1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
|
--
-- PARALLEL
--
create function sp_parallel_restricted(int) returns int as
$$begin return $1; end$$ language plpgsql parallel restricted;
-- Serializable isolation would disable parallel query, so explicitly use an
-- arbitrary other level.
begin isolation level repeatable read;
-- encourage use of parallel plans
set parallel_setup_cost=0;
set parallel_tuple_cost=0;
set min_parallel_table_scan_size=0;
set max_parallel_workers_per_gather=4;
-- Parallel Append with partial-subplans
explain (costs off)
select round(avg(aa)), sum(aa) from a_star;
QUERY PLAN
-----------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 3
-> Partial Aggregate
-> Parallel Append
-> Parallel Seq Scan on d_star
-> Parallel Seq Scan on f_star
-> Parallel Seq Scan on e_star
-> Parallel Seq Scan on b_star
-> Parallel Seq Scan on c_star
-> Parallel Seq Scan on a_star
(11 rows)
select round(avg(aa)), sum(aa) from a_star a1;
round | sum
-------+-----
14 | 355
(1 row)
-- Parallel Append with both partial and non-partial subplans
alter table c_star set (parallel_workers = 0);
alter table d_star set (parallel_workers = 0);
explain (costs off)
select round(avg(aa)), sum(aa) from a_star;
QUERY PLAN
-----------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 3
-> Partial Aggregate
-> Parallel Append
-> Seq Scan on d_star
-> Seq Scan on c_star
-> Parallel Seq Scan on f_star
-> Parallel Seq Scan on e_star
-> Parallel Seq Scan on b_star
-> Parallel Seq Scan on a_star
(11 rows)
select round(avg(aa)), sum(aa) from a_star a2;
round | sum
-------+-----
14 | 355
(1 row)
-- Parallel Append with only non-partial subplans
alter table a_star set (parallel_workers = 0);
alter table b_star set (parallel_workers = 0);
alter table e_star set (parallel_workers = 0);
alter table f_star set (parallel_workers = 0);
explain (costs off)
select round(avg(aa)), sum(aa) from a_star;
QUERY PLAN
--------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 3
-> Partial Aggregate
-> Parallel Append
-> Seq Scan on d_star
-> Seq Scan on f_star
-> Seq Scan on e_star
-> Seq Scan on b_star
-> Seq Scan on c_star
-> Seq Scan on a_star
(11 rows)
select round(avg(aa)), sum(aa) from a_star a3;
round | sum
-------+-----
14 | 355
(1 row)
-- Disable Parallel Append
alter table a_star reset (parallel_workers);
alter table b_star reset (parallel_workers);
alter table c_star reset (parallel_workers);
alter table d_star reset (parallel_workers);
alter table e_star reset (parallel_workers);
alter table f_star reset (parallel_workers);
set enable_parallel_append to off;
explain (costs off)
select round(avg(aa)), sum(aa) from a_star;
QUERY PLAN
-----------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 1
-> Partial Aggregate
-> Append
-> Parallel Seq Scan on a_star
-> Parallel Seq Scan on b_star
-> Parallel Seq Scan on c_star
-> Parallel Seq Scan on d_star
-> Parallel Seq Scan on e_star
-> Parallel Seq Scan on f_star
(11 rows)
select round(avg(aa)), sum(aa) from a_star a4;
round | sum
-------+-----
14 | 355
(1 row)
reset enable_parallel_append;
-- Parallel Append that runs serially
create function sp_test_func() returns setof text as
$$ select 'foo'::varchar union all select 'bar'::varchar $$
language sql stable;
select sp_test_func() order by 1;
sp_test_func
--------------
bar
foo
(2 rows)
-- test with leader participation disabled
set parallel_leader_participation = off;
explain (costs off)
select count(*) from tenk1 where stringu1 = 'GRAAAA';
QUERY PLAN
---------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Seq Scan on tenk1
Filter: (stringu1 = 'GRAAAA'::name)
(6 rows)
select count(*) from tenk1 where stringu1 = 'GRAAAA';
count
-------
15
(1 row)
-- test with leader participation disabled, but no workers available (so
-- the leader will have to run the plan despite the setting)
set max_parallel_workers = 0;
explain (costs off)
select count(*) from tenk1 where stringu1 = 'GRAAAA';
QUERY PLAN
---------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Seq Scan on tenk1
Filter: (stringu1 = 'GRAAAA'::name)
(6 rows)
select count(*) from tenk1 where stringu1 = 'GRAAAA';
count
-------
15
(1 row)
reset max_parallel_workers;
reset parallel_leader_participation;
-- test that parallel_restricted function doesn't run in worker
alter table tenk1 set (parallel_workers = 4);
explain (verbose, costs off)
select sp_parallel_restricted(unique1) from tenk1
where stringu1 = 'GRAAAA' order by 1;
QUERY PLAN
---------------------------------------------------------
Sort
Output: (sp_parallel_restricted(unique1))
Sort Key: (sp_parallel_restricted(tenk1.unique1))
-> Gather
Output: sp_parallel_restricted(unique1)
Workers Planned: 4
-> Parallel Seq Scan on public.tenk1
Output: unique1
Filter: (tenk1.stringu1 = 'GRAAAA'::name)
(9 rows)
-- test parallel plan when group by expression is in target list.
