-----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
