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Check parallel safety in generate_useful_gather_paths

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Commit ebb7ae839d ensured we ignore pathkeys with volatile expressions
when considering adding a sort below a Gather Merge. Turns out we need
to care about parallel safety of the pathkeys too, otherwise we might
try sorting e.g. on results of a correlated subquery (as demonstrated
by a report from Luis Roberto).

Initial investigation by Tom Lane, patch by James Coleman. Backpatch
to 13, where the code was instroduced (as part of Incremental Sort).

Reported-by: Luis Roberto
Author: James Coleman
Reviewed-by: Tomas Vondra
Backpatch-through: 13
Discussion: https://postgr.es/m/622580997.37108180.1604080457319.JavaMail.zimbra%40siscobra.com.br
Discussion: https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs=hC0mSksZC=H5M8LSchj5e5OxpTAg@mail.gmail.com
This commit is contained in:
Tomas Vondra
2020-12-21 18:29:46 +01:00
parent f4a3c0b062
commit 86b7cca72d
5 changed files with 73 additions and 5 deletions
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5
src/include/optimizer/paths.h
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@@ -135,7 +135,10 @@ extern EquivalenceClass *get_eclass_for_sort_expr(PlannerInfo *root,
Relids rel,
bool create_it);
extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
extern Expr *find_em_expr_usable_for_sorting_rel(EquivalenceClass *ec, RelOptInfo *rel);
extern Expr *find_em_expr_usable_for_sorting_rel(PlannerInfo *root,
EquivalenceClass *ec,
RelOptInfo *rel,
bool require_parallel_safe);
extern void generate_base_implied_equalities(PlannerInfo *root);
extern List *generate_join_implied_equalities(PlannerInfo *root,
Relids join_relids,