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Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.

WHERE EXISTS (...) queries cannot be executed by Parallel Hash Joinwith jointype JOIN_UNIQUE_INNER, because there is no way to make apartial plan totally unique. The consequence of allowing such planswas duplicate results from some EXISTS queries.Back-patch to 11. Bug #15857.Author: Thomas MunroReviewed-by: Tom LaneReported-by: Vladimir KriukovDiscussion:https://postgr.es/m/15857-d1ba2a64bce0795e%40postgresql.org

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src/backend/optimizer/path
- joinpath.c

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`‎src/backend/optimizer/path/joinpath.c`

Lines changed: 5 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -1867,9 +1867,12 @@ hash_inner_and_outer(PlannerInfo *root,`
`1867`	`1867`
`1868`	`1868`	`/*`
`1869`	`1869`	`* Can we use a partial inner plan too, so that we can build a`
`1870`		`- * shared hash table in parallel?`
	`1870`	`+ * shared hash table in parallel? We can't handle`
	`1871`	`+ * JOIN_UNIQUE_INNER because we can't guarantee uniqueness.`
`1871`	`1872`	`*/`
`1872`		`-if (innerrel->partial_pathlist!=NIL&&enable_parallel_hash)`
	`1873`	`+if (innerrel->partial_pathlist!=NIL&&`
	`1874`	`+save_jointype!=JOIN_UNIQUE_INNER&&`
	`1875`	`+enable_parallel_hash)`
`1873`	`1876`	`{`
`1874`	`1877`	`cheapest_partial_inner=`
`1875`	`1878`	`(Path*)linitial(innerrel->partial_pathlist);`

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`‎src/backend/optimizer/path/joinpath.c`

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