Horton

Re: Time to increase hash_mem_multiplier default?

John Naylor <john.naylor@enterprisedb.com>

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From: John Naylor <john.naylor@enterprisedb.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-01-19T19:31:51Z
Lists: pgsql-hackers 
On Sun, Jan 16, 2022 at 7:28 PM Peter Geoghegan <pg@bowt.ie> wrote:
>
> The current hash_mem_multiplier default is 1.0, which is a fairly
> conservative default: it preserves the historic behavior, which is
> that hash-based executor nodes receive the same work_mem budget as
> sort-based nodes. I propose that the default be increased to 2.0 for
> Postgres 15.

I don't have anything really profound to say here, but in the last
year I did on a couple occasions recommend clients to raise
hash_mem_multiplier to 2.0 to fix performance problems.

During this cycle, we also got a small speedup in the external sorting
code. Also, if the "generation context" idea gets traction, that might
be another reason to consider differentiating the mem settings.
--
John Naylor
EDB: http://www.enterprisedb.com

Commits

  1. Increase hash_mem_multiplier default to 2.0.