Hi all,
We are using django (1.3) with django-celery (2.2.4), database in
postgres (9.0.1) with psycopg2 (2.2.2) connector for a large project
(also large company).
Executing celery tasks one by one works fine. When requested, django
inserts a new row in db (django starts a transaction) and two task and
are invoked and both tasks write in the same row but in different
fields. With CELERY_ALWAYS_EAGER set, the tasks execute sequentially.
The problem comes when switching celery from synchronous to
asynchronous. Executing the same code, the celery daemon raises this
exception:
[2011-05-13 15:37:51,981: WARNING/PoolWorker-1] /prj/env/lib/python2.6/
site-packages/celery/worker/job.py:114: UserWarning: Exception outside
body: <class 'psycopg2.OperationalError'>: no connection to the server
[2011-05-13 15:37:51,982: ERROR/MainProcess] Task
cds.tasks.resize[2f198cdd-a1d5-4e61-b4cd-a69a8e6586f4] raised
exception: OperationalError('no connection to the server\n',)
Traceback (most recent call last):
File "/prj/env/lib/python2.6/site-packages/celery/worker/job.py",
line 108, in execute_safe
return self.execute(*args, **kwargs)
File "/prj/env/lib/python2.6/site-packages/celery/worker/job.py",
line 126, in execute
return super(WorkerTaskTrace, self).execute()
File "/prj/env/lib/python2.6/site-packages/celery/execute/trace.py",
line 76, in execute
retval = self._trace()
File "/prj/env/lib/python2.6/site-packages/celery/execute/trace.py",
line 92, in _trace
return handler(trace.retval, trace.exc_type, trace.tb,
trace.strtb)
File "/prj/env/lib/python2.6/site-packages/celery/worker/job.py",
line 147, in handle_failure
exc = self.task.backend.mark_as_failure(self.task_id, exc, strtb)
File "/prj/env/lib/python2.6/site-packages/celery/backends/base.py",
line 45, in mark_as_failure
traceback=traceback)
File "/prj/env/lib/python2.6/site-packages/celery/backends/base.py",
line 157, in store_result
return self._store_result(task_id, result, status, traceback,
**kwargs)
File "/prj/env/lib/python2.6/site-packages/djcelery/backends/
database.py", line 20, in _store_result
traceback=traceback)
File "/prj/env/lib/python2.6/site-packages/djcelery/managers.py",
line 46, in _inner
transaction.rollback_unless_managed()
File "/prj/env/lib/python2.6/site-packages/django/db/
transaction.py", line 133, in rollback_unless_managed
connection.rollback_unless_managed()
File "/prj/env/lib/python2.6/site-packages/django/db/backends/
__init__.py", line 193, in rollback_unless_managed
self._rollback()
File "/prj/env/lib/python2.6/site-packages/django/db/backends/
__init__.py", line 50, in _rollback
return self.connection.rollback()
OperationalError: no connection to the server
For testing and isolate the problem, we tried with MySQL (5.1.49) and
mysql-django (1.2.3). Just changed db connector and port, and worked
like charm (no fails over ~400 tasks).
We also have tried modifying celery parameters (CELERY_DB_REUSE_MAX,
CELERY_TASK_PUBLISH_RETRY mainly) with some code tweaks.
After a couple of hours, we found the best fix-approach, wich has
minimized the number of exception, but still fails.
http://thebuild.com/blog/2010/10/25/django-and-postgresql-idle-in-transaction-connections/
Even with the auto commit enabled. Anyway, we don't want to change
django code.
We believe it's a connector problem, just google a little and you will
find lots a posts with same/similar problem.
Some other useful info/samples:
http://stackoverflow.com/questions/1303654/threaded-django-task-doesnt-automatically-handle-transactions-or-db-connections
http://groups.google.com/group/django-developers/browse_frm/thread/5249b9ba993431ca/4d1b9d65329c8b75
http://code.djangoproject.com/ticket/9964
Can you give any light on this? If we don't find any solution, we'll
move to mysql, which by now seems to be the best (extreme as well)
option.
Otto Vazquez
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