RE: Big performance slowdown from 11.2 to 13.3

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

On Thu, Jul 22, 2021 at 8:45 AM Tom Lane <tgl@sss.pgh.pa.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.