Re: Moving data from huge table slow, min() query on indexed column taking 38s

From: Dimitrios Apostolou <jimis(at)gmx(dot)net>
To: pgsql-general(at)lists(dot)postgresql(dot)org
Subject: Re: Moving data from huge table slow, min() query on indexed column taking 38s
Date: 2023-07-06 16:11:53
Message-ID: a73dd30b-3dee-6e02-9eff-a90a8dd02e8f@gmx.net
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On Thu, 6 Jul 2023, Dimitrios Apostolou wrote:

> + First I chose the method to DELETE...INSERT everything.

Just to clarify, the query looked more like

WITH rows AS ( DELETE FROM tbl_legacy RETURNING * )
INSERT INTO tbl
SELECT * FROM rows;

> I noticed that the postgres process was growing without bounds, up to
> the point that it consumed almost all of swap space and I had to kill
> the command. Any idea why that happens?

Also note that my settings for work_mem, temp_buffers, shared_buffers etc
are all well below the RAM size and postgres has never shown unbound
growth again. Postgres version is 15.2.

Dimitris

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