Re: [proposal] recovery_target "latest"

From: Grigory Smolkin <g(dot)smolkin(at)postgrespro(dot)ru>
To: pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: [proposal] recovery_target "latest"
Date: 2019-11-06 23:28:39
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On 11/6/19 1:55 PM, Grigory Smolkin wrote:
> On 11/6/19 12:56 PM, Fujii Masao wrote:
>> On Wed, Nov 6, 2019 at 6:33 PM Grigory Smolkin
>> <g(dot)smolkin(at)postgrespro(dot)ru> wrote:
>>> On 11/6/19 10:39 AM, Peter Eisentraut wrote:
>>>> This seems to also be related to this discussion:
>>>> <>
>>> Yes, in a way. Strengthening current lax recovery behavior is a very
>>> good idea.
>>>> I like this idea.
>>>> I don't like the name "latest".  What does that mean?  Other
>>>> documentation talks about the "end of the archive".  What does that
>>>> mean?  It means until restore_command errors.  Let's think of a name
>>>> that reflects that better.  Maybe "all_archive" or something like
>>>> that.
>>> As with "immediate", "latest" reflects the latest possible state this
>>> PostgreSQL instance can achieve when using PITR. I think it is simple
>>> and easy to understand for an end user, which sees PITR as a way to go
>>> from one state to another. In my experience, at least, which is, of
>>> course, subjective.
>>> But if we want an argument name to be technically accurate, then, I
>>> think, something like "end-of-available-WAL"/"all-WAL", "end-of-WAL" is
>>> a way to go.
>> 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.

> The other way around, as I see it, is to define RECOVERY_TARGET_LATEST
> as something more complex, for example, the latest possible endptr in
> latest WAL segment. But it is tricky, because WAL archive may keeps
> growing as recovery is progressing or, in case of standby, master
> keeps sending more and more WAL.
>> Regards,
Grigory Smolkin
Postgres Professional:
The Russian Postgres Company

Attachment Content-Type Size
0003-recovery_target_latest.patch text/x-patch 9.0 KB

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