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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 allunderlying tuples.Use explain without analyze to avoid such a problem. As I see, we don't loseanything important.

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expected
- parallel_workers.out
sql
- parallel_workers.sql

2 files changed

+20

-22

lines changed

`‎expected/parallel_workers.out`

Lines changed: 18 additions & 19 deletions

Original file line number	Diff line number	Diff line change
`@@ -68,53 +68,52 @@ WHERE q1.id = q2.id; -- Learning stage`
`68`	`68`
`69`	`69`	`-- XXX: Why grouping prediction isn't working here?`
`70`	`70`	`SELECT str FROM expln('`
`71`		`-EXPLAIN (ANALYZE,COSTS OFF, TIMING OFF, SUMMARY OFF)`
	`71`	`+EXPLAIN (COSTS OFF, TIMING OFF, SUMMARY OFF)`
`72`	`72`	`SELECT count(*) FROM`
`73`	`73`	`(SELECT id FROM t WHERE id % 100 = 0 GROUP BY (id)) AS q1,`
`74`	`74`	`(SELECT max(id) AS id, payload FROM t`
`75`	`75`	`WHERE id % 101 = 0 GROUP BY (payload)) AS q2`
`76`	`76`	`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%';`
`79`	`78`	`str`
`80`	`79`	`--------------------------------------------------------------------------------------------------`
`81`		`- Aggregate (actual rows=1 loops=1)`
	`80`	`+ Aggregate`
`82`	`81`	`AQO not used`
`83`		`- -> Merge Join (actual rows=0 loops=1)`
	`82`	`+ -> Merge Join`
`84`	`83`	`AQO not used`
`85`	`84`	`Merge Cond: (q2.id = t_1.id)`
`86`		`- -> Sort (actual rows=1 loops=1)`
	`85`	`+ -> Sort`
`87`	`86`	`Sort Key: q2.id`
`88`		`- -> Subquery Scan on q2 (actual rows=1 loops=1)`
	`87`	`+ -> Subquery Scan on q2`
`89`	`88`	`AQO not used`
`90`		`- -> Finalize GroupAggregate (actual rows=1 loops=1)`
	`89`	`+ -> Finalize GroupAggregate`
`91`	`90`	`AQO not used`
`92`	`91`	`Group Key: t.payload`
	`92`	`+ -> Gather Merge`
`93`	`93`	`AQO not used`
`94`		`- -> Partial GroupAggregate (actual rows=1 loops=3)`
	`94`	`+ -> Partial GroupAggregate`
`95`	`95`	`AQO not used`
`96`	`96`	`Group Key: t.payload`
`97`		`- -> Sort (actual rows=330 loops=3)`
	`97`	`+ -> Sort`
`98`	`98`	`AQO not used`
`99`	`99`	`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`
`102`	`102`	`Filter: ((id % '101'::numeric) = '0'::numeric)`
`103`		`- Rows Removed by Filter: 33003`
`104`		`- -> Group (actual rows=1000 loops=1)`
	`103`	`+ -> Group`
`105`	`104`	`AQO not used`
`106`	`105`	`Group Key: t_1.id`
	`106`	`+ -> Gather Merge`
`107`	`107`	`AQO not used`
`108`		`- -> Group (actual rows=333 loops=3)`
	`108`	`+ -> Group`
`109`	`109`	`AQO not used`
`110`	`110`	`Group Key: t_1.id`
`111`		`- -> Sort (actual rows=333 loops=3)`
	`111`	`+ -> Sort`
`112`	`112`	`AQO not used`
`113`	`113`	`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`
`116`	`116`	`Filter: ((id % '100'::numeric) = '0'::numeric)`
`117`		`- Rows Removed by Filter: 33000`
`118`	`117`	`Using aqo: true`
`119`	`118`	`AQO mode: LEARN`
`120`	`119`	`JOINS: 1`

`‎sql/parallel_workers.sql`

Lines changed: 2 additions & 3 deletions

Original file line number	Diff line number	Diff line change
`@@ -43,14 +43,13 @@ SELECT count(*) FROM`
`43`	`43`	`WHEREq1.id=q2.id;-- Learning stage`
`44`	`44`	`-- XXX: Why grouping prediction isn't working here?`
`45`	`45`	`SELECT strFROM expln('`
`46`		`-EXPLAIN (ANALYZE,COSTS OFF, TIMING OFF, SUMMARY OFF)`
	`46`	`+EXPLAIN (COSTS OFF, TIMING OFF, SUMMARY OFF)`
`47`	`47`	`SELECT count(*) FROM`
`48`	`48`	`(SELECT id FROM t WHERE id % 100 = 0 GROUP BY (id)) AS q1,`
`49`	`49`	`(SELECT max(id) AS id, payload FROM t`
`50`	`50`	`WHERE id % 101 = 0 GROUP BY (payload)) AS q2`
`51`	`51`	`WHERE q1.id = q2.id;')AS str`
`52`		`-WHERE str NOTLIKE'%Workers%'AND str NOTLIKE'%Sort Method%'`
`53`		`-AND str NOTLIKE'%Gather Merge%';`
	`52`	`+WHERE str NOTLIKE'%Workers%';`
`54`	`53`
`55`	`54`	`RESET parallel_tuple_cost;`
`56`	`55`	`RESET parallel_setup_cost;`

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Commitefff724

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`‎expected/parallel_workers.out`

`‎sql/parallel_workers.sql`

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