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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2017-05-01 14:39:11 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2017-05-01 14:39:11 -0400 |
| commit | 2057a58d1629ebffce694e3cef7f714571a88dd7 (patch) | |
| tree | d96a4bc525cc403668ae5984fe940a719639e83b /src/backend/optimizer/path/joinpath.c | |
| parent | 74a20d0ab7c99b3efcf5dc7aac741e3b2f952a34 (diff) | |
| download | postgresql-2057a58d1629ebffce694e3cef7f714571a88dd7.tar.gz postgresql-2057a58d1629ebffce694e3cef7f714571a88dd7.zip | |
Fix mis-optimization of semijoins with more than one LHS relation.
The inner-unique patch (commit 9c7f5229a) supposed that if we're
considering a JOIN_UNIQUE_INNER join path, we can always set inner_unique
for the join, because the inner path produced by create_unique_path should
be unique relative to the outer relation. However, that's true only if
we're considering joining to the whole outer relation --- otherwise we may
be applying only some of the join quals, and so the inner path might be
non-unique from the perspective of this join. Adjust the test to only
believe that we can set inner_unique if we have the whole semijoin LHS on
the outer side.
There is more that can be done in this area, but this commit is only
intended to provide the minimal fix needed to get correct plans.
Per report from Teodor Sigaev. Thanks to David Rowley for preliminary
investigation.
Discussion: https://postgr.es/m/f994fc98-389f-4a46-d1bc-c42e05cb43ed@sigaev.ru
Diffstat (limited to 'src/backend/optimizer/path/joinpath.c')
| -rw-r--r-- | src/backend/optimizer/path/joinpath.c | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c index 5aedcd15411..39e2ddda906 100644 --- a/src/backend/optimizer/path/joinpath.c +++ b/src/backend/optimizer/path/joinpath.c @@ -126,8 +126,11 @@ add_paths_to_joinrel(PlannerInfo *root, * * We have some special cases: for JOIN_SEMI and JOIN_ANTI, it doesn't * matter since the executor can make the equivalent optimization anyway; - * we need not expend planner cycles on proofs. For JOIN_UNIQUE_INNER, we - * know we're going to force uniqueness of the innerrel below. For + * we need not expend planner cycles on proofs. For JOIN_UNIQUE_INNER, if + * the LHS covers all of the associated semijoin's min_lefthand, then it's + * appropriate to set inner_unique because the path produced by + * create_unique_path will be unique relative to the LHS. (If we have an + * LHS that's only part of the min_lefthand, that is *not* true.) For * JOIN_UNIQUE_OUTER, pass JOIN_INNER to avoid letting that value escape * this module. */ @@ -138,7 +141,8 @@ add_paths_to_joinrel(PlannerInfo *root, extra.inner_unique = false; /* well, unproven */ break; case JOIN_UNIQUE_INNER: - extra.inner_unique = true; + extra.inner_unique = bms_is_subset(sjinfo->min_lefthand, + outerrel->relids); break; case JOIN_UNIQUE_OUTER: extra.inner_unique = innerrel_is_unique(root, outerrel, innerrel, |