-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 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 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/ -----BEGIN PGP SIGNATURE----- Version: GnuPG/MacGPG2 v2.0.22 (Darwin) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCgAGBQJTvSS+AAoJEC5aWaUY1u57uk0IAMNIW4e59fU8uiF7eg8KwIgU 5vjzDP4GX454Oxm0h5q3Olc0nXIeB6zSBGDoomgLk9+4AS250ihGRA/V10iDEJTF yubcvknep/ZfF+lKkmgBA3WNXJgTXffXeN2bimC6t5zJA+8Cmn3lUPu0djt0GWs7 AktufkPbVj7ZauN6w9OpW4AnoZX1fARvynCilTuHYu+lb8nQ/Hatqu5dgqdeDyRp jodLoN1ow3VYR7Cq5jocqhw719aiKLJdlUgWVHNL5A5oTR1Uxu0AdleeUzXVUvFm +EQO0Xe+slMSBgzBsgPJAiX0Vkc6kfJdFHR571QUWCXaXF1nUEIkgra/7j+0Uqs= =bgds -----END PGP SIGNATURE----- _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
