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
30441	Connection leak if CONN_MAX_AGE == None	cryptogun	nobody	"PostgreSQL default max connection is 100.   
if `CONN_MAX_AGE == None` in setting.py:
Every time I authenticate() a user, the connection is opened but not closed.
{{{user = authenticate(request=request, username='admin', password='123456')}}}

if `CONN_MAX_AGE == 0`:
The connection will be closed properly.

{{{
Traceback (most recent call last):
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\utils\autoreload.py"", line 225, in wrapper
    fn(*args, **kwargs)
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\management\commands\runserver.py"", line 120, in inner_run
    self.check_migrations()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\core\management\base.py"", line 442, in check_migrations
    executor = MigrationExecutor(connections[DEFAULT_DB_ALIAS])
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\migrations\executor.py"", line 18, in __init__
    self.loader = MigrationLoader(self.connection)
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\migrations\loader.py"", line 49, in __init__
    self.build_graph()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\migrations\loader.py"", line 212, in build_graph
    self.applied_migrations = recorder.applied_migrations()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\migrations\recorder.py"", line 61, in applied_migrations
    if self.has_table():
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\migrations\recorder.py"", line 44, in has_table
    return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\base\base.py"", line 256, in cursor
    return self._cursor()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\base\base.py"", line 233, in _cursor
    self.ensure_connection()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\base\base.py"", line 217, in ensure_connection
    self.connect()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\utils.py"", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\base\base.py"", line 217, in ensure_connection
    self.connect()
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\base\base.py"", line 194, in connect
    self.connection = self.get_new_connection(conn_params)
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\django\db\backends\postgresql\base.py"", line 178, in get_new_connection
    connection = Database.connect(**conn_params)
  File ""C:\Users\me\AppData\Local\Programs\Python\Python36\lib\site-packages\psycopg2\__init__.py"", line 126, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
django.db.utils.OperationalError: FATAL:  remaining connection slots are reserved for non-replication superuser connections
}}}

Bug reproduce (with attached project):  
1. set CONN_MAX_AGE to None:
{{{
# settings.py
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
        'CONN_MAX_AGE': None,
    }
}
}}}
2. Print and trace db connection:
Modify `site-packages\django\db\backends\base\base.py`
{{{
# site-packages\django\db\backends\base\base.py
# Add a print line:
    def ensure_connection(self):
        """"""Guarantee that a connection to the database is established.""""""
        if self.connection is None:
            with self.wrap_database_errors:
                print('open connection +++++++++++++++++++')
                self.connect()
}}}
{{{
# Add a print line:
    def close(self):
        """"""Close the connection to the database.""""""
        self.validate_thread_sharing()
        self.run_on_commit = []

        # Don't call validate_no_atomic_block() to avoid making it difficult
        # to get rid of a connection in an invalid state. The next connect()
        # will reset the transaction state anyway.
        if self.closed_in_transaction or self.connection is None:
            return
        try:
            print('close connection ......................')
            self._close()
        finally:
            if self.in_atomic_block:
                self.closed_in_transaction = True
                self.needs_rollback = True
            else:
                self.connection = None
}}}
3. Open a new incognito browser <kbd>Ctrl</kbd><kbd>Shift</kbd> + <kbd>n</kbd>.
4. Goto landing page.
5. Check Django log output.  
`open connection +++++++++++++++++++`  
No close log printed.  
6. Goto 3. and try as many times as you want.
7. Switch to PostgreSQL backend, refresh 100 times, and you will get the above `OperationalError`.
  
8. Set CONN_MAX_AGE to `0` in settings.py.
9. Retry 3~5
Now the close was executed.
{{{
open connection +++++++++++++++++++
[04/May/2019 16:09:53] ""GET / HTTP/1.1"" 200 2
close connection ......................
}}}"	Bug	new	Uncategorized	2.2	Normal				Unreviewed	0	0	0	0	0	0