Re: Calculating Replication Lag - units

On Mon, Jun 25, 2012 at 02:17:22PM -0700, Steve Crawford wrote:
- On 06/25/2012 01:17 PM, David Kerr wrote:
- >Howdy,
- >
- >When calculating Replication lag, I know that we have to compare the
- >pg_current_xlog_location
- >to pg_last_xlog_receive_location, etc. but what I'm trying to figure out
- >is what are
- >the units that I'm left with after the calculation.
- >
- >(i.e., does the xlog_location imply some time value?)
- >
- >Here's the output of the (slightly modified script)
- >Master: 5003964876715
- >Receive: 5003964876715
- >Replay: 5003964765203
- >
- >receive.value 0
- >apply.value 111512
- >
- >111512 isn't inherently useful to me on its own.
- >
- >Any tips?
- >
- How about now()-pg_last_xact_replay_timestamp() (however this can be a
- large number if there have not been any recent transactions on the
- master). I suppose you could do something like:
-
- case when pg_last_xlog_receive_location() =
- pg_last_xlog_replay_location() then '0 seconds'::interval
- else now()-pg_last_xact_replay_timestamp() end as log_delay;

i don't know for sure that 111512 is a time value.. that's kind of
what i'm wondering. If i knew that it was like miliseconds or something
that would be helpful.

- But I'm wrapping my head around some replication issues myself so others
- may have better ideas or corrections.

I've been fairly successful with replication so I'm happy to help there.
Just trying to shore up my monitoring now!