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| author | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-12-21 18:16:16 +0100 |
|---|---|---|
| committer | Tomas Vondra <tomas.vondra@postgresql.org> | 2020-12-21 18:16:36 +0100 |
| commit | ea190ed14b4b75b38a490707d5d08231dcacfb8c (patch) | |
| tree | b477d11e0e979ae28a991483344fad2dce8eacae | |
| parent | bd6939a4e22ff5cc4ed77eec2c3c2d4c58ea2143 (diff) | |
| download | postgresql-ea190ed14b4b75b38a490707d5d08231dcacfb8c.tar.gz postgresql-ea190ed14b4b75b38a490707d5d08231dcacfb8c.zip | |
Consider unsorted paths in generate_useful_gather_paths
generate_useful_gather_paths used to skip unsorted paths (without any
pathkeys), but that is unnecessary - the later code actually can handle
such paths just fine by adding a Sort node. This is clearly a thinko,
preventing construction of useful plans.
Backpatch to 13, where Incremental Sort was introduced.
Author: James Coleman
Reviewed-by: Tomas Vondra
Backpatch-through: 13
Discussion: https://postgr.es/m/CAAaqYe8cK3g5CfLC4w7bs=hC0mSksZC=H5M8LSchj5e5OxpTAg@mail.gmail.com
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 11 | ||||
| -rw-r--r-- | src/test/regress/expected/incremental_sort.out | 13 | ||||
| -rw-r--r-- | src/test/regress/sql/incremental_sort.sql | 4 |
3 files changed, 19 insertions, 9 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index 09a0ee24d60..fa2cf61329c 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -2840,7 +2840,8 @@ generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_r cheapest_partial_path = linitial(rel->partial_pathlist); /* - * Consider incremental sort paths for each interesting ordering. + * Consider sorted paths for each interesting ordering. We generate both + * incremental and full sort. */ foreach(lc, useful_pathkeys_list) { @@ -2854,14 +2855,6 @@ generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_r Path *subpath = (Path *) lfirst(lc2); GatherMergePath *path; - /* - * If the path has no ordering at all, then we can't use either - * incremental sort or rely on implict sorting with a gather - * merge. - */ - if (subpath->pathkeys == NIL) - continue; - is_sorted = pathkeys_count_contained_in(useful_pathkeys, subpath->pathkeys, &presorted_keys); diff --git a/src/test/regress/expected/incremental_sort.out b/src/test/regress/expected/incremental_sort.out index 7cf2eee7c14..51471ae92de 100644 --- a/src/test/regress/expected/incremental_sort.out +++ b/src/test/regress/expected/incremental_sort.out @@ -1468,6 +1468,19 @@ explain (costs off) select * from t union select * from t order by 1,3; -> Parallel Seq Scan on t t_1 (13 rows) +-- Full sort, not just incremental sort can be pushed below a gather merge path +-- by generate_useful_gather_paths. +explain (costs off) select distinct a,b from t; + QUERY PLAN +------------------------------------------ + Unique + -> Gather Merge + Workers Planned: 2 + -> Sort + Sort Key: a, b + -> Parallel Seq Scan on t +(6 rows) + drop table t; -- Sort pushdown can't go below where expressions are part of the rel target. -- In particular this is interesting for volatile expressions which have to diff --git a/src/test/regress/sql/incremental_sort.sql b/src/test/regress/sql/incremental_sort.sql index 3ee11c394b9..cb48f200ce5 100644 --- a/src/test/regress/sql/incremental_sort.sql +++ b/src/test/regress/sql/incremental_sort.sql @@ -220,6 +220,10 @@ explain (costs off) select a,b,sum(c) from t group by 1,2 order by 1,2,3 limit 1 set enable_hashagg to off; explain (costs off) select * from t union select * from t order by 1,3; +-- Full sort, not just incremental sort can be pushed below a gather merge path +-- by generate_useful_gather_paths. +explain (costs off) select distinct a,b from t; + drop table t; -- Sort pushdown can't go below where expressions are part of the rel target. |