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Fix get_useful_pathkeys_for_relation for volatile expressions

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When considering Incremental Sort below a Gather Merge, we need to be
a bit more careful when matching pathkeys to EC members. It's not enough
to find a member whose Vars are all in the current relation's target;
volatile expressions in particular need to be contained in the target,
otherwise it's too early to use the pathkey.

Reported-by: Jaime Casanova
Author: James Coleman
Reviewed-by: Tomas Vondra
Backpatch-through: 13, where the incremental sort code was added
Discussion: https://postgr.es/m/CAJGNTeNaxpXgBVcRhJX%2B2vSbq%2BF2kJqGBcvompmpvXb7pq%2BoFA%40mail.gmail.com
This commit is contained in:
Tomas Vondra
2020-11-03 20:07:23 +01:00
parent 92f87182f2
commit ebb7ae839d
5 changed files with 207 additions and 6 deletions
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13
src/backend/optimizer/path/allpaths.c
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@@ -2816,7 +2816,8 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
/*
* Considering query_pathkeys is always worth it, because it might allow
* us to avoid a total sort when we have a partially presorted path
* available.
* available or to push the total sort into the parallel portion of the
* query.
*/
if (root->query_pathkeys)
{
@@ -2829,17 +2830,17 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
/*
* We can only build an Incremental Sort for pathkeys which
* contain an EC member in the current relation, so ignore any
* suffix of the list as soon as we find a pathkey without an EC
* member the relation.
* We can only build a sort for pathkeys which contain an EC
* member in the current relation's target, so ignore any suffix
* of the list as soon as we find a pathkey without an EC member
* in the relation.
*
* By still returning the prefix of the pathkeys list that does
* meet criteria of EC membership in the current relation, we
* enable not just an incremental sort on the entirety of
* query_pathkeys but also incremental sort below a JOIN.
*/
if (!find_em_expr_for_rel(pathkey_ec, rel))
if (!find_em_expr_usable_for_sorting_rel(pathkey_ec, rel))
break;
npathkeys++;