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.comPostgreSQL Training, Services and Support