Re: Enabling Checksums

On Wed, Mar 27, 2013 at 10:15 AM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> 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.

Hmm. Cool. But, wouldn't the hard part be to figure out where to
start reading the WAL in search of the *latest* FPI?

--
Robert Haas
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