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| author | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-12-22 02:00:39 +0100 |
|---|---|---|
| committer | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-12-22 02:00:51 +0100 |
| commit | 1ca2eb103113d64930cf1120ba2beaaebd1076f4 (patch) | |
| tree | 509b74587f193d371b22e9422f161798f58f3401 | |
| parent | 9aff4dc01fbb9e126efafd839ae8541362328f1a (diff) | |
| download | postgresql-1ca2eb103113d64930cf1120ba2beaaebd1076f4.tar.gz postgresql-1ca2eb103113d64930cf1120ba2beaaebd1076f4.zip | |
Improve find_em_expr_usable_for_sorting_rel comment
Clarify the relationship between find_em_expr_usable_for_sorting_rel and
prepare_sort_from_pathkeys, i.e. what restrictions need to be shared
between those two places.
Author: James Coleman
Reviewed-by: Tomas Vondra
Backpatch-through: 13
Discussion: https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs%3DhC0mSksZC%3DH5M8LSchj5e5OxpTAg%40mail.gmail.com
| -rw-r--r-- | src/backend/optimizer/path/equivclass.c | 8 | ||||
| -rw-r--r-- | src/backend/optimizer/plan/createplan.c | 3 |
2 files changed, 8 insertions, 3 deletions
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index 600fa1263a7..c33af06ec0e 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -798,9 +798,11 @@ find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel) } /* - * Find an equivalence class member expression that can be safely used by a - * sort node on top of the provided relation. The rules here must match those - * applied in prepare_sort_from_pathkeys. + * Find an equivalence class member expression that can be safely used to build + * a sort node using the provided relation. The rules are a subset of those + * applied in prepare_sort_from_pathkeys since that function deals with sorts + * that must be delayed until the last stages of query execution, while here + * we only care about proactive sorts. */ Expr * find_em_expr_usable_for_sorting_rel(PlannerInfo *root, EquivalenceClass *ec, diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c index 5ecf9f40658..f7a8dae3c64 100644 --- a/src/backend/optimizer/plan/createplan.c +++ b/src/backend/optimizer/plan/createplan.c @@ -5850,6 +5850,9 @@ make_incrementalsort(Plan *lefttree, int numCols, int nPresortedCols, * * Returns the node which is to be the input to the Sort (either lefttree, * or a Result stacked atop lefttree). + * + * Note: Restrictions on what expressions are safely sortable may also need to + * be added to find_em_expr_usable_for_sorting_rel. */ static Plan * prepare_sort_from_pathkeys(Plan *lefttree, List *pathkeys, |