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Consider unsorted paths in generate_useful_gather_paths

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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
This commit is contained in:
Tomas Vondra
2020-12-21 18:09:57 +01:00
parent 29f8f54676
commit f4a3c0b062
3 changed files with 19 additions and 9 deletions
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11
src/backend/optimizer/path/allpaths.c
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@ -2900,7 +2900,8 @@ 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)
{
@ -2914,14 +2915,6 @@ 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 implicit sorting with a gather
* merge.
*/
if (subpath->pathkeys == NIL)
continue;
is_sorted = pathkeys_count_contained_in(useful_pathkeys,
subpath->pathkeys,
&presorted_keys);