explain (costs off)
select length(stringu1) from tenk1 group by length(stringu1);
QUERY PLAN
---------------------------------------------------
Finalize HashAggregate
Group Key: (length((stringu1)::text))
-> Gather
Workers Planned: 4
-> Partial HashAggregate
Group Key: length((stringu1)::text)
-> Parallel Seq Scan on tenk1
(7 rows)
select length(stringu1) from tenk1 group by length(stringu1);
length
--------
6
(1 row)
explain (costs off)
select stringu1, count(*) from tenk1 group by stringu1 order by stringu1;
QUERY PLAN
----------------------------------------------------
Sort
Sort Key: stringu1
-> Finalize HashAggregate
Group Key: stringu1
-> Gather
Workers Planned: 4
-> Partial HashAggregate
Group Key: stringu1
-> Parallel Seq Scan on tenk1
(9 rows)
-- test that parallel plan for aggregates is not selected when
-- target list contains parallel restricted clause.
explain (costs off)
select sum(sp_parallel_restricted(unique1)) from tenk1
group by(sp_parallel_restricted(unique1));
QUERY PLAN
-------------------------------------------------------------------
HashAggregate
Group Key: sp_parallel_restricted(unique1)
-> Gather
Workers Planned: 4
-> Parallel Index Only Scan using tenk1_unique1 on tenk1
(5 rows)
-- test prepared statement
prepare tenk1_count(integer) As select count((unique1)) from tenk1 where hundred > $1;
explain (costs off) execute tenk1_count(1);
QUERY PLAN
----------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Seq Scan on tenk1
Filter: (hundred > 1)
(6 rows)
execute tenk1_count(1);
count
-------
9800
(1 row)
deallocate tenk1_count;
-- test parallel plans for queries containing un-correlated subplans.
alter table tenk2 set (parallel_workers = 0);
explain (costs off)
select count(*) from tenk1 where (two, four) not in
(select hundred, thousand from tenk2 where thousand > 100);
QUERY PLAN
------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Seq Scan on tenk1
Filter: (NOT (hashed SubPlan 1))
SubPlan 1
-> Seq Scan on tenk2
Filter: (thousand > 100)
(9 rows)
select count(*) from tenk1 where (two, four) not in
(select hundred, thousand from tenk2 where thousand > 100);
count
-------
10000
(1 row)
-- this is not parallel-safe due to use of random() within SubLink's testexpr:
explain (costs off)
select * from tenk1 where (unique1 + random())::integer not in
(select ten from tenk2);
QUERY PLAN
------------------------------------
Seq Scan on tenk1
Filter: (NOT (hashed SubPlan 1))
SubPlan 1
-> Seq Scan on tenk2
(4 rows)
alter table tenk2 reset (parallel_workers);
-- test parallel plan for a query containing initplan.
set enable_indexscan = off;
set enable_indexonlyscan = off;
set enable_bitmapscan = off;
alter table tenk2 set (parallel_workers = 2);
explain (costs off)
select count(*) from tenk1
where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
QUERY PLAN
------------------------------------------------------
Aggregate
InitPlan 1 (returns $2)
-> Finalize Aggregate
-> Gather
Workers Planned: 2
-> Partial Aggregate
-> Parallel Seq Scan on tenk2
-> Gather
Workers Planned: 4
Params Evaluated: $2
-> Parallel Seq Scan on tenk1
Filter: (unique1 = $2)
(12 rows)
select count(*) from tenk1
where tenk1.unique1 = (Select max(tenk2.unique1) from tenk2);
count
-------
1
(1 row)
reset enable_indexscan;
reset enable_indexonlyscan;
reset enable_bitmapscan;
alter table tenk2 reset (parallel_workers);
-- test parallel index scans.
