Re: Hot Backup with rsync fails at pg_clog if under load

On Fri, Sep 23, 2011 at 12:58 PM, Heikki Linnakangas
<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
> There are pretty clear rules on what state clog can be in. When you launch
> postmaster in a standby:
>
> * Any clog preceding the nextXid from the checkpoint record we start
> recovery from, must either be valid, or the clog file must be missing
> altogether (which can happen when it was vacuumed away while the backup in
> progress - if the clog is still needed at the end of backup it must not be
> missing, of course).
> * Any clog following nextXid can be garbled or missing.
>
> Recovery will overwrite any clog after nextXid from the WAL, but not the
> clog before it.

So the actual error message in the last test was:

2011-09-21 13:41:05 CEST FATAL: could not access status of transaction 1188673

...but we can't tell if that was before or after nextXid, which seems
like it would be useful to know.

If Linas can rerun his experiment, but also capture the output of
pg_controldata before firing up the standby for the first time, then
we'd able to see that information.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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