10 + 1, 2021 + (i % 3), i %11, md5((i*i)::text) from generate_series(1, 100) i;
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-- Query 2. In Citus correlated subqueries can not be used in the WHERE
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-- clause but if the subquery can be pulled up to a join it becomes possible
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-- for Citus to run the query, per this example. Pre PG17 the suqbuery
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-- was implemented as a SubPlan filter on the events table scan.
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EXPLAIN (costs off)
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WITH event_id
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AS(SELECT user_id AS events_user_id,
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time AS events_time,
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event_type
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FROM events)
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SELECT Count(*)
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FROM event_id
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WHERE (events_user_id) IN (SELECT user_id
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FROM users
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WHERE users.time = events_time);
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ERROR: correlated subqueries are not supported when the FROM clause contains a CTE or subquery
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SET client_min_messages TO DEBUG2;
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WITH event_id
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AS(SELECT user_id AS events_user_id,
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time AS events_time,
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event_type
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FROM events)
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SELECT Count(*)
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FROM event_id
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WHERE (events_user_id) IN (SELECT user_id
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FROM users
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WHERE users.time = events_time);
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DEBUG: CTE event_id is going to be inlined via distributed planning
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: generating subplan XXX_1 for CTE event_id: SELECT user_id AS events_user_id, "time" AS events_time, event_type FROM pg17_corr_subq_folding.events
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: Plan XXX query after replacing subqueries and CTEs: SELECT count(*) AS count FROM (SELECT intermediate_result.events_user_id, intermediate_result.events_time, intermediate_result.event_type FROM read_intermediate_result('XXX_1'::text, 'binary'::citus_copy_format) intermediate_result(events_user_id integer, events_time integer, event_type integer)) event_id WHERE (events_user_id OPERATOR(pg_catalog.=) ANY (SELECT users.user_id FROM pg17_corr_subq_folding.users WHERE (users."time" OPERATOR(pg_catalog.=) event_id.events_time)))
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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ERROR: correlated subqueries are not supported when the FROM clause contains a CTE or subquery
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RESET client_min_messages;
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-- Query 2 rewritten with subquery pulled up to a join, as done by pg17 planner. Citus
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-- Citus is able to run this query with previous pg versions. Note that the CTE can be
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-- disregarded because it is inlined, being only referenced once.
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EXPLAIN (COSTS OFF)
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SELECT Count(*)
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FROM (SELECT user_id AS events_user_id,
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time AS events_time,
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event_type FROM events) dt1
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INNER JOIN (SELECT distinct user_id, time FROM users) dt
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ON events_user_id = dt.user_id and events_time = dt.time;
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QUERY PLAN
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---------------------------------------------------------------------
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Aggregate
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-> Custom Scan (Citus Adaptive)
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Task Count: 2
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Tasks Shown: One of 2
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-> Task
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Node: host=localhost port=xxxxx dbname=regression
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-> Aggregate
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-> Hash Join
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Hash Cond: ((events.user_id = users.user_id) AND (events."time" = users."time"))
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-> Seq Scan on events_20240021 events
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-> Hash
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-> HashAggregate
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Group Key: users.user_id, users."time"
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-> Seq Scan on users_20240019 users
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(14 rows)
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SET client_min_messages TO DEBUG2;
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SELECT Count(*)
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FROM (SELECT user_id AS events_user_id,
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time AS events_time,
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event_type FROM events) dt1
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INNER JOIN (SELECT distinct user_id, time FROM users) dt
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ON events_user_id = dt.user_id and events_time = dt.time;
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DEBUG: Router planner cannot handle multi-shard select queries
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count
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---------------------------------------------------------------------
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31
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(1 row)
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RESET client_min_messages;
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-- Query 3: another example where recursive planning was prevented due to
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-- correlated subqueries, but with PG17 folding the subquery to a join it is
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-- possible for Citus to plan and run the query.
