Re: Enabling Checksums

On 2013-03-27 10:06:19 -0400, Robert Haas wrote:
> On Mon, Mar 18, 2013 at 4:31 PM, Greg Smith <greg@2ndquadrant.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