#26935: DB connections stuck in closed state when using Django ORM in daemon
----------------------------------------------+--------------------
Reporter: noky | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
----------------------------------------------+--------------------
'''Situation:'''
1. A long-running daemon process is using the Django ORM
2. The underlying database gets restarted, causing existing db
connection(s) to become invalid
'''Problem:'''
A subsequent db read using the ORM fail with the exception:
{{{
File "main.py", line 22, in <module>
testread()
File "main.py", line 14, in testread
user = User.objects.all()[0]
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 297, in __getitem__
return list(qs)[0]
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 1074, in _fetch_all
self._result_cache = list(self.iterator())
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 52, in __iter__
results = compiler.execute_sql()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/sql/compiler.py", line 848, in execute_sql
cursor.execute(sql, params)
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/utils.py", line 95, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
OperationalError: terminating connection due to administrator command
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.
}}}
Further subsequent db reads using the ORM yield a different (yet
consistent) exception:
{{{
File "main.py", line 22, in <module>
testread()
File "main.py", line 14, in testread
user = User.objects.all()[0]
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 297, in __getitem__
return list(qs)[0]
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 258, in __iter__
self._fetch_all()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 1074, in _fetch_all
self._result_cache = list(self.iterator())
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/query.py", line 52, in __iter__
results = compiler.execute_sql()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/models/sql/compiler.py", line 846, in execute_sql
cursor = self.connection.cursor()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/base/base.py", line 233, in cursor
cursor = self.make_cursor(self._cursor())
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/base/base.py", line 206, in _cursor
return self.create_cursor()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/utils.py", line 95, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/base/base.py", line 206, in _cursor
return self.create_cursor()
File "/home/noky/Downloads/django-standalone/venv/local/lib/python2.7
/site-packages/django/db/backends/postgresql/base.py", line 210, in
create_cursor
cursor = self.connection.cursor()
InterfaceError: connection already closed
}}}
'''Environment:'''
* Ubuntu 14.04
* PostgreSQL 9.5
* Django 1.9.8
* psycopg2 2.6.2
'''To reproduce problem:'''
* Download attached project files and untar
* Create a PostgreSQL database `testdb`
* Edit `settings.py` to setup db settings
* Run `setup.sh` to create virtualenv, install Django and run the "daemon"
* The daemon simply writes a record to the db, then constantly queries the
db using the Django ORM. Every 5 seconds, a db query is made and the
result is printed
* Stop PostgreSQL and restart it: `sudo service postgresql restart`
* The daemon application will fail to reconnect to the database and the
above exceptions will be output
* It is interesting to note that if you modify the daemon process to
write to the db in it's main loop, the problem does not manifest
(uncomment the `testwrite()` line in `main.py` to see this behavior).
'''Workaround:'''
I have come up with the following patch to workaround the problem, though
it is PostgreSQL specific (it makes use of the `connection.closed`
attribute unique to psycopg). Not sure of a general fix for this problem.
{{{
--- django/db/backends/base/base.py.orig 2016-07-22
15:30:36.655291625 -0400
+++ django/db/backends/base/base.py 2016-07-22 15:37:03.419337590
-0400
@@ -197,6 +197,9 @@
if self.connection is None:
with self.wrap_database_errors:
self.connect()
+ elif self.connection.closed:
+ with self.wrap_database_errors:
+ self.connect()
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/26935>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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