Re: recovery_target_action = pause & hot_standby = off

On Sun, Mar 15, 2015 at 3:16 PM, Andres Freund <andres(at)2ndquadrant(dot)com>
wrote:

> On 2015-03-15 14:51:46 +0100, Magnus Hagander wrote:
> > On Sun, Mar 15, 2015 at 2:27 PM, Andres Freund <andres(at)2ndquadrant(dot)com>
> > wrote:
> >
> > > On 2015-03-12 15:52:02 +0100, Andres Freund wrote:
> > > > /*
> > > > * Override any inconsistent requests. Not that this is a
> change
> > > > * of behaviour in 9.5; prior to this we simply ignored a
> request
> > > > * to pause if hot_standby = off, which was surprising
> behaviour.
> > > > */
> > > > if (recoveryTargetAction == RECOVERY_TARGET_ACTION_PAUSE &&
> > > > recoveryTargetActionSet &&
> > > > standbyState == STANDBY_DISABLED)
> > > > recoveryTargetAction = RECOVERY_TARGET_ACTION_SHUTDOWN;
> > >
> > > While it's easy enough to fix I rather dislike the whole intent here
> > > though. *Silently* switching the mode of operation in a rather
> > > significant way seems like a bad idea to me. At the very least we need
> > > to emit a LOG message about this; but I think it'd be much better to
> > > error out instead.
> > >
> > > <9.5's behaviour was already quite surprising. But changing things to a
> > > different surprising behaviour seems like a bad idea.
> > >
> >
> > +1. Especially for "sensitive" operations like this, having
> > predictable-behavior-or-error is usually the best choice.
>
> Yea.
>
> Looking further, it's even worse right now. We'll change the target to
> shutdown when hot_standby = off, but iff it was set in the config
> file. But the default value is (and was, although configured
> differently) documented to be 'pause'; so if it's not configured
> explicitly we still will promote. At least I can't read that out of the
> docs.
>
> Personally I think we just should change the default to 'shutdown' for
> all cases. That makes documentation and behaviour less surprising. And
> makes experimenting less dangerous, since you can just start again.
>

+1. These things need to be clear. Given the consequences of getting it
wrong, surprising behavior can be quite dangerous.

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/