Re: Negative replication lag?

Ah, that makes sense. I think I'll add some logic to the script that has it
get new data points if it comes up with a negative value.

Thanks for the insight.

QH

On Mon, Apr 22, 2013 at 5:11 PM, Andres Freund <andres(at)2ndquadrant(dot)com>wrote:

> On 2013-04-22 16:36:38 -0600, Quentin Hartman wrote:
> > I'm using this script to check my replication lag on my streaming
> > replication pairs with Nagios:
> >
> > https://gist.github.com/jacobian/743942
> >
> > It generally works fine, but will occasionally return a negative lag
> value
> > (-37kb for example) which of course causes it to throw an alarm, but is
> > total nonsense. I've been working on the assumption that it is some sort
> of
> > bug in the script, but in taking a quick look at it nothing jumps out at
> me.
> >
> > Is there something in Postgres itself that could cause this to happen
> once
> > in awhile? Is it something to be concerned about? Is there a better way
> to
> > monitor this state?
>
> Well, between the time pg_current_xlog_location() is run on the primary
> and pg_last_xlog_replay_location() on the standby some time passes, so
> its not all that unlikely that wal has been generated, streamed *and*
> applied in that time. Given the short timeframe it only happens every
> now and then.
>
> Did you check the pg_stat_replication view on the primary?
>
> Greetings,
>
> Andres Freund
>
> --
> Andres Freund http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>