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Fix generation of EC join conditions at the wrong plan level.

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get_baserel_parampathinfo previously assumed without checking that
the results of generate_join_implied_equalities "necessarily satisfy
join_clause_is_movable_into".  This turns out to be wrong in the
presence of outer joins, because the generated clauses could include
Vars that mustn't be evaluated below a relevant outer join.  That
led to applying clauses at the wrong plan level and possibly getting
incorrect query results.  We must check each clause's nullable_relids,
and really the right thing to do is test join_clause_is_movable_into.

However, trying to fix it that way exposes an oversight in
equivclass.c: it wasn't careful about marking join clauses for
appendrel children with the correct clause_relids.  That caused the
modified get_baserel_parampathinfo code to reject some clauses it
still needs to accept.  (See parallel commit for HEAD/v16 for more
commentary about that.)

Per bug #18429 from Benoît Ryder.  This misbehavior existed for
a long time before commit 2489d76c4, so patch v12-v15 this way.

Discussion: https://postgr.es/m/18429-8982d4a348cc86c6@postgresql.org
This commit is contained in:
Tom Lane
2024-04-16 11:22:39 -04:00
parent 4b0e5d6012
commit f502849d49
4 changed files with 83 additions and 7 deletions
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25
src/backend/optimizer/util/relnode.c
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@ -1264,6 +1264,7 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
ParamPathInfo *ppi;
Relids joinrelids;
List *pclauses;
List *eqclauses;
double rows;
ListCell *lc;
@ -1297,14 +1298,24 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
}
/*
* Add in joinclauses generated by EquivalenceClasses, too. (These
* necessarily satisfy join_clause_is_movable_into.)
* Add in joinclauses generated by EquivalenceClasses, too. In principle
* these should always satisfy join_clause_is_movable_into; but if we are
* below an outer join the clauses might contain Vars that should only be
* evaluated above the join, so we have to check.
*/
pclauses = list_concat(pclauses,
generate_join_implied_equalities(root,
joinrelids,
required_outer,
baserel));
eqclauses = generate_join_implied_equalities(root,
joinrelids,
required_outer,
baserel);
foreach(lc, eqclauses)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
if (join_clause_is_movable_into(rinfo,
baserel->relids,
joinrelids))
pclauses = lappend(pclauses, rinfo);
}
/* Estimate the number of rows returned by the parameterized scan */
rows = get_parameterized_baserel_size(root, baserel, pclauses);