[Gluster-devel] Handling locks in NSR

[Atin Mukherjee]

-Atin
Sent from one plus one
On 02-Mar-2016 1:40 pm, "Avra Sengupta" <asengupt at redhat.com> wrote:
>
> Hi,
>
> All fops in NSR, follow a specific workflow as described in this UML(
https://docs.google.com/presentation/d/1lxwox72n6ovfOwzmdlNCZBJ5vQcCaONvZva0aLWKUqk/edit?usp=sharing).
However all locking fops will follow a slightly different workflow as
described below. This is a first proposed draft for handling locks, and we
would like to hear your concerns and queries regarding the same.
>
> 1. On receiving the lock, the leader will Journal the lock himself, and
then try to actually acquire the lock. At this point in time, if it fails
to acquire the lock, then it will invalidate the journal entry, and return
a -ve ack back to the client. However, if it is successful in acquiring the
lock, it will mark the journal entry as complete, and forward the fop to
the followers.
>
> 2. The followers on receiving the fop, will journal it, and then try to
actually acquire the lock. If it fails to acquire the lock, then it will
invalidate the journal entry, and return a -ve ack back to the leader. If
it is successful in acquiring the lock, it will mark the journal entry as
complete,and send a +ve ack to the leader.
>
> 3. The leader on receiving all acks, will perform a quorum check. If
quorum meets, it will send a +ve ack to the client. If the quorum fails, it
will send a rollback to the followers.
>
> 4. The followers on receiving the rollback, will journal it first, and
then release the acquired lock. It will update the rollback entry in the
journal as complete and send an ack to the leader.
>
> 5. The leader on receiving the rollback acks, will journal it's own
rollback, and then release the acquired lock. It will update the rollback
entry in the journal, and send a -ve ack to the client.
>
> Few things to be noted in the above workflow are:
> 1. It will be a synchronous operation, across the replica volume.
Is this true with existing replication mechanism?
> 2. Reconciliation will take care of nodes who have missed out the locks.
> 3. On a client disconnect, there will be a lock-timeout on whose
expiration all locks held by that particular client will be released.
>
> Regards,
> Avra
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