Re: post-freeze damage control

On 4/13/24 01:03, David Steele wrote:
> On 4/12/24 22:12, Tomas Vondra wrote:
>> On 4/11/24 23:48, David Steele wrote:
>>> On 4/11/24 20:26, Tomas Vondra wrote:
>>>
>>>> FWIW that discussion also mentions stuff that I think the feature
>>>> should
>>>> not do. In particular, I don't think the ambition was (or should be) to
>>>> make pg_basebackup into a stand-alone tool. I always saw pg_basebackup
>>>> more as an interface to "backup steps" correctly rather than a complete
>>>> backup solution that'd manage backup registry, retention, etc.
>>>
>>> Right -- this is exactly my issue. pg_basebackup was never easy to use
>>> as a backup solution and this feature makes it significantly more
>>> complicated. Complicated enough that it would be extremely difficult for
>>> most users to utilize in a meaningful way.
>>
>> Perhaps, I agree we could/should try to do better job to do backups, no
>> argument there. But I still don't quite see why introducing such
>> infrastructure to "manage backups" should be up to the patch adding
>> incremental backups. I see it as something to build on top of
>> pg_basebackup/pg_combinebackup, not into those tools.
> 
> I'm not saying that managing backups needs to be part of pg_basebackup,
> but I am saying without that it is not a complete backup solution.
> Therefore introducing advanced features that the user then has to figure
> out how to manage puts a large burden on them. Implementing
> pg_combinebackup inefficiently out of the gate just makes their life
> harder.
> 

I agree with this in general, but I fail to see how it'd be the fault of
this patch. It merely extends what pg_basebackup did before, so if it's
not a complete solution now, it wasn't a complete solution before.

Sure, I 100% agree it'd be great to have a more efficient
pg_combinebackup with fewer restrictions. But if we make these
limitations clear, I think it's better to have this than having nothing.

>>> But they'll try because it is a new pg_basebackup feature and they'll
>>> assume it is there to be used. Maybe it would be a good idea to make it
>>> clear in the documentation that significant tooling will be required to
>>> make it work.
>>
>> Sure, I'm not against making it clearer pg_combinebackup is not a
>> complete backup solution, and documenting the existing restrictions.
> 
> Let's do that then. I think it would make sense to add caveats to the
> pg_combinebackup docs including space requirements, being explicit about
> the format required (e.g. plain), and also possible mitigation with COW
> filesystems.
> 

OK. I'll add this as an open item, for me and Robert.


regards

-- 
Tomas Vondra
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