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EXPLAIN (costs off)
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SELECT dept, sum(user_id) FROM
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(SELECT users.dept, users.user_id
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FROM users, events as d1
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WHERE d1.user_id = users.user_id
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AND users.dept IN (3,4)
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AND users.user_id IN
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(SELECT s2.user_id FROM users as s2
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GROUP BY d1.user_id, s2.user_id)) dt
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GROUP BY dept;
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ERROR: complex joins are only supported when all distributed tables are co-located and joined on their distribution columns
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SET client_min_messages TO DEBUG2;
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SELECT dept, sum(user_id) FROM
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(SELECT users.dept, users.user_id
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FROM users, events as d1
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WHERE d1.user_id = users.user_id
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AND users.dept IN (3,4)
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AND users.user_id IN
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(SELECT s2.user_id FROM users as s2
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GROUP BY d1.user_id, s2.user_id)) dt
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GROUP BY dept;
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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DEBUG: Router planner cannot handle multi-shard select queries
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DEBUG: skipping recursive planning for the subquery since it contains references to outer queries
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ERROR: complex joins are only supported when all distributed tables are co-located and joined on their distribution columns
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RESET client_min_messages;
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-- Query 3 rewritten in a similar way to how the PG17 pulls up the subquery;
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-- the join is on the distribution key so Citus can push down.
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EXPLAIN (costs off)
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SELECT dept, sum(user_id) FROM
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(SELECT users.dept, users.user_id
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FROM users, events as d1
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JOIN LATERAL (SELECT s2.user_id FROM users as s2
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GROUP BY s2.user_id HAVING d1.user_id IS NOT NULL) as d2 ON 1=1
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WHERE d1.user_id = users.user_id
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AND users.dept IN (3,4)
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AND users.user_id = d2.user_id) dt
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GROUP BY dept;
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QUERY PLAN
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---------------------------------------------------------------------
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HashAggregate
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Group Key: remote_scan.dept
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-> Custom Scan (Citus Adaptive)
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Task Count: 2
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Tasks Shown: One of 2
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-> Task
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Node: host=localhost port=xxxxx dbname=regression
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-> GroupAggregate
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Group Key: users.dept
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-> Sort
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Sort Key: users.dept
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-> Nested Loop
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-> Hash Join
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Hash Cond: (d1.user_id = users.user_id)
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-> Seq Scan on events_20240021 d1
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-> Hash
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-> Seq Scan on users_20240019 users
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Filter: (dept = ANY ('{3,4}'::integer[]))
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-> Subquery Scan on d2
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Filter: (d1.user_id = d2.user_id)
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-> HashAggregate
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Group Key: s2.user_id
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-> Result
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One-Time Filter: (d1.user_id IS NOT NULL)
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-> Seq Scan on users_20240019 s2
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(25 rows)
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SET client_min_messages TO DEBUG2;
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SELECT dept, sum(user_id) FROM
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(SELECT users.dept, users.user_id
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FROM users, events as d1
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JOIN LATERAL (SELECT s2.user_id FROM users as s2
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GROUP BY s2.user_id HAVING d1.user_id IS NOT NULL) as d2 ON 1=1
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WHERE d1.user_id = users.user_id
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AND users.dept IN (3,4)
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AND users.user_id = d2.user_id) dt
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GROUP BY dept;
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DEBUG: Router planner cannot handle multi-shard select queries
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dept | sum
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---------------------------------------------------------------------
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3 | 110
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4 | 130
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(2 rows)
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RESET client_min_messages;
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RESET search_path;
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DROP SCHEMA pg17_corr_subq_folding CASCADE;
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NOTICE: drop cascades to 3 other objects
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DETAIL: drop cascades to table pg17_corr_subq_folding.test
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drop cascades to table pg17_corr_subq_folding.users
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drop cascades to table pg17_corr_subq_folding.events
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\if :server_version_ge_17
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\else
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\q
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