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

[Christian Ebner <c.ebner@proxmox.com>]

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.

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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