Re: Enabling Checksums

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Daniel Farina <daniel(at)heroku(dot)com>, Greg Smith <greg(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)2ndquadrant(dot)com>, Ants Aasma <ants(at)cybertec(dot)at>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Enabling Checksums
Date: 2013-03-18 19:25:55
Message-ID: CA+U5nMK5ous2F4W6ZFsqeoCe_tw14nJpwt5J-b0=Sc0ScgEiqg@mail.gmail.com
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On 18 March 2013 19:02, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Sun, 2013-03-17 at 22:26 -0700, Daniel Farina wrote:
>> as long as I am able to turn them off easily
>
> To be clear: you don't get the performance back by doing
> "ignore_checksum_failure = on". You only get around the error itself,
> which allows you to dump/reload the good data.

Given that the worst pain point comes from setting hint bits during a
large SELECT, it makes sense to offer an option to simply skip hint
bit setting when we are reading data (SELECT, not
INSERT/UPDATE/DELETE). That seems like a useful option even without
checksums. I know I have seen cases across many releases where setting
that would have been good, since it puts the cleanup back onto
VACUUM/writers, rather than occasional SELECTs.

--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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