Re: Hot standby and b-tree killed items

On Saturday 20 December 2008 04:10:21 Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > On Sat, 2008-12-20 at 09:21 +0200, Heikki Linnakangas wrote:
> >> Gregory Stark wrote:
> >>> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> >>>> Increasing the waiting time increases the failover time and thus
> >>>> decreases the value of the standby as an HA system. Others value high
> >>>> availability higher than you and so we had agreed to provide an option
> >>>> to allow the max waiting time to be set.
> >>>
> >>> Sure, it's a nice option to have. But I think the default should be to
> >>> pause WAL replay.
> >>
> >> I think I agree that pausing should be the default. If for no other
> >> reason, because I can't think of a good default for max_standby_delay.
> >
> > I would rather err on the side of caution. If we do as you suggest,
> > somebody will lose their database and start shouting "stupid default".
>
> Even if we stop applying the WAL, it should still be archived safely,
> right? So no data should be lost, although the standby can fall very
> much behind, and it can take a while to catch up.
>

I was thinking the condition Simon was concerned about was that on a very busy
slave with wal delay, you could theoretically fill up the disks and destroy
the slave. With query cancel, you might be annoyed to see the queries
canceled, but theres no way that you would destroy the slave. (That might not
have been what he meant though)

--
Robert Treat
Conjecture: http://www.xzilla.net
Consulting: http://www.omniti.com