Re: Enabling Checksums

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Ants Aasma <ants(at)cybertec(dot)at>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Enabling Checksums
Date: 2013-03-27 14:15:19
Message-ID: 20130327141519.GC7148@alap2.anarazel.de
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On 2013-03-27 10:06:19 -0400, Robert Haas wrote:
> On Mon, Mar 18, 2013 at 4:31 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> > to get them going again. If the install had checksums, I could have figured
> > out which blocks were damaged and manually fixed them, basically go on a
> > hunt for torn pages and the last known good copy via full-page write.
>
> Wow. How would you extract such a block image from WAL?
>
> That would be a great tool to have, but I didn't know there was any
> practical way of doing it today.

Given pg_xlogdump that should be doable with 5min of hacking in 9.3. Just add
some hunk to write out the page to the if (config->bkp_details) hunk in
pg_xlogdump.c:XLogDumpDisplayRecord. I have done that for some debugging already.

If somebody comes up with a sensible & simple UI for this I am willing to
propose a patch adding it to pg_xlogdump. One would have to specify the
rel/file/node, the offset, and the target file.

Greetings,

Andres Freund

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

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