Django + OS X + MySQL + first session variable retrieval = crash - mysql

Question

Am experienced with Django, Apache, WSGI, MySql, etc. and have this environment setup and working fine on another OS X computer running Lion. Django session backend is db, session middleware and app are both enabled properly in settings. During first request of site view, we set a request.session key/value, which this first time thru works fine. On subsequent view though when we check if the key/value exists, we get a server-level 500 error that even with Debug mode on doesn't make it to the python interpreter to generate a full stack trace exception. The apache log generates the following messages...
[Mon Apr 16 14:26:22 2012] [notice] Apache/2.2.21 (Unix) DAV/2 mod_wsgi/3.3 Python/2.7.1 mod_ssl/2.2.21 OpenSSL/0.9.8r configured -- resuming normal operations
[Mon Apr 16 14:26:27 2012] [info] mod_wsgi (pid=2362): Create interpreter 'snap.joe|'.
[Mon Apr 16 14:26:27 2012] [info] [client 127.0.0.1] mod_wsgi (pid=2362, process='snap', application='snap.joe|'): Loading WSGI script '/var/www/venvs/snap_env/snap/wsgi/wsgi.py'.
[Mon Apr 16 14:26:32 2012] [error] [client 127.0.0.1] Premature end of script headers: wsgi.py
[Mon Apr 16 14:26:33 2012] [notice] child pid 2362 exit signal Bus error (10)
Have checked that a MySQL db table django_session row is added properly with session_data and also the cookie set in the browser after the first request contains the proper/matching session_id. If I add a simple request.session.flush() just before the existing session code, we can bypass the error obviously because there is never anything in the session. One more thing, the value we are adding to the session key/value store is a Django QuerySet object. Again, this is working on a live CentOS server, and also another Mac OS X Lion machine (albeit running Python 2.6 instead of 2.7).
Any ideas folks? Many thanks!

Answer 1

See documented reasons at:
http://code.google.com/p/modwsgi/wiki/FrequentlyAskedQuestions#Apache_Process_Crashes
and follow further links for possible workarounds.
In short, can be shared library version conflict, using mod_python at same time, or extension module for Python that doesn't work with sub interpreter.
If this is only Python site on that Apache, set:
WSGIApplicationGroup %{GLOBAL}
for one potential quick solution.

Answer 2

A few thoughts:
1) are you running the same versions of modules? Django just recently updated (1.4), so if you did a pip install and didn't specify a version your production might have an older version while your development has the newer one.
2) Can you test this using just the manage.py runserver? My suspicions are that it's something to do with the apache config (so if it works fine in runserver, that means the issue is with apache).