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Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.

Thomas Munro <tmunro@postgresql.org>

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Commit: aca127c105aae551620d607e88d76930e6b9a2cf
Author: Thomas Munro <tmunro@postgresql.org>
Date: 2019-06-18T13:25:57Z
Releases: 12.0 
Prevent Parallel Hash Join for JOIN_UNIQUE_INNER.

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

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PathChange+/−
src/backend/optimizer/path/joinpath.c modified +5 −2

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