set enable_seqscan to off;
set enable_bitmapscan to off;
explain (costs off)
select count((unique1)) from tenk1 where hundred > 1;
QUERY PLAN
--------------------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Index Scan using tenk1_hundred on tenk1
Index Cond: (hundred > 1)
(6 rows)
select count((unique1)) from tenk1 where hundred > 1;
count
-------
9800
(1 row)
-- test parallel index-only scans.
explain (costs off)
select count(*) from tenk1 where thousand > 95;
QUERY PLAN
--------------------------------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Index Only Scan using tenk1_thous_tenthous on tenk1
Index Cond: (thousand > 95)
(6 rows)
select count(*) from tenk1 where thousand > 95;
count
-------
9040
(1 row)
-- test rescan cases too
set enable_material = false;
explain (costs off)
select * from
(select count(unique1) from tenk1 where hundred > 10) ss
right join (values (1),(2),(3)) v(x) on true;
QUERY PLAN
--------------------------------------------------------------------------
Nested Loop Left Join
-> Values Scan on "*VALUES*"
-> Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Index Scan using tenk1_hundred on tenk1
Index Cond: (hundred > 10)
(8 rows)
select * from
(select count(unique1) from tenk1 where hundred > 10) ss
right join (values (1),(2),(3)) v(x) on true;
count | x
-------+---
8900 | 1
8900 | 2
8900 | 3
(3 rows)
explain (costs off)
select * from
(select count(*) from tenk1 where thousand > 99) ss
right join (values (1),(2),(3)) v(x) on true;
QUERY PLAN
--------------------------------------------------------------------------------------
Nested Loop Left Join
-> Values Scan on "*VALUES*"
-> Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Index Only Scan using tenk1_thous_tenthous on tenk1
Index Cond: (thousand > 99)
(8 rows)
select * from
(select count(*) from tenk1 where thousand > 99) ss
right join (values (1),(2),(3)) v(x) on true;
count | x
-------+---
9000 | 1
9000 | 2
9000 | 3
(3 rows)
reset enable_material;
reset enable_seqscan;
reset enable_bitmapscan;
-- test parallel bitmap heap scan.
set enable_seqscan to off;
set enable_indexscan to off;
set enable_hashjoin to off;
set enable_mergejoin to off;
set enable_material to off;
-- test prefetching, if the platform allows it
DO $$
BEGIN
SET effective_io_concurrency = 50;
EXCEPTION WHEN invalid_parameter_value THEN
END $$;
set work_mem='64kB'; --set small work mem to force lossy pages
explain (costs off)
select count(*) from tenk1, tenk2 where tenk1.hundred > 1 and tenk2.thousand=0;
QUERY PLAN
------------------------------------------------------------
Aggregate
-> Nested Loop
-> Seq Scan on tenk2
Filter: (thousand = 0)
-> Gather
Workers Planned: 4
-> Parallel Bitmap Heap Scan on tenk1
Recheck Cond: (hundred > 1)
-> Bitmap Index Scan on tenk1_hundred
Index Cond: (hundred > 1)
(10 rows)
select count(*) from tenk1, tenk2 where tenk1.hundred > 1 and tenk2.thousand=0;
count
-------
98000
(1 row)
create table bmscantest (a int, t text);
insert into bmscantest select r, 'fooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo' FROM generate_series(1,100000) r;
create index i_bmtest ON bmscantest(a);
select count(*) from bmscantest where a>1;
count
-------
99999
(1 row)
-- test accumulation of stats for parallel nodes
reset enable_seqscan;
alter table tenk2 set (parallel_workers = 0);
explain (analyze, timing off, summary off, costs off)
select count(*) from tenk1, tenk2 where tenk1.hundred > 1
and tenk2.thousand=0;
QUERY PLAN
--------------------------------------------------------------------------
Aggregate (actual rows=1 loops=1)
-> Nested Loop (actual rows=98000 loops=1)
-> Seq Scan on tenk2 (actual rows=10 loops=1)
Filter: (thousand = 0)
Rows Removed by Filter: 9990
-> Gather (actual rows=9800 loops=10)
Workers Planned: 4
