Re: Online enabling of checksums

From: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
To: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Cc: Daniel Gustafsson <daniel(at)yesql(dot)se>, Michael Banck <michael(dot)banck(at)credativ(dot)de>, Magnus Hagander <magnus(at)hagander(dot)net>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Online enabling of checksums
Date: 2018-03-20 09:29:41
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> 19 марта 2018 г., в 11:27, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> написал(а):
> Is there no way to stop the checksum helper once it's started? That seems rather user-unfriendly. I can imagine it being a pretty common mistake to call pg_enable_data_checksums() on a 10 TB cluster, only to realize that you forgot to set the cost limit, and that it's hurting queries too much. At that point, you want to abort.
I've tried to pg_cancel_backend() and it worked.
But only if I cancel "checksum helper launcher" and then "checksum helper worker". If I cancel helper first - it spawns new.

Magnus, Daniel, is it safe to cancel worker or launcher?

BTW, I have some questions on pg_verify_chechsums.
It does not check catalog version. It it true that it will work for any?
Also, pg_verify_chechsums will stop on short reads. But we do not stop on wrong checksum, may be we should not stop on short reads either?

I agree with all of Heikki's comments.

Besides these I have no other questions, patch looks good.

Best regards, Andrey Borodin.

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