Re: recovery_target_action = pause & hot_standby = off

On 2015-03-15 20:10:49 +0000, Simon Riggs wrote:
> On 15 March 2015 at 14:16, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>
> > 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.
>
> We need to look at the specific situation, not make a generic decision.
>
> If hot_standby = off, we are unable to unpause, once paused.
>
> Changing the default doesn't alter that problem.
>
> We have two choices: 1) override to a sensible setting, 2) throw an error.
>
> (2) sounds clean at first but we must look deeper. We know that the
> *only* possible other setting is 'shutdown', so it seems more user
> friendly to do the thing we *know* they want (1), rather than pretend
> that we don't.
>
> (1) is completely predictable and not at all surprising. Add a LOG
> message if you wish, but don't throw an error.

Sorry, I don't buy this. If I have "recovery_target_action = 'pause'" in
the config file, I want it to pause. Not do something else, just because
postgres doesn't have a interface to unpause without SQL access. That
makes some sense to developers, but is pretty much ununderstandable for
mere mortals.

Even worse, right now (after the bugfix), the behaviour is:

postgresql.conf:
# hot_standby = off
recovery.conf:
#recovery_target_action = 'pause'
=> promote (the downgrading is only active when explicitly configured)

# hot_standby = off
recovery.conf:
recovery_target_action = 'pause'
=> shutdown (despite an explicit setting of pause)

hot_standby = on
recovery.conf:
# recovery_target_action = 'pause'
=> pause

hot_standby = on
recovery.conf:
recovery_target_action = 'pause'
=> pause

To me that's just utterly confusing.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services