openstack/nova
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Merge "Adjust MySQL access with eventlet"

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Jenkins 2016-07-27 14:14:43 +00:00 committed by Gerrit Code Review
commit 953514c4b2
1 changed files with 6 additions and 4 deletions
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10
doc/source/threading.rst
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@ -38,10 +38,11 @@ contributors use ``greenthread.sleep()`` instead of ``time.sleep()``.
MySQL access and eventlet
-------------------------
Queries to the MySQL database will block the main thread of a service. This is
because OpenStack services use an external C library for accessing the MySQL
database. Since eventlet cannot use monkey-patching to intercept blocking
calls in a C library, the resulting database query blocks the thread.
There are some MySQL DB API drivers for oslo.db, like `PyMySQL`_, MySQL-python
etc. PyMySQL is the default MySQL DB API driver for oslo.db, and it works well with
eventlet. MySQL-python uses an external C library for accessing the MySQL database.
Since eventlet cannot use monkey-patching to intercept blocking calls in a C library,
so queries to the MySQL database will block the main thread of a service.
The Diablo release contained a thread-pooling implementation that did not
block, but this implementation resulted in a `bug`_ and was removed.
@ -52,3 +53,4 @@ a discussion of the `impact on performance`_.
.. _bug: https://bugs.launchpad.net/nova/+bug/838581
.. _mailing list thread: https://lists.launchpad.net/openstack/msg08118.html
.. _impact on performance: https://lists.launchpad.net/openstack/msg08217.html
.. _PyMySQL: https://wiki.openstack.org/wiki/PyMySQL_evaluation