Open Stack

Hi folks,

Currently we use a lockfile to protect the create operations from concurrent delete the source volume/snapshot, we use exclusive
locks on both delete and create sides which will ensure that:


1.       If a create of VolA from snap/VolB is in progress, any delete requests for snap/VolB will wait until the create is complete.

2.       If a delete of snap/VolA is in progress, any create from snap/VolA will wait until snap/VolA delete is complte.

but, the exclusive locks will also result in:


3.       If a create of VolA from snap/VolB is inprogress, any other create requests from snap/VolB will wait until the create is complete.

So the create operations from same volume/snapshot can not process on parallel, please reference bp [1].
I'd like to change the current filelock or introduce a new lock to oslo.concurrency.

Proposed change:
Add exclusive(write) locks for delete operations and shared(read) locks for create operations, to ensure that create from volume/snapshot
can work on parallel and protect create operations from concurrent delete the source volume/snapshot.

I'd like to get what's your suggestions, thanks in advance.

[1] https://blueprints.launchpad.net/cinder/+spec/enhance-locks


-zhenguo
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