Open Stack

+1 here too,

Amazed with the performance gains, x2.4 seems a lot,
and we'd get rid of deadlocks.



----- Original Message -----
> +1
> 
> I'm pretty excited about the possibilities here.  I've had this
> mysqldb/eventlet contention in the back of my mind for some time now.
> I'm glad to see some work being done in this area.
> 
> Carl
> 
> On Fri, Jul 11, 2014 at 7:04 AM, Ihar Hrachyshka <ihrachys at redhat.com> wrote:
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> > On 09/07/14 13:17, Ihar Hrachyshka wrote:
> >> Hi all,
> >>
> >> Multiple projects are suffering from db lock timeouts due to
> >> deadlocks deep in mysqldb library that we use to interact with
> >> mysql servers. In essence, the problem is due to missing eventlet
> >> support in mysqldb module, meaning when a db lock is encountered,
> >> the library does not yield to the next green thread, allowing other
> >> threads to eventually unlock the grabbed lock, and instead it just
> >> blocks the main thread, that eventually raises timeout exception
> >> (OperationalError).
> >>
> >> The failed operation is not retried, leaving failing request not
> >> served. In Nova, there is a special retry mechanism for deadlocks,
> >> though I think it's more a hack than a proper fix.
> >>
> >> Neutron is one of the projects that suffer from those timeout
> >> errors a lot. Partly it's due to lack of discipline in how we do
> >> nested calls in l3_db and ml2_plugin code, but that's not something
> >> to change in foreseeable future, so we need to find another
> >> solution that is applicable for Juno. Ideally, the solution should
> >> be applicable for Icehouse too to allow distributors to resolve
> >> existing deadlocks without waiting for Juno.
> >>
> >> We've had several discussions and attempts to introduce a solution
> >> to the problem. Thanks to oslo.db guys, we now have more or less
> >> clear view on the cause of the failures and how to easily fix them.
> >> The solution is to switch mysqldb to something eventlet aware. The
> >> best candidate is probably MySQL Connector module that is an
> >> official MySQL client for Python and that shows some (preliminary)
> >> good results in terms of performance.
> >
> > I've made additional testing, creating 2000 networks in parallel (10
> > thread workers) for both drivers and comparing results.
> >
> > With mysqldb: 215.81 sec
> > With mysql-connector: 88.66
> >
> > ~2.4 times performance boost, ok? ;)
> >
> > I think we should switch to that library *even* if we forget about all
> > the nasty deadlocks we experience now.
> >
> >>
> >> I've posted a Neutron spec for the switch to the new client in Juno
> >> at [1]. Ideally, switch is just a matter of several fixes to
> >> oslo.db that would enable full support for the new driver already
> >> supported by SQLAlchemy, plus 'connection' string modified in
> >> service configuration files, plus documentation updates to refer to
> >> the new official way to configure services for MySQL. The database
> >> code won't, ideally, require any major changes, though some
> >> adaptation for the new client library may be needed. That said,
> >> Neutron does not seem to require any changes, though it was
> >> revealed that there are some alembic migration rules in Keystone or
> >> Glance that need (trivial) modifications.
> >>
> >> You can see how trivial the switch can be achieved for a service
> >> based on example for Neutron [2].
> >>
> >> While this is a Neutron specific proposal, there is an obvious wish
> >> to switch to the new library globally throughout all the projects,
> >> to reduce devops burden, among other things. My vision is that,
> >> ideally, we switch all projects to the new library in Juno, though
> >> we still may leave several projects for K in case any issues arise,
> >> similar to the way projects switched to oslo.messaging during two
> >> cycles instead of one. Though looking at how easy Neutron can be
> >> switched to the new library, I wouldn't expect any issues that
> >> would postpone the switch till K.
> >>
> >> It was mentioned in comments to the spec proposal that there were
> >> some discussions at the latest summit around possible switch in
> >> context of Nova that revealed some concerns, though they do not
> >> seem to be documented anywhere. So if you know anything about it,
> >> please comment.
> >>
> >> So, we'd like to hear from other projects what's your take on that
> >> move, whether you see any issues or have concerns about it.
> >>
> >> Thanks for your comments, /Ihar
> >>
> >> [1]: https://review.openstack.org/#/c/104905/ [2]:
> >> https://review.openstack.org/#/c/105209/
> >>
> >> _______________________________________________ OpenStack-dev
> >> mailing list OpenStack-dev at lists.openstack.org
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