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Improve find_em_expr_usable_for_sorting_rel comment

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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
This commit is contained in:
Tomas Vondra
2020-12-22 02:00:39 +01:00
parent 9aff4dc01f
commit 1ca2eb1031
2 changed files with 8 additions and 3 deletions
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3
src/backend/optimizer/plan/createplan.c
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@ -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,