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Don't search for volatile expr in find_em_expr_usable_for_sorting_rel 

While prepare_sort_from_pathkeys has to be concerned about matching up
a volatile expression to the proper tlist entry, we don't need to do
that in find_em_expr_usable_for_sorting_rel becausee such a sort will
have to be postponed anyway.

Author: James Coleman
Reviewed-by: Tomas Vondra
Backpatch-through: 13
Discussion: https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs%3DhC0mSksZC%3DH5M8LSchj5e5OxpTAg%40mail.gmail.com
This commit is contained in:
Tomas Vondra 2020-12-21 19:37:14 +01:00
parent fac1b470a9
commit 9aff4dc01f
1 changed files with 5 additions and 23 deletions
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28
src/backend/optimizer/path/equivclass.c
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@ -816,8 +816,6 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
{
EquivalenceMember *em = lfirst(lc_em);
Expr *em_expr = em->em_expr;
PathTarget *target = rel->reltarget;
ListCell *lc_target_expr;
/*
* We shouldn't be trying to sort by an equivalence class that
@ -851,30 +849,14 @@ find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec,
* As long as the expression isn't volatile then
* prepare_sort_from_pathkeys is able to generate a new target entry,
* so there's no need to verify that one already exists.
*
* While prepare_sort_from_pathkeys has to be concerned about matching
* up a volatile expression to the proper tlist entry, it doesn't seem
* valuable here to expend the work trying to find a match in the
* target's exprs since such a sort will have to be postponed anyway.
*/
if (!ec->ec_has_volatile)
return em->em_expr;
/*
* If, however, it's volatile, we have to verify that the
* equivalence member's expr is already generated in the
* relation's target (we do strip relabels first from both
* expressions, which is cheap and might allow us to match
* more expressions).
*/
while (em_expr && IsA(em_expr, RelabelType))
em_expr = ((RelabelType *) em_expr)->arg;
foreach(lc_target_expr, target->exprs)
{
Expr *target_expr = lfirst(lc_target_expr);
while (target_expr && IsA(target_expr, RelabelType))
target_expr = ((RelabelType *) target_expr)->arg;
if (equal(target_expr, em_expr))
return em->em_expr;
}
}
/* We didn't find any suitable equivalence class expression */