id summary reporter owner description type status component version severity resolution keywords cc stage has_patch needs_docs needs_tests needs_better_patch easy ui_ux 13214 Random OperationalError when using FastCGI (+ possible solutions) Henrique C. Alves nobody "Possible solution: http://groups.google.com/group/django-users/browse_thread/thread/2c7421cdb9b99e48 > Until recently I was curious to test > this on Django 1.1.1. Will this > exception be thrown again... surprise, > there it was again. It took me some > time to debug this, helpful hint was > that it only shows when (pre)forking. > So for those who getting randomly > those exceptions, I can say... fix > your code :) Ok.. seriously, there > are always few ways of doing this, so > let me firs explain where is a > problem first. If you access database > when any of your modules will import > as, e.g. reading configuration from > database then you will get this error. > When your fastcgi-prefork application > starts, first it imports all modules, > and only after this forks children. > If you have established db connection > during import all children processes > will have an exact copy of that > object. This connection is being > closed at the end of request phase > (request_finished signal). So first > child which will be called to process > your request, will close this > connection. But what will happen to > the rest of the child processes? They > will believe that they have open and > presumably working connection to the > db, so any db operation will cause an > exception. Why this is not showing in > threaded execution model? I suppose > because threads are using same object > and know when any other thread is > closing connection. How to fix this? > Best way is to fix your code... but > this can be difficult sometimes. > Other option, in my opinion quite > clean, is to write somewhere in your > application small piece of code: {{{ from django.db import connection from django.core import signals def close_connection(**kwargs): connection.close() signals.request_started.connect(close_connection) }}} Not ideal thought, connecting twice to the DB is a workaround at best. ---------- Possible solution: using connection pooling (pgpool, pgbouncer), so you have DB connections pooled and stable, and handed fast to your FCGI daemons. The problem is that this triggers another bug, psycopg2 raising an *InterfaceError* because it's trying to disconnect twice (pgbouncer already handled this). Now the culprit is Django signal *request_finished* triggering *connection.close()*, and failing loud even if it was already disconnected. I don't think this behavior is desired, as if the request already finished, we don't care about the DB connection anymore. A patch for correcting this should be simple. The relevant traceback: {{{ /usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/core/handlers/wsgi.py in __call__(self=, environ={'AUTH_TYPE': 'Basic', 'DOCUMENT_ROOT': '/storage/test', 'GATEWAY_INTERFACE': 'CGI/1.1', 'HTTPS': 'off', 'HTTP_ACCEPT': 'application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5', 'HTTP_ACCEPT_ENCODING': 'gzip, deflate', 'HTTP_AUTHORIZATION': 'Basic dGVzdGU6c3VjZXNzbw==', 'HTTP_CONNECTION': 'keep-alive', 'HTTP_COOKIE': '__utma=175602209.1371964931.1269354495.126938948...none); sessionid=a1990f0d8d32c78a285489586c510e8c', 'HTTP_HOST': 'www.rede-colibri.com', ...}, start_response=) 246 response = self.apply_response_fixes(request, response) 247 finally: 248 signals.request_finished.send(sender=self.__class__) 249 250 try: global signals = , signals.request_finished = , signals.request_finished.send = >, sender undefined, self = , self.__class__ = /usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/dispatch/dispatcher.py in send(self=, sender=, **named={}) 164 165 for receiver in self._live_receivers(_make_id(sender)): 166 response = receiver(signal=self, sender=sender, **named) 167 responses.append((receiver, response)) 168 return responses response undefined, receiver = , signal undefined, self = , sender = , named = {} /usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/db/__init__.py in close_connection(**kwargs={'sender': , 'signal': }) 63 # when a Django request is finished. 64 def close_connection(**kwargs): 65 connection.close() 66 signals.request_finished.connect(close_connection) 67 global connection = , connection.close = > /usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/db/backends/__init__.py in close(self=) 74 def close(self): 75 if self.connection is not None: 76 self.connection.close() 77 self.connection = None 78 self = , self.connection = , self.connection.close = }}} Exception handling here could add more leniency: {{{ **/usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/db/__init__.py** 63 # when a Django request is finished. 64 def close_connection(**kwargs): 65 connection.close() 66 signals.request_finished.connect(close_connection) }}} Or it could be handled better on psycopg2, so to not throw fatal errors if all we're trying to do is disconnect and it already is: {{{ **/usr/local/lib/python2.6/dist-packages/Django-1.1.1-py2.6.egg/django/db/backends/__init__.py** 74 def close(self): 75 if self.connection is not None: 76 self.connection.close() 77 self.connection = None }}} Other than that, I'm short on ideas. Not sure if this is supposed to be fixed on 1.2, maybe multi-db support refactored things and dealt with this issue. I'll try testing with a 1.2 enviro. " closed Core (Other) 1.1 invalid hcarvalhoalves@… Unreviewed 0 0 0 0 0 0