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Order active window clauses for greater reuse of Sort nodes.

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By sorting the active window list lexicographically by the sort clause
list but putting longer clauses before shorter prefixes, we generate
more chances to elide Sort nodes when building the path.

Author: Daniel Gustafsson (with some editorialization by me)
Reviewed-by: Alexander Kuzmenkov, Masahiko Sawada, Tom Lane
Discussion: https://postgr.es/m/124A7F69-84CD-435B-BA0E-2695BE21E5C2%40yesql.se
This commit is contained in:
Andrew Gierth
2018-09-14 17:35:42 +01:00
parent 75f9c4ca5a
commit 728202b63c
4 changed files with 175 additions and 58 deletions
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7
src/backend/nodes/list.c
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@@ -1011,8 +1011,11 @@ list_append_unique_oid(List *list, Oid datum)
* via equal().
*
* This is almost the same functionality as list_union(), but list1 is
* modified in-place rather than being copied. Note also that list2's cells
* are not inserted in list1, so the analogy to list_concat() isn't perfect.
* modified in-place rather than being copied. However, callers of this
* function may have strict ordering expectations -- i.e. that the relative
* order of those list2 elements that are not duplicates is preserved. Note
* also that list2's cells are not inserted in list1, so the analogy to
* list_concat() isn't perfect.
*/
List *
list_concat_unique(List *list1, List *list2)