Fix for #359 MySQL-OperationalError (#370)

When the database connection dies (database server crash), the database scheduler of djcelery doesn't close the broken connection for its scheduler update calls. Every 5 seconds an OperationalError: (2006, 'MySQL server has gone away') occurs.

This patches checks the database connection when a DATABASE_ERROR occurs and closes the connection when necessary. The database scheduler reconnects automatically on the next try.

Author: trunneml

djcelery/schedulers.py

@@ -182,6 +182,8 @@ def schedule_changed(self):
 
             last, ts = self._last_timestamp, self.Changes.last_change()
         except DATABASE_ERRORS as exc:
+            # Close the connection when it is broken
+            transaction.get_connection().close_if_unusable_or_obsolete()
             error('Database gave error: %r', exc, exc_info=1)
             return False
         try: