Re: locate DB corruption

On 08/31/2018 08:51 AM, Dave Peticolas wrote:
> On Fri, Aug 31, 2018 at 8:14 AM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com
> <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
>
> On 08/31/2018 08:02 AM, Dave Peticolas wrote:
> > Hello, I'm running into the following error running a large query
> on a
> > database restored from WAL replay:
> >
> > could not access status of transaction 330569126
> > DETAIL: Could not open file "pg_clog/0C68": No such file or directory
>
>
> Postgres version?
>
>
> Right! Sorry, that original email didn't have a lot of info. This is
> 9.6.9 restoring a backup from 9.6.8.
>
> Where is the replay coming from?
>
>
> From a snapshot and WAL files stored in Amazon S3.

Seems the process is not creating a consistent backup.

How are they being generated?

> Are you sure you are not working across versions?
>
>
> I am sure, they are all 9.6.
>
> If not do pg_clog/ and 0C68 actually exist?
>
>
> pg_clog definitely exists, but 0C68 does not. I think I have
> subsequently found the precise row in the specific table that seems to
> be the problem. Specifically I can select * from TABLE where id = BADID
> - 1 or id = BADID + 1 and the query returns. I get the error if I select
> the row with the bad ID.
>
> Now what I'm not sure of is how to fix.

One thing I can think of is to rebuild from a later version of your S3
data and see if it has all the necessary files.

There is also pg_resetxlog:

https://www.postgresql.org/docs/9.6/static/app-pgresetxlog.html

I have not used it, so I can not offer much in the way of tips. Just
from reading the docs I would suggest stopping the server and then
creating a backup of $PG_DATA(if possible) before using pg_resetxlog.

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com