I am not sure I understand this parameter well enough but it’s with a default value right now of 1000. I have read Robert’s post (http://rhaas.blogspot.com/2018/06/using-forceparallelmode-correctly.html) and could play with those parameters, but unsure whether what you are describing will unlock this 2GB limit.
From: Vijaykumar Jain <vijaykumarjain.github@gmail.com> Sent: Thursday, July 22, 2021 16:32 To: ldh@laurent-hasson.com Cc: Justin Pryzby <pryzby@telsasoft.com>; pgsql-performance@postgresql.org Subject: Re: Big performance slowdown from 11.2 to 13.3
Just asking, I may be completely wrong.
is this query parallel safe?
can we force parallel workers, by setting low parallel_setup_cost or otherwise to make use of scatter gather and Partial HashAggregate(s)?
I am just assuming more workers doing things in parallel, would require less disk spill per hash aggregate (or partial hash aggregate ?) and the scatter gather at the end.
I did some runs in my demo environment, not with the same query, some group by aggregates with around 25M rows, and it showed reasonable results, not too off.
