Re: Avoid computing ORDER BY junk columns unnecessarily
| От | Richard Guo |
|---|---|
| Тема | Re: Avoid computing ORDER BY junk columns unnecessarily |
| Дата | |
| Msg-id | CAMbWs48z9NqdwL6LnQZwnV8RR=BKEpXyDLoYaj5RzFOMvFheaw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Avoid computing ORDER BY junk columns unnecessarily (Tom Lane <tgl@sss.pgh.pa.us>) |
| Список | pgsql-hackers |
On Sat, Dec 23, 2023 at 1:32 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Heikki Linnakangas <hlinnaka@iki.fi> writes:
> On 22/12/2023 17:24, Tom Lane wrote:
>> How much of your patchset still makes sense if we assume that we
>> can always extract the ORDER BY column values from the index?
> That would make it much less interesting. But I don't think that's a
> good assumption. Especially in the kNN case, the ORDER BY value would
> not be stored in the index. Most likely the index needs to calculate it
> in some form, but it might take shortcuts like avoiding the sqrt().
Yeah, fair point. I'll try to take a look at your patchset after
the holidays.
Agreed.
I haven't looked into these patches, but it seems that there is an issue
with how the targetlist is handled for foreign rels. The following test
case for postgres_fdw hits the Assert in apply_tlist_labeling().
contrib_regression=# SELECT c3, c4 FROM ft1 ORDER BY c3, c1 LIMIT 1;
server closed the connection unexpectedly
When we create foreign final path in add_foreign_final_paths(), we use
root->upper_targets[UPPERREL_FINAL] as the PathTarget. This PathTarget
is set in grouping_planner(), without removing the junk columns. I
think this is why the above query hits the Assert.
Thanks
Richard
I haven't looked into these patches, but it seems that there is an issue
with how the targetlist is handled for foreign rels. The following test
case for postgres_fdw hits the Assert in apply_tlist_labeling().
contrib_regression=# SELECT c3, c4 FROM ft1 ORDER BY c3, c1 LIMIT 1;
server closed the connection unexpectedly
When we create foreign final path in add_foreign_final_paths(), we use
root->upper_targets[UPPERREL_FINAL] as the PathTarget. This PathTarget
is set in grouping_planner(), without removing the junk columns. I
think this is why the above query hits the Assert.
Thanks
Richard
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