Date: Tue, 17 Nov 2020 10:06:22 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Frits Jalvingh <jal@etc.to>
Cc: pgsql-performance@postgresql.org
Subject: Re: Postgres using nested loops despite setting enable_nestloop to
 false
Message-ID: <20201117160622.GB24784@telsasoft.com>
References: 
 <CAKhTGFXJh6QfZTTXw4Qb-7oiFwgqh7Pdz0nUKjZnayuZpwjGqg@mail.gmail.com>
 <20201117142024.GA24784@telsasoft.com>
 <CAKhTGFUzjFaDon6cjF7NsWhDA0yXUHbhbAF66CZdaVK_v_YqVQ@mail.gmail.com>
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On Tue, Nov 17, 2020 at 04:58:45PM +0100, Frits Jalvingh wrote:
> Hi Justin, thanks for your help!
> I have attached both plans, both made with set enable_nestloop = false in
> the attachments.
> On the Postgresql 13 server work_mem is 64MB. It cannot really be higher
> there because Postgresql does not control its use of memory, setting it
> higher on this VM will cause the OOM killer to kill Postgresql for some
> queries.

Can you try to get an explain just for this query with either increased
work_mem or hash_mem_multiplier ?

Or possibly by messing with the cost parameters, including seq_page_cost.
Making all cost_* params 1000x smaller might allow the disable cost to be
effective.

-- 
Justin