Re: [Engine-devel] Requirement for Locking Mechanism

----- Original Message ----- > From: "Yaniv Kaul"<ykaul(a)redhat.com> > To: "Michael Kublin"<mkublin(a)redhat.com> > Cc: engine-devel(a)ovirt.org > Sent: Tuesday, November 29, 2011 12:18:15 PM > Subject: Re: [Engine-devel] Requirement for Locking Mechanism > > 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 >> >> _______________________________________________ >> Engine-devel mailing list >> Engine-devel(a)ovirt.org >> http://lists.ovirt.org/mailman/listinfo/engine-devel > > There's an implicit assumption that there's only going to be a single > active backend working against the database? > Y. > Yes, the backend will lock some entity, until its status will not be updated in db, after that the lock will be released. So, it will solve a race between canDoAction and beginning of execute of the command