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From: Justin Pryzby <pryzby@telsasoft.com>
To: Alex Kaiser <alextkaiser@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: ranier.vf@gmail.com
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: Getting an index scan to be a parallel index scan
Date: Wed, 1 Feb 2023 14:02:39 -0600
Message-ID: <20230201200239.GV22427@telsasoft.com> (raw)
In-Reply-To: <CAN4ko3CMqw352BpfVxPih8qH_yE4rymBb0OcjAEemSrCm+Ea9A@mail.gmail.com>
References: <CAN4ko3B4y75pg5Ro_oAjWf8L1HYSYgXcDgsS6nzOTvQOkKnM1Q@mail.gmail.com>
	<CAApHDvrsoY1aUroQ6SHD6orEGRxi7LQtV6ejoMt5-vQJ636xOw@mail.gmail.com>
	<CAN4ko3CMqw352BpfVxPih8qH_yE4rymBb0OcjAEemSrCm+Ea9A@mail.gmail.com>

On Wed, Feb 01, 2023 at 11:22:47AM -0800, Alex Kaiser wrote:
> I've never messed around with extended statistics, but I'm not sure how
> they would help here. From what I've read they seem to help when your query
> is restricting over multiple columns. Since this query is only on one
> column I'm not sure what a good "CREATE STATISTICS ..." command to run
> would be to improve the query plan. Any suggestions?

They wouldn't help.  It seems like that was a guess.

> As for how I found 'force_parallel_mode', I think I found it first here:
> https://postgrespro.com/list/thread-id/2574997 and then I also saw it when
> I was searching for 'parallel' on https://postgresqlco.nf .

Yeah.  force_parallel_mode is meant for debugging, only, and we're
wondering how people end up trying to use it for other purposes.

http://rhaas.blogspot.com/2018/06/using-forceparallelmode-correctly.html

Did you try adjusting min_parallel_index_scan_size /
min_parallel_table_scan_size ?

-- 
Justin





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