+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 <ihrac...@redhat.com> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > 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@lists.openstack.org >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >> > -----BEGIN PGP SIGNATURE----- > Version: GnuPG/MacGPG2 v2.0.22 (Darwin) > Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ > > iQEcBAEBCgAGBQJTv9LHAAoJEC5aWaUY1u57d2cIAIAthLuM6qxN9fVjPwoICEae > oSOLvaDNPpZ+xBBqKI+2l5aFiBXSkHzgCfWGHEZB4e+5odAzt8r3Dg5eG/hwckGt > iZLPGLxcmvD5K0cRoSSPWkPC4KkOwKw0yQHl/JQarDcHQlLgO64jx3bzlB1LDxRu > R/Bvqo1SBo8g/cupWyxJXNViu9z7zAlvcHLRg4j/AfNTsTDZRrSgbMF2/gLTMvN2 > FPtkjBvZq++zOva5G5/TySr1b3QRBFCG0uetVbcVF//90XOw+O++rUiDW1v7vkA9 > OS2sCIXmx1i8kt9yuvs0h11MS8qfX9rSXREJXyPq6NDmePdQdKFsozMdTmqaDfU= > =JfiC > -----END PGP SIGNATURE----- > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
