Re: [pbs-devel] [PATCH proxmox-backup v3 1/3] fix #6195: api: datastore: add endpoint for moving namespaces

[Hannes Laimer <h.laimer@proxmox.com>]

On 15.09.25 10:15, Christian Ebner wrote:
> Thanks for having a go at this issue, I did not yet have an in depth 
> look at this but unfortunately I'm afraid the current implementation 
> approach will not work for the S3 backend (and might also have issues 
> for local datastores).
> 
> Copying the S3 objects is not an atomic operation and  will take some 
> time, so leaves you open for race conditions. E.g. while you copy 
> contents, a new backup snapshot might be created in one of the already 
> copied backup groups, which will then however be deleted afterwards. 
> Same is true for pruning, and other metadata editing operations such as
> adding notes, backup task logs, ecc.
> 

Yes, but not really. We lock the `active_operations` tracking file, so
no new read/write operations can be started after we start the moving
process. There's a short comment in the API endpoint function.

I'm not sure there is much value in more granular locking, I mean, is
half a successful move worth much? Unless we add some kind of rollback,
but tbh, I feel like that would not be worth the effort I think.

> So IMO this must be tackled on a group level, making sure to get an 
> exclusive lock for each group (on the source as well as target of the 
> move operation) before doing any manipulation. Only then it is okay to 
> do any non-atomic operations.
> 
> The moving of the namespace must then be implemented as batch operations 
> on the groups and sub-namespaces.
> 
> This should be handled the same also for regular datastores, to avoid 
> any races there to.



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