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@pgmasters.net