Workers Launched: 4
-> Parallel Seq Scan on tenk1 (actual rows=1960 loops=50)
Filter: (hundred > 1)
Rows Removed by Filter: 40
(11 rows)
alter table tenk2 reset (parallel_workers);
reset work_mem;
create function explain_parallel_sort_stats() returns setof text
language plpgsql as
$$
declare ln text;
begin
for ln in
explain (analyze, timing off, summary off, costs off)
select * from
(select ten from tenk1 where ten < 100 order by ten) ss
right join (values (1),(2),(3)) v(x) on true
loop
ln := regexp_replace(ln, 'Memory: \S*', 'Memory: xxx');
return next ln;
end loop;
end;
$$;
select * from explain_parallel_sort_stats();
explain_parallel_sort_stats
--------------------------------------------------------------------------
Nested Loop Left Join (actual rows=30000 loops=1)
-> Values Scan on "*VALUES*" (actual rows=3 loops=1)
-> Gather Merge (actual rows=10000 loops=3)
Workers Planned: 4
Workers Launched: 4
-> Sort (actual rows=2000 loops=15)
Sort Key: tenk1.ten
Sort Method: quicksort Memory: xxx
Worker 0: Sort Method: quicksort Memory: xxx
Worker 1: Sort Method: quicksort Memory: xxx
Worker 2: Sort Method: quicksort Memory: xxx
Worker 3: Sort Method: quicksort Memory: xxx
-> Parallel Seq Scan on tenk1 (actual rows=2000 loops=15)
Filter: (ten < 100)
(14 rows)
reset enable_indexscan;
reset enable_hashjoin;
reset enable_mergejoin;
reset enable_material;
reset effective_io_concurrency;
drop table bmscantest;
drop function explain_parallel_sort_stats();
-- test parallel merge join path.
set enable_hashjoin to off;
set enable_nestloop to off;
explain (costs off)
select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1;
QUERY PLAN
-------------------------------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Merge Join
Merge Cond: (tenk1.unique1 = tenk2.unique1)
-> Parallel Index Only Scan using tenk1_unique1 on tenk1
-> Index Only Scan using tenk2_unique1 on tenk2
(8 rows)
select count(*) from tenk1, tenk2 where tenk1.unique1 = tenk2.unique1;
count
-------
10000
(1 row)
reset enable_hashjoin;
reset enable_nestloop;
-- test gather merge
set enable_hashagg = false;
explain (costs off)
select count(*) from tenk1 group by twenty;
QUERY PLAN
----------------------------------------------------
Finalize GroupAggregate
Group Key: twenty
-> Gather Merge
Workers Planned: 4
-> Partial GroupAggregate
Group Key: twenty
-> Sort
Sort Key: twenty
-> Parallel Seq Scan on tenk1
(9 rows)
select count(*) from tenk1 group by twenty;
count
-------
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
(20 rows)
--test expressions in targetlist are pushed down for gather merge
create function sp_simple_func(var1 integer) returns integer
as $$
begin
return var1 + 10;
end;
$$ language plpgsql PARALLEL SAFE;
explain (costs off, verbose)
select ten, sp_simple_func(ten) from tenk1 where ten < 100 order by ten;
QUERY PLAN
-----------------------------------------------------
Gather Merge
Output: ten, (sp_simple_func(ten))
Workers Planned: 4
-> Result
Output: ten, sp_simple_func(ten)
-> Sort
Output: ten
Sort Key: tenk1.ten
-> Parallel Seq Scan on public.tenk1
Output: ten
Filter: (tenk1.ten < 100)
(11 rows)
drop function sp_simple_func(integer);
-- test gather merge with parallel leader participation disabled
set parallel_leader_participation = off;
explain (costs off)
select count(*) from tenk1 group by twenty;
QUERY PLAN
----------------------------------------------------
Finalize GroupAggregate
Group Key: twenty
-> Gather Merge
Workers Planned: 4
-> Partial GroupAggregate
Group Key: twenty
-> Sort
Sort Key: twenty
-> Parallel Seq Scan on tenk1
(9 rows)
select count(*) from tenk1 group by twenty;
count
-------
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
500
(20 rows)
reset parallel_leader_participation;
--test rescan behavior of gather merge
