Re: Performance degradation if query returns no rows and column expression is used after upgrading to 12

From: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
To: Andrus <kobruleht2(at)hot(dot)ee>
Cc: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Re: Performance degradation if query returns no rows and column expression is used after upgrading to 12
Date: 2020-04-07 17:26:22
Message-ID: CAFj8pRA9bk4_cYUj9=UWG-XyKfeRCawFD0j-BBRp0+4Z8u2Bjw@mail.gmail.com
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út 7. 4. 2020 v 19:09 odesílatel Andrus <kobruleht2(at)hot(dot)ee> napsal:

> Hi!
> >on your query there is too slow JIT. Is strange how much. So the best way
> is disable JIT probably
> >set jit to off;
> >or same field in postgresql.conf
>
> Thank you.
>
> set jit to off
>
> makes select fast.
> I have encountered this issue only in this query in one database
>
> There is variation of this query running with diferent data in different
> database in same Debian 10 server. It works fast.
> Should I disable jit only for this query or in postgresql.conf permanently?
>

you can do it in session

SET jit to off;
SELECT ..
SET jit to DEFAULT;

It is really strange why it is too slow. Can you prepare test case? Looks
like bug (maybe not Postgres's bug)

Pavel

> Andrus.
>

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