Date: Tue, 5 May 2020 14:28:36 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Jamie Thompson <jthompson.neuk@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Please help! Query jumps from 1s -> 4m
Message-ID: <20200505192836.GD28974@telsasoft.com>
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On Mon, May 04, 2020 at 02:12:01PM -0500, Justin Pryzby wrote:
> On Mon, May 04, 2020 at 08:07:07PM +0100, Jamie Thompson wrote:
> > Additionally, the execution plans for the 10th + following queries look
> > fine, they have the same structure as if I run the query manually. It's not
> > that the query plan switches, it seems as though the same query plan is
> > just > 200X slower than usual.
> 
> Are you able to reproduce the problem manually ?
> 
> With/without PREPARE ?
> https://www.postgresql.org/docs/current/sql-prepare.html

Also, you should be able to check if that's the problem by doing either:
plan_cache_mode = force_generic_plan;
Or (I would think) DISCARD PLANS;

https://www.postgresql.org/docs/12/runtime-config-query.html

-- 
Justin