set enable_material = false;
explain (costs off)
select * from
(select string4, count(unique2)
from tenk1 group by string4 order by string4) ss
right join (values (1),(2),(3)) v(x) on true;
QUERY PLAN
----------------------------------------------------------
Nested Loop Left Join
-> Values Scan on "*VALUES*"
-> Finalize GroupAggregate
Group Key: tenk1.string4
-> Gather Merge
Workers Planned: 4
-> Partial GroupAggregate
Group Key: tenk1.string4
-> Sort
Sort Key: tenk1.string4
-> Parallel Seq Scan on tenk1
(11 rows)
select * from
(select string4, count(unique2)
from tenk1 group by string4 order by string4) ss
right join (values (1),(2),(3)) v(x) on true;
string4 | count | x
---------+-------+---
AAAAxx | 2500 | 1
HHHHxx | 2500 | 1
OOOOxx | 2500 | 1
VVVVxx | 2500 | 1
AAAAxx | 2500 | 2
HHHHxx | 2500 | 2
OOOOxx | 2500 | 2
VVVVxx | 2500 | 2
AAAAxx | 2500 | 3
HHHHxx | 2500 | 3
OOOOxx | 2500 | 3
VVVVxx | 2500 | 3
(12 rows)
reset enable_material;
reset enable_hashagg;
-- check parallelized int8 aggregate (bug #14897)
explain (costs off)
select avg(unique1::int8) from tenk1;
QUERY PLAN
-------------------------------------------------------------------------
Finalize Aggregate
-> Gather
Workers Planned: 4
-> Partial Aggregate
-> Parallel Index Only Scan using tenk1_unique1 on tenk1
(5 rows)
select avg(unique1::int8) from tenk1;
avg
-----------------------
4999.5000000000000000
(1 row)
-- gather merge test with a LIMIT
explain (costs off)
select fivethous from tenk1 order by fivethous limit 4;
QUERY PLAN
----------------------------------------------
Limit
-> Gather Merge
Workers Planned: 4
-> Sort
Sort Key: fivethous
-> Parallel Seq Scan on tenk1
(6 rows)
select fivethous from tenk1 order by fivethous limit 4;
fivethous
-----------
0
0
1
1
(4 rows)
-- gather merge test with 0 worker
set max_parallel_workers = 0;
explain (costs off)
select string4 from tenk1 order by string4 limit 5;
QUERY PLAN
----------------------------------------------
Limit
-> Gather Merge
Workers Planned: 4
-> Sort
Sort Key: string4
-> Parallel Seq Scan on tenk1
(6 rows)
select string4 from tenk1 order by string4 limit 5;
string4
---------
AAAAxx
AAAAxx
AAAAxx
AAAAxx
AAAAxx
(5 rows)
-- gather merge test with 0 workers, with parallel leader
-- participation disabled (the leader will have to run the plan
-- despite the setting)
set parallel_leader_participation = off;
explain (costs off)
select string4 from tenk1 order by string4 limit 5;
QUERY PLAN
----------------------------------------------
Limit
-> Gather Merge
Workers Planned: 4
-> Sort
Sort Key: string4
-> Parallel Seq Scan on tenk1
(6 rows)
select string4 from tenk1 order by string4 limit 5;
string4
---------
AAAAxx
AAAAxx
AAAAxx
AAAAxx
AAAAxx
(5 rows)
reset parallel_leader_participation;
reset max_parallel_workers;
SAVEPOINT settings;
SET LOCAL force_parallel_mode = 1;
explain (costs off)
select stringu1::int2 from tenk1 where unique1 = 1;
QUERY PLAN
-----------------------------------------------
Gather
Workers Planned: 1
Single Copy: true
-> Index Scan using tenk1_unique1 on tenk1
Index Cond: (unique1 = 1)
(5 rows)
ROLLBACK TO SAVEPOINT settings;
-- exercise record typmod remapping between backends
CREATE FUNCTION make_record(n int)
RETURNS RECORD LANGUAGE plpgsql PARALLEL SAFE AS
$$
BEGIN
RETURN CASE n
WHEN 1 THEN ROW(1)
WHEN 2 THEN ROW(1, 2)
WHEN 3 THEN ROW(1, 2, 3)
WHEN 4 THEN ROW(1, 2, 3, 4)
ELSE ROW(1, 2, 3, 4, 5)
END;
END;
$$;
SAVEPOINT settings;
SET LOCAL force_parallel_mode = 1;
SELECT make_record(x) FROM (SELECT generate_series(1, 5) x) ss ORDER BY x;
make_record
-------------
(1)
(1,2)
(1,2,3)
(1,2,3,4)
(1,2,3,4,5)
(5 rows)
ROLLBACK TO SAVEPOINT settings;
DROP function make_record(n int);
-- test the sanity of parallel query after the active role is dropped.
