Perform snapshot indexing with --no-lock to prevent issues if repo is in use when re-indexing

[sumnerboy12]

I assume that when clicking "Index Snapshots" all you are doing is calling restic snapshots to retrieve the repo snapshot history.

This can be done with the --no-lock argument which does a read-only "look" at the repo and means if anything else has a lock on the repo, the index operation will still complete.

[garethgeorge]

It’s an interesting idea— I think this could make sense for backrest. What are the downsides of no lock on system task execution?

I assume we can get inconsistent reads at some points but that may not be an issue.

[sumnerboy12]

I would only think you can use it for readonly operations - i.e. indexing snapshots etc. It just means if there is a backup operation in-progress the snapshot indexing will still complete (although it might not be 100% accurate if the backup finishes etc).

Possibly also useful when calculating stats.