Re: pg_stat_replication when standby is unreachable

On Wed, May 29, 2013 at 9:14 AM, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>wrote:

> Abhishek Rai <abhishekrai(at)gmail(dot)com> writes:
> > SELECT * from pg_stat_replication();
> >
> > I've noticed that when I terminate the standby (cleanly or through kill
> > -9), the result of above function goes from 1 row to zero rows. The
> result
> > comes back to 1 row when the standby restarts and reconnects. I was
> > wondering if there is any kind of guarantee about the results of
> > pg_stat_replication as the standby suffers a network partition, and/or
> > restarts and reconnects with the primary. Are there any parameters that
> > control this behavior?
>
> Not that I know of. We don't register standbies at all, so the master
> only knows about those which are successfully connected now.
>

Actually that is precisely what I need. If the master reports via
pg_stat_replication the set of standbies that it is connected to, then the
clustering software can just rely on it to know if standby is active or
not. However, this information is not very useful until there are some
guarantees on how long it would take for the response of
pg_stat_replication to be updated in response to an event. Without that,
the clustering software would not know how long to wait before declaring
the standby unhealthy. It's not a requirement that the timeout be
configurable, as long as it's deterministic.

Thanks for your help!
Abhishek

> Regards,
> --
> Dimitri Fontaine
> http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support
>