drop role if exists regress_parallel_worker;
NOTICE: role "regress_parallel_worker" does not exist, skipping
create role regress_parallel_worker;
set role regress_parallel_worker;
reset session authorization;
drop role regress_parallel_worker;
set force_parallel_mode = 1;
select count(*) from tenk1;
count
-------
10000
(1 row)
reset force_parallel_mode;
reset role;
-- to increase the parallel query test coverage
SAVEPOINT settings;
SET LOCAL force_parallel_mode = 1;
EXPLAIN (analyze, timing off, summary off, costs off) SELECT * FROM tenk1;
QUERY PLAN
-------------------------------------------------------------
Gather (actual rows=10000 loops=1)
Workers Planned: 4
Workers Launched: 4
-> Parallel Seq Scan on tenk1 (actual rows=2000 loops=5)
(4 rows)
ROLLBACK TO SAVEPOINT settings;
-- provoke error in worker
SAVEPOINT settings;
SET LOCAL force_parallel_mode = 1;
select stringu1::int2 from tenk1 where unique1 = 1;
ERROR: invalid input syntax for integer: "BAAAAA"
CONTEXT: parallel worker
ROLLBACK TO SAVEPOINT settings;
-- test interaction with set-returning functions
SAVEPOINT settings;
-- multiple subqueries under a single Gather node
-- must set parallel_setup_cost > 0 to discourage multiple Gather nodes
SET LOCAL parallel_setup_cost = 10;
EXPLAIN (COSTS OFF)
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1
UNION ALL
SELECT unique1 FROM tenk1 WHERE fivethous = tenthous + 1;
QUERY PLAN
----------------------------------------------------
Gather
Workers Planned: 4
-> Parallel Append
-> Parallel Seq Scan on tenk1
Filter: (fivethous = (tenthous + 1))
-> Parallel Seq Scan on tenk1 tenk1_1
Filter: (fivethous = (tenthous + 1))
(7 rows)
ROLLBACK TO SAVEPOINT settings;
-- can't use multiple subqueries under a single Gather node due to initPlans
EXPLAIN (COSTS OFF)
SELECT unique1 FROM tenk1 WHERE fivethous =
(SELECT unique1 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
UNION ALL
SELECT unique1 FROM tenk1 WHERE fivethous =
(SELECT unique2 FROM tenk1 WHERE fivethous = 1 LIMIT 1)
ORDER BY 1;
QUERY PLAN
--------------------------------------------------------------------
Sort
Sort Key: tenk1.unique1
-> Append
-> Gather
Workers Planned: 4
Params Evaluated: $1
InitPlan 1 (returns $1)
-> Limit
-> Gather
Workers Planned: 4
-> Parallel Seq Scan on tenk1 tenk1_2
Filter: (fivethous = 1)
-> Parallel Seq Scan on tenk1
Filter: (fivethous = $1)
-> Gather
Workers Planned: 4
Params Evaluated: $3
InitPlan 2 (returns $3)
-> Limit
-> Gather
Workers Planned: 4
-> Parallel Seq Scan on tenk1 tenk1_3
Filter: (fivethous = 1)
-> Parallel Seq Scan on tenk1 tenk1_1
Filter: (fivethous = $3)
(25 rows)
-- test interaction with SRFs
SELECT * FROM information_schema.foreign_data_wrapper_options
ORDER BY 1, 2, 3;
foreign_data_wrapper_catalog | foreign_data_wrapper_name | option_name | option_value
------------------------------+---------------------------+-------------+--------------
(0 rows)
rollback;
|