| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, "ldh(at)laurent-hasson(dot)com" <ldh(at)laurent-hasson(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Big performance slowdown from 11.2 to 13.3 |
| Date: | 2021-07-22 16:53:21 |
| Message-ID: | CAH2-WzkWU_YdyKWSV2HeNyJk=ou6ywPH4S7Gd3XoJqZFbxF_ZA@mail.gmail.com |
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| Lists: | pgsql-performance |
On Thu, Jul 22, 2021 at 9:42 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Right. The point here is that before v13, hash aggregation was not
> subject to the work_mem limit, nor any related limit. If you did an
> aggregation requiring more than 2GB-plus-slop, it would work just fine
> as long as your machine had enough RAM. Now, the performance sucks and
> there is no knob you can turn to fix it. That's unacceptable in my book.
Oh! That makes way more sense.
I suspect David's theory about hash_agg_set_limits()'s ngroup limit is
correct. It certainly seems like a good starting point.
--
Peter Geoghegan
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