Re: [proposal] recovery_target "latest"

At Thu, 7 Nov 2019 12:22:28 +0300, Grigory Smolkin <g(dot)smolkin(at)postgrespro(dot)ru> wrote in
>
> On 11/7/19 8:36 AM, Kyotaro Horiguchi wrote:
> > At Thu, 7 Nov 2019 02:28:39 +0300, Grigory Smolkin
> > <g(dot)smolkin(at)postgrespro(dot)ru> wrote in
> >> On 11/6/19 1:55 PM, Grigory Smolkin wrote:
> >>> On 11/6/19 12:56 PM, Fujii Masao wrote:
> >>>> What happens if this parameter is set to latest in the standby mode?
> >>>> Or the combination of those settings should be prohibited?
> >>>
> >>> Currently it will behave just like regular standby, so I think, to
> >>> avoid confusion and keep things simple, the combination of them should
> >>> be prohibited.
> >>> Thank you for pointing this out, I will work on it.
> >> Attached new patch revision, now it is impossible to use
> >> recovery_target 'latest' in standby mode.
> >> TAP test is updated to reflect this behavior.
> > In the first place, latest (or anything it could be named as) is
> > defined as the explit label for the default behavior. Thus the latest
> > should work as if nothing is set to recovery_target* following the
> > definition. That might seems somewhat strange but I think at least it
> > is harmless.
>
>
> Well, it was more about getting default behavior by using some
> explicit recovery_target, not the other way around. Because it will
> break some 3rd party backup and replication applications, that may
> rely on old behavior of ignoring recovery_target_action when no
> recovery_target is provided.
> But you think that it is worth pursuing, I can do that.

Ah. Sorry for the misleading statement. What I had in my mind was
somewhat the mixture of them. I thought that recovery_target =''
behaves the same way as now, r_t_action is ignored. And 'latest' just
makes recovery_target_action work as the current non-empty
recovery_target's does. But I'm not confident that it is a good
design.

> > recovery_target=immediate + r_t_action=shutdown for a standby works as
> > commanded. Do we need to inhibit that, too?
>
> Why something, that work as expected, should be inhibited?

To make sure, I don't think we should do that. I meant by the above
that standby mode is already accepting recovery_target_action so
inhibiting that only for 'latest' is not orthogonal and could be more
confusing for users, and complicatig the code. So my opinion is we
shouldn't inhibit 'latest' unless r_t_action harms.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center