Negative replication lag?

[Quentin Hartman <qhartman@xxxxxxxxxxxxxxxxxxx>]

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?

Thanks!

QH