Greg Smith <gsmith(at)gregsmith(dot)com> wrote:
> Putting on my DBA hat for a minute, the first question I see people
> asking is "how do I measure how far behind the slaves are?".
> Presumably you can get that out of pg_controldata; my first question
> is whether that's complete enough information? If not, what else
> should be monitored?
>
> I don't think running that program going to fly for a production
> quality integrated replication setup though. The UI admins are
> going to want would allow querying this easily via a standard
> database query. Most monitoring systems can issue psql queries but
> not necessarily run a remote binary. I think that parts of
> pg_controldata needs to get exposed via some number of built-in UDFs
> instead, and whatever new internal state makes sense too. I could
> help out writing those, if someone more familiar with the
> replication internals can help me nail down a spec on what to watch.
IMO, it would be best if the status could be sent via NOTIFY. In my
experience, this results in monitoring which both has less overhead
and is more current. We tend to be almost as interested in metrics on
throughput as lag. Backlogged volume can be interesting, too, if it's
available.
-Kevin