Horton

Re: Big performance slowdown from 11.2 to 13.3

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: "ldh@laurent-hasson.com" <ldh@laurent-hasson.com>
Cc: Peter Geoghegan <pg@bowt.ie>, David Rowley <dgrowleyml@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: 2021-07-28T03:15:52Z
Lists: pgsql-performance 
"ldh@laurent-hasson.com" <ldh@laurent-hasson.com> writes:
> One question that popped up in my head. hash_mem_multiplier is an upper-bound right: it doesn't reserve memory ahead of time correct? So there is no reason for me to spend undue amounts of time fine-tuning this parameter? If I have work_mem to 521MB, then I can set hash_mem_multiplier to 8 and should be OK. This doesn't mean that every query will consume 4GB of memory.

Yeah, I wouldn't sweat over the specific value.  The pre-v13 behavior
was effectively equivalent to hash_mem_multiplier = infinity, so if
you weren't having any OOM problems before, just crank it up.

			regards, tom lane

Commits

  1. Get rid of artificial restriction on hash table sizes on Windows.