Filter: (y = t1.y)

(9 rows)

-- Employ parallel join using CustomScan as an inner

EXPLAIN (COSTS OFF)

SELECT count(*) FROM parallel_test t1 NATURAL JOIN parallel_test_tmp_2 t2

WHERE t1.x < 10;

QUERY PLAN

----------------------------------------------------------------------------------------------

Aggregate

-> Gather

Workers Planned: 3

-> Nested Loop

-> Parallel Seq Scan on parallel_test t1

Filter: (x < 10)

-> Custom Scan (nodeCustomTempScan)

-> Index Scan using parallel_test_tmp_2_x_idx on parallel_test_tmp_2 t2

Index Cond: (x = t1.x)

Filter: (t1.y = y)

(10 rows)

-- Check real execution

EXPLAIN (VERBOSE, COSTS OFF)

SELECT count(*) FROM parallel_test t1 NATURAL JOIN parallel_test_tmp_2 t2;

QUERY PLAN

--------------------------------------------------------------------------

Aggregate

Output: count(*)

-> Gather

Workers Planned: 3

-> Hash Join

Hash Cond: ((t1.x = t2.x) AND (t1.y = t2.y))

-> Parallel Seq Scan on public.parallel_test t1

Output: t1.x, t1.y

-> Hash

Output: t2.x, t2.y

-> Custom Scan (nodeCustomTempScan)

Output: t2.x, t2.y

-> Seq Scan on pg_temp.parallel_test_tmp_2 t2

Output: t2.x, t2.y

(14 rows)

SET max_parallel_workers_per_gather = 0;

SELECT count(*) FROM parallel_test t1 NATURAL JOIN parallel_test_tmp_2 t2;

count

-------

10100

(1 row)

SET max_parallel_workers_per_gather = 3;

EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF, SUMMARY OFF)

SELECT count(*) FROM parallel_test t1 NATURAL JOIN parallel_test_tmp_2 t2;

QUERY PLAN

----------------------------------------------------------------------------------------------

Aggregate (actual rows=1 loops=1)

-> Gather (actual rows=10100 loops=1)

Workers Planned: 3

Workers Launched: 3

-> Hash Join (actual rows=2525 loops=4)

Hash Cond: ((t1.x = t2.x) AND (t1.y = t2.y))

-> Parallel Seq Scan on parallel_test t1 (actual rows=2525 loops=4)

-> Hash (actual rows=10100 loops=4)

Buckets: 16384 Batches: 1 Memory Usage: 571kB

-> Custom Scan (nodeCustomTempScan) (actual rows=10100 loops=4)

-> Seq Scan on parallel_test_tmp_2 t2 (actual rows=10100 loops=1)

(11 rows)

SELECT count(*) FROM parallel_test t1 NATURAL JOIN parallel_test_tmp_2 t2;

count

-------

10100

(1 row)

RESET tempscan.enable;

DROP TABLE parallel_test, parallel_test_tmp;