It is very common problem and been covered at the pooling doc. You may take
a look
at
http://docs.sqlalchemy.org/en/latest/core/pooling.html#disconnect-handling-pessimistic
Personally, I don't use connection pool for celery task. Since the task is
often long running and only need one connection to DB.
Best,
Rick
On Saturday, June 20, 2015 at 2:15:54 PM UTC+8, Rohitash Kumar wrote:
>
> My current setup include
>
> Flask, Flask-SQLAlchemy, celery
>
> Now the problem which I am running into is sometimes database queries
> inside celery tasks gives stale data i.e If I ask for last record from
> table I get second last while the last entry was inserted just 10-15
> minutes before doing the query and sometimes I see exceptions like these.
>
> OperationalError("(OperationalError) (2006, \'MySQL server has gone
> away\')",)'
>
> Following is another traceback
>
> File "/home/sys_user/repo/my_app/app/tasks/reminders.py", line 63, in run
> config = Reminder.query.filter_by(id=reminder_id).first()
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2341, in first
> ret = list(self[0:1])
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2208, in __getitem__
> return list(res)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2412, in __iter__
> return self._execute_and_instances(context)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py",
> line 2427, in _execute_and_instances
> result = conn.execute(querycontext.statement, self._params)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py",
> line 729, in execute
> return meth(self, multiparams, params)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/sql/elements.py",
> line 321, in _execute_on_connection
> return connection._execute_clauseelement(self, multiparams, params)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py",
> line 826, in _execute_clauseelement
> compiled_sql, distilled_params
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py",
> line 958, in _execute_context
> context)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py",
> line 1160, in _handle_dbapi_exception
> exc_info
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/util/compat.py",
> line 199, in raise_from_cause
> reraise(type(exception), exception, tb=exc_tb)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py",
> line 951, in _execute_context
> context)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/sqlalchemy/engine/default.py",
> line 436, in do_execute
> cursor.execute(statement, parameters)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/MySQLdb/cursors.py",
> line 205, in execute
> self.errorhandler(self, exc, value)
> File
> "/home/sys_user/Envs/flask/local/lib/python2.7/site-packages/MySQLdb/connections.py",
> line 36, in defaulterrorhandler
> raise errorclass, errorvalue
>
>
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