x
/
gantt
Code Issues Proposed changes

Added docs on MySQL queries blocking main thread. 

Added to the RST docs to describe how queries to MySQL will block a nova
service.

Change-Id: I4ae209e2827978cc5469162d386197f2e46b342d
This commit is contained in:
Lorin Hochstein 2012-03-02 09:39:36 -05:00
parent cb1f66f5d9
commit 2438389c75
3 changed files with 42 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
.mailmap
View File

@ -38,6 +38,7 @@
<josh@jk0.org> <josh.kearney@rackspace.com>
<justin@fathomdb.com> <justinsb@justinsb-desktop>
<justin@fathomdb.com> <superstack@superstack.org>
<lorin@nimbisservices.com> <lorin@isi.edu>
<masumotok@nttdata.co.jp> Masumoto<masumotok@nttdata.co.jp>
<masumotok@nttdata.co.jp> <root@openstack2-api>
<matt.dietz@rackspace.com> <matthewdietz@Matthew-Dietzs-MacBook-Pro.local>

2
Authors
View File

@ -112,7 +112,7 @@ Koji Iida <iida.koji@lab.ntt.co.jp>
Liam Kelleher <liam.kelleher@hp.com>
Likitha Shetty <likitha.shetty@citrix.com>
Loganathan Parthipan <parthipan@hp.com>
Lorin Hochstein <lorin@isi.edu>
Lorin Hochstein <lorin@nimbisservices.com>
Lvov Maxim <usrleon@gmail.com>
Mandell Degerness <mdegerne@gmail.com>
Mark McLoughlin <markmc@redhat.com>

34
doc/source/devref/threading.rst
View File

@ -14,4 +14,38 @@ The use of green threads reduces the likelihood of race conditions, but does
not completely eliminate them. In some cases, you may need to use the
``@utils.synchronized(...)`` decorator to avoid races.
In addition, since there is only one operating system thread, a call that
blocks that main thread will block the entire process.
Yielding the thread in long-running tasks
-----------------------------------------
If a code path takes a long time to execute and does not contain any methods
that trigger an eventlet context switch, the long-running thread will block
any pending threads.
This scenario can be avoided by adding calls to the eventlet sleep method
in the long-running code path. The sleep call will trigger a context switch
if there are pending threads, and using an argument of 0 will avoid introducing
delays in the case that there is only a single green thread::
from eventlet import greenthread
...
greenthread.sleep(0)
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.
The Diablo release contained a thread-pooling implementation that did not
block, but this implementation resulted in a `bug`_ and was removed.
See this `mailing list thread`_ for a discussion of this issue, including
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