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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2020-07-13 20:38:20 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2020-07-13 20:38:20 -0400 |
| commit | a742ecf9c63d454ccb107a357288c8ec1444ca12 (patch) | |
| tree | 13a753cfcc6535c48ce92cac17d28d7edec17b29 /src/backend/optimizer/path/allpaths.c | |
| parent | b5b4c0fef9fb905d98f93c1f455397449c6e63a8 (diff) | |
| download | postgresql-a742ecf9c63d454ccb107a357288c8ec1444ca12.tar.gz postgresql-a742ecf9c63d454ccb107a357288c8ec1444ca12.zip | |
Cope with lateral references in the quals of a subquery RTE.
The qual pushdown logic assumed that all Vars in a restriction clause
must be Vars referencing subquery outputs; but since we introduced
LATERAL, it's possible for such a Var to be a lateral reference instead.
This led to an assertion failure in debug builds. In a non-debug
build, there might be no ill effects (if qual_is_pushdown_safe decided
the qual was unsafe anyway), or we could get failures later due to
construction of an invalid plan. I've not gone to much length to
characterize the possible failures, but at least segfaults in the
executor have been observed.
Given that this has been busted since 9.3 and it took this long for
anybody to notice, I judge that the case isn't worth going to great
lengths to optimize. Hence, fix by just teaching qual_is_pushdown_safe
that such quals are unsafe to push down, matching the previous behavior
when it accidentally didn't fail.
Per report from Tom Ellis. Back-patch to all supported branches.
Discussion: https://postgr.es/m/20200713175124.GQ8220@cloudinit-builder
Diffstat (limited to 'src/backend/optimizer/path/allpaths.c')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index c4e1967f123..6da0dcd61ce 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -3508,8 +3508,10 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual, Assert(!contain_window_function(qual)); /* - * Examine all Vars used in clause; since it's a restriction clause, all - * such Vars must refer to subselect output columns. + * Examine all Vars used in clause. Since it's a restriction clause, all + * such Vars must refer to subselect output columns ... unless this is + * part of a LATERAL subquery, in which case there could be lateral + * references. */ vars = pull_var_clause(qual, PVC_INCLUDE_PLACEHOLDERS); foreach(vl, vars) @@ -3529,7 +3531,19 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual, break; } - Assert(var->varno == rti); + /* + * Punt if we find any lateral references. It would be safe to push + * these down, but we'd have to convert them into outer references, + * which subquery_push_qual lacks the infrastructure to do. The case + * arises so seldom that it doesn't seem worth working hard on. + */ + if (var->varno != rti) + { + safe = false; + break; + } + + /* Subqueries have no system columns */ Assert(var->varattno >= 0); /* Check point 4 */ |