PyMongo and mod_wsgi¶
To run your application under mod_wsgi, follow these guidelines:
Run
mod_wsgi
in daemon mode with theWSGIDaemonProcess
directive.Assign each application to a separate daemon with
WSGIProcessGroup
.Use
WSGIApplicationGroup %{GLOBAL}
to ensure your application is running in the daemon’s main Python interpreter, not a sub interpreter.
For example, this mod_wsgi
configuration ensures an application runs in the
main interpreter:
<VirtualHost *>
WSGIDaemonProcess my_process
WSGIScriptAlias /my_app /path/to/app.wsgi
WSGIProcessGroup my_process
WSGIApplicationGroup %{GLOBAL}
</VirtualHost>
If you have multiple applications that use PyMongo, put each in a separate daemon, still in the global application group:
<VirtualHost *>
WSGIDaemonProcess my_process
WSGIScriptAlias /my_app /path/to/app.wsgi
<Location /my_app>
WSGIProcessGroup my_process
</Location>
WSGIDaemonProcess my_other_process
WSGIScriptAlias /my_other_app /path/to/other_app.wsgi
<Location /my_other_app>
WSGIProcessGroup my_other_process
</Location>
WSGIApplicationGroup %{GLOBAL}
</VirtualHost>
Background: mod_wsgi
can run in “embedded” mode when only WSGIScriptAlias
is set, or “daemon” mode with WSGIDaemonProcess. In daemon mode, mod_wsgi
can run your application in the Python main interpreter, or in sub interpreters.
The correct way to run a PyMongo application is in daemon mode, using the main
interpreter.
Python C extensions in general have issues running in multiple
Python sub interpreters. These difficulties are explained in the documentation for
Py_NewInterpreter
and in the Multiple Python Sub Interpreters
section of the mod_wsgi
documentation.
Beginning with PyMongo 2.7, the C extension for BSON detects when it is running
in a sub interpreter and activates a workaround, which adds a small cost to
BSON decoding. To avoid this cost, use WSGIApplicationGroup %{GLOBAL}
to
ensure your application runs in the main interpreter.
Since your program runs in the main interpreter it should not share its process with any other applications, lest they interfere with each other’s state. Each application should have its own daemon process, as shown in the example above.