From aca127c105aae551620d607e88d76930e6b9a2cf Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Tue, 18 Jun 2019 22:38:30 +1200 Subject: [PATCH] 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 --- src/backend/optimizer/path/joinpath.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 501ad775cb..dc28b56e74 100644 --- a/src/backend/optimizer/path/joinpath.c +++ b/src/backend/optimizer/path/joinpath.c @@ -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);