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Commit efff724

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Enhancement. Buildfarm have detected curious unstability in the parallel_workers
test: EXPLAIN of Partial Aggregate sometimes showed 0 rows instead 1. It is a race: parallel workers ran when main process have read all underlying tuples. Use explain without analyze to avoid such a problem. As I see, we don't lose anything important.
1 parent 1b33907 commit efff724

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2 files changed

+20
-22
lines changed

2 files changed

+20
-22
lines changed

‎expected/parallel_workers.out‎

Lines changed: 18 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -68,53 +68,52 @@ WHERE q1.id = q2.id; -- Learning stage
6868

6969
-- XXX: Why grouping prediction isn't working here?
7070
SELECT str FROM expln('
71-
EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF, SUMMARY OFF)
71+
EXPLAIN (COSTS OFF, TIMING OFF, SUMMARY OFF)
7272
SELECT count(*) FROM
7373
(SELECT id FROM t WHERE id % 100 = 0 GROUP BY (id)) AS q1,
7474
(SELECT max(id) AS id, payload FROM t
7575
WHERE id % 101 = 0 GROUP BY (payload)) AS q2
7676
WHERE q1.id = q2.id;') AS str
77-
WHERE str NOT LIKE '%Workers%' AND str NOT LIKE '%Sort Method%'
78-
AND str NOT LIKE '%Gather Merge%';
77+
WHERE str NOT LIKE '%Workers%';
7978
str
8079
--------------------------------------------------------------------------------------------------
81-
Aggregate (actual rows=1 loops=1)
80+
Aggregate
8281
AQO not used
83-
-> Merge Join (actual rows=0 loops=1)
82+
-> Merge Join
8483
AQO not used
8584
Merge Cond: (q2.id = t_1.id)
86-
-> Sort (actual rows=1 loops=1)
85+
-> Sort
8786
Sort Key: q2.id
88-
-> Subquery Scan on q2 (actual rows=1 loops=1)
87+
-> Subquery Scan on q2
8988
AQO not used
90-
-> Finalize GroupAggregate (actual rows=1 loops=1)
89+
-> Finalize GroupAggregate
9190
AQO not used
9291
Group Key: t.payload
92+
-> Gather Merge
9393
AQO not used
94-
-> Partial GroupAggregate (actual rows=1 loops=3)
94+
-> Partial GroupAggregate
9595
AQO not used
9696
Group Key: t.payload
97-
-> Sort (actual rows=330 loops=3)
97+
-> Sort
9898
AQO not used
9999
Sort Key: t.payload
100-
-> Parallel Seq Scan on t (actual rows=330 loops=3)
101-
AQO: rows=991, error=0%
100+
-> Parallel Seq Scan on t
101+
AQO: rows=991
102102
Filter: ((id % '101'::numeric) = '0'::numeric)
103-
Rows Removed by Filter: 33003
104-
-> Group (actual rows=1000 loops=1)
103+
-> Group
105104
AQO not used
106105
Group Key: t_1.id
106+
-> Gather Merge
107107
AQO not used
108-
-> Group (actual rows=333 loops=3)
108+
-> Group
109109
AQO not used
110110
Group Key: t_1.id
111-
-> Sort (actual rows=333 loops=3)
111+
-> Sort
112112
AQO not used
113113
Sort Key: t_1.id
114-
-> Parallel Seq Scan on t t_1 (actual rows=333 loops=3)
115-
AQO: rows=991, error=-1%
114+
-> Parallel Seq Scan on t t_1
115+
AQO: rows=991
116116
Filter: ((id % '100'::numeric) = '0'::numeric)
117-
Rows Removed by Filter: 33000
118117
Using aqo: true
119118
AQO mode: LEARN
120119
JOINS: 1

‎sql/parallel_workers.sql‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -43,14 +43,13 @@ SELECT count(*) FROM
4343
WHERE q1.id = q2.id; -- Learning stage
4444
-- XXX: Why grouping prediction isn't working here?
4545
SELECT str FROM expln('
46-
EXPLAIN (ANALYZE, COSTS OFF, TIMING OFF, SUMMARY OFF)
46+
EXPLAIN (COSTS OFF, TIMING OFF, SUMMARY OFF)
4747
SELECT count(*) FROM
4848
(SELECT id FROM t WHERE id % 100 = 0 GROUP BY (id)) AS q1,
4949
(SELECT max(id) AS id, payload FROM t
5050
WHERE id % 101 = 0 GROUP BY (payload)) AS q2
5151
WHERE q1.id = q2.id;') AS str
52-
WHERE str NOT LIKE '%Workers%' AND str NOT LIKE '%Sort Method%'
53-
AND str NOT LIKE '%Gather Merge%';
52+
WHERE str NOT LIKE '%Workers%';
5453

5554
RESET parallel_tuple_cost;
5655
RESET parallel_setup_cost;

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