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Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.

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WHERE EXISTS (...) queries cannot be executed by Parallel Hash Join
with jointype JOIN_UNIQUE_INNER, because there is no way to make a
partial plan totally unique.  The consequence of allowing such plans
was duplicate results from some EXISTS queries.

Back-patch to 11.  Bug #15857.

Author: Thomas Munro
Reviewed-by: Tom Lane
Reported-by: Vladimir Kriukov
Discussion: https://postgr.es/m/15857-d1ba2a64bce0795e%40postgresql.org
This commit is contained in:
Thomas Munro 2019-06-18 22:38:30 +12:00
parent e5f26d79ba
commit 14d8b539d3
1 changed files with 5 additions and 2 deletions
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7
src/backend/optimizer/path/joinpath.c
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@ -1867,9 +1867,12 @@ hash_inner_and_outer(PlannerInfo *root,
/*
* Can we use a partial inner plan too, so that we can build a
* shared hash table in parallel?
* shared hash table in parallel? We can't handle
* JOIN_UNIQUE_INNER because we can't guarantee uniqueness.
*/
if (innerrel->partial_pathlist != NIL && enable_parallel_hash)
if (innerrel->partial_pathlist != NIL &&
save_jointype != JOIN_UNIQUE_INNER &&
enable_parallel_hash)
{
cheapest_partial_inner =
(Path *) linitial(innerrel->partial_pathlist);