diff --git a/doc/source/threading.rst b/doc/source/threading.rst
index 8fbc973172ed..3836ff610c99 100644
--- a/doc/source/threading.rst
+++ b/doc/source/threading.rst
@@ -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