Re: Big performance slowdown from 11.2 to 13.3 - Mailing list pgsql-performance

From Tom Lane
Subject Re: Big performance slowdown from 11.2 to 13.3
Date
Msg-id 786600.1626970898@sss.pgh.pa.us
Whole thread Raw
In response to Re: Big performance slowdown from 11.2 to 13.3  (David Rowley <dgrowleyml@gmail.com>)
Responses Re: Big performance slowdown from 11.2 to 13.3  (Tom Lane <tgl@sss.pgh.pa.us>)
Re: Big performance slowdown from 11.2 to 13.3  (Peter Geoghegan <pg@bowt.ie>)
List pgsql-performance
David Rowley <dgrowleyml@gmail.com> writes:
> On Fri, 23 Jul 2021 at 03:56, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> So basically, we now have a hard restriction that hashaggs can't use
>> more than INT_MAX kilobytes, or approximately 2.5GB, and this use case
>> is getting eaten alive by that restriction.  Seems like we need to
>> do something about that.

> Hmm, math check?

Yeah, I should have said "2GB plus palloc slop".  It doesn't surprise
me a bit that we seem to be eating another 20% on top of the nominal
limit.

I think the right fix here is to remove the cap, which will require
changing get_hash_mem to return double, and then maybe some cascading
changes --- I've not looked at its callers.

            regards, tom lane



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