[Engine-devel] Requirement for Locking Mechanism

[Yaniv Kaul]

On 11/29/2011 12:13 PM, Michael Kublin wrote:
> Hi All,
>
> We are introducing a new short term locking mechanism at engine.
> The motivation is races which are occurring between different flows, the main problem is :
> we did not update status of some entity and other flow was started , which is a main cause for different collisions and situation which
> can not be fixed in appropriate way by engine or vdsm.
> The current status is a workaround which is trying to reduce a race : in many places in the code, there is additional query to DB in order to check the appropriate status of entity.
> The proposed solution is internal locking mechanism - which will lock an appropriate entity until its status will not be updated in DB, after that
> an internal short term lock will be released.
>
> The design for locking mechanism can be found here: http://www.ovirt.org/wiki/Features/DetailedLockMechanism

The page still has many remains of the template.

> The patch which is introduce an implementation for mechanism can be found here: http://gerrit.ovirt.org/#change,403
> (Using of new mechanism all around a code and integration with bll will be sent in the future, including cleaning of workaround)
>
> Regards Michael
>
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There's an implicit assumption that there's only going to be a single 
active backend working against the database?
Y.