Re: Hot Standby (v9d)

On Wed, 2009-01-28 at 22:47 +0200, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > The essential choice is "What would you like the max failover time to
> > be?". Some users want one server with max 5 mins behind, some want two
> > servers, one with 0 seconds behind, one with 12 hours behind
>
> It's not quite that simple.

In this case, yes it is.

> Setting max_standby_delay=5mins means that
> you're willing to wait 5 minutes for each query to die. Which means that
> in worst case you have to stop for 5 minutes at every single vacuum
> record, and fall behind much more than 5 minutes.

That's not how this patch works.

> You could make it more like that by tracking the timestamps in commit
> records

Which is what we do.

> It should also be noted that the control functions allow you to connect
> to the database and manually pause/resume the replay. So you can for
> example set max_standby_delay=0 during the day, but pause the replay
> manually before starting a nightly report.

Yes, thank you for bringing balance to the discussions.

Please everybody read this before commenting further.

http://wiki.postgresql.org/wiki/Hot_Standby#Usage

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support