RE: Big performance slowdown from 11.2 to 13.3

-----Original Message-----
From: Peter Geoghegan <pg(at)bowt(dot)ie>
Sent: Thursday, July 22, 2021 12:14
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Jeff Davis <pgsql(at)j-davis(dot)com>; ldh(at)laurent-hasson(dot)com; David Rowley <dgrowleyml(at)gmail(dot)com>; Justin Pryzby <pryzby(at)telsasoft(dot)com>; pgsql-performance(at)postgresql(dot)org
Subject: Re: Big performance slowdown from 11.2 to 13.3

On Thu, Jul 22, 2021 at 8:45 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> That is ... weird. Maybe you have found a bug in the spill-to-disk
> logic; it's quite new after all. Can you extract a self-contained
> test case that behaves this way?

I wonder if this has something to do with the way that the input data is clustered. I recall noticing that that could significantly alter the behavior of HashAggs as of Postgres 13.

--
Peter Geoghegan

I could execute that test and re-cluster against the index. But I believe that's already done? Let me check.

Thank you,
Laurent.