Re: Standby accepts recovery_target_timeline setting?

On 9/26/19 4:48 PM, Peter Eisentraut wrote:
> On 2019-09-25 22:21, David Steele wrote:
>> While testing against PG12 I noticed the documentation states that
>> recovery targets are not valid when standby.signal is present.
>>
>> But surely the exception is recovery_target_timeline? My testing
>> confirms that this works just as in prior versions with standy_mode=on.
>
> Or maybe we should move recovery_target_timeline to a different section?
> But which one?

Not sure. I think just noting it as an exception is OK, if it is the
only exception. But currently that does not seem to be the case.

> I don't know if recovery_target_timeline is actually useful to change in
> standby mode.

It is. I just dealt with a split-brain case that required the standbys
to be rebuilt on a specific timeline (not latest).

Of course, you could do recovery on that timeline, shutdown, and then
bring the cluster back up as a standby, but that seems like a lot of
extra work.

But as Fujii noted and I've demonstrated in the follow-up pretty much
all target options are allowed for standby recovery. I don't think that
makes sense, personally, but apparently it was allowed in prior versions
so we'll need to think carefully before disallowing it.

--
-David
david(at)pgmasters(dot)net