When running Python inside PostgreSQL using plpython on OSX 10.7.5 I started coming across very strange and apparently random ImportErrors. For example, failing to find the stat module while importing site:

     Traceback (most recent call last):
       File "/Users/jinty/.buildout/eggs/setuptools-0.6c11-py2.7.egg/site.py", line 73, in <module>
         __boot()
       File "/Users/jinty/.buildout/eggs/setuptools-0.6c11-py2.7.egg/site.py", line 2, in __boot
         import sys, imp, os, os.path
       File "/Users/jinty/src/mp/lib/python2.7/os.py", line 49, in <module>
         import posixpath as path
       File "/Users/jinty/src/mp/lib/python2.7/posixpath.py", line 15, in <module>
         import stat
     ImportError: No module named stat

I debugged this by using PYTHONVERBOSE and modifying import.c with the attached patch. I found that stat.py was not found because fopen() failed with "Too many open files". There were not enough open files because OSX has insanely low limits and PostgreSQL was using a large chunk of that. ulimit -n 4096 resolved the errors. I spent a LOT of time trying to figure that out (see the thread at http://www.postgresql.org/message-id/20130114163014.GA600@Brians-MacBook-Air.local).

The bug I wish to report is that the real error (Too many open files) is hidden by "ImportError: No module named stat". For anyone who does not want to modify import.c and rebuild python, it is almost impossible to figure out what is really happening.