Re: Trouble with hashagg spill I/O pattern and costing
| От | Melanie Plageman |
|---|---|
| Тема | Re: Trouble with hashagg spill I/O pattern and costing |
| Дата | |
| Msg-id | CAAKRu_YNGQ-zw9rpXGtYhURMqdPk+HnMa+Wj-tnNx9cwENgDxg@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Trouble with hashagg spill I/O pattern and costing (Jeff Davis <pgsql@j-davis.com>) |
| Ответы |
Re: Trouble with hashagg spill I/O pattern and costing
|
| Список | pgsql-hackers |
On Tue, May 26, 2020 at 5:40 PM Jeff Davis <pgsql@j-davis.com> wrote:
On Tue, 2020-05-26 at 21:15 +0200, Tomas Vondra wrote:
>
> As for the tlist fix, I think that's mostly ready too - the one thing
> we
> should do is probably only doing it for AGG_HASHED. For AGG_SORTED
> it's
> not really necessary.
Melanie previously posted a patch to avoid spilling unneeded columns,
but it introduced more code:
https://www.postgresql.org/message-id/CAAKRu_aefEsv+UkQWqu+ioEnoiL2LJu9Diuh9BR8MbyXuZ0j4A@mail.gmail.com
and it seems that Heikki also looked at it. Perhaps we should get an
acknowledgement from one of them that your one-line change is the right
approach?
I spent some time looking at it today, and, it turns out I was wrong.
I thought that there was a case I had found where CP_SMALL_TLIST did not
eliminate as many columns as could be eliminated for the purposes of
spilling, but, that turned out not to be the case.
I changed CP_LABEL_TLIST to CP_SMALL_TLIST in
create_groupingsets_plan(), create_agg_plan(), etc and tried a bunch of
different queries and this 2-3 line change worked for all the cases I
tried. Is that where you made the change?
And then are you proposing to set it based on the aggstrategy to either
CP_LABEL_TLIST or CP_SMALL_TLIST here?
I thought that there was a case I had found where CP_SMALL_TLIST did not
eliminate as many columns as could be eliminated for the purposes of
spilling, but, that turned out not to be the case.
I changed CP_LABEL_TLIST to CP_SMALL_TLIST in
create_groupingsets_plan(), create_agg_plan(), etc and tried a bunch of
different queries and this 2-3 line change worked for all the cases I
tried. Is that where you made the change?
And then are you proposing to set it based on the aggstrategy to either
CP_LABEL_TLIST or CP_SMALL_TLIST here?
--
Melanie Plageman
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