AttributeError: 'Connection' object has no attribute '_Connection__connection' when mysql server is restarted & Session.close() is performed

[Former user]

Python 2.7.2 Sqlalchemy 0.7.3

When I start my app, then restart mysql server, I receive this upon Session.commit() (same for Session.rollback(), Session.close() when catching SQLAlchemyError)

Most of the traceback is here:

    self = <sqlalchemy.orm.session.Session object at 0x2436a10>
     644
---> 645 self.transaction.commit()
     646
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/orm/session.py", line 313, in SessionTransaction.commit
    self = <sqlalchemy.orm.session.SessionTransaction object at 0x2436b50>
     312 if not self._prepared:
---> 313     self._prepare_impl()
     314
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/orm/session.py", line 304, in SessionTransaction._prepare_impl
    self = <sqlalchemy.orm.session.SessionTransaction object at 0x2436b50>
     303 except:
---> 304     self.rollback()
             stx = <ref offset=-1 name=self>
             t = (
                 <sqlalchemy.engine.base.Connection object at 0x23543d0>,
                 <sqlalchemy.engine.base.TwoPhaseTransaction object at 0x2354c10>,
                 True,
                 )
     305     raise
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/orm/session.py", line 338, in SessionTransaction.rollback
    self = <sqlalchemy.orm.session.SessionTransaction object at 0x2436b50>
    _capture_exception = False
     337 if transaction._parent is None or transaction.nested:
---> 338     transaction._rollback_impl()
             stx = <ref offset=-2 name=self>
             transaction = <ref offset=-2 name=self>
     339     transaction._deactivate()
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/orm/session.py", line 356, in SessionTransaction._rollback_impl
    self = <sqlalchemy.orm.session.SessionTransaction object at 0x2436b50>
     355 for t in set(self._connections.values()):
---> 356     t[1](1).rollback()
             t = <ref offset=-2>
     357
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 1960, in Transaction.rollback
    self = <sqlalchemy.engine.base.TwoPhaseTransaction object at 0x2354c10>
    1959     return
--> 1960 self._do_rollback()
    1961 self.is_active = False
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 2056, in TwoPhaseTransaction._do_rollback
    self = <sqlalchemy.engine.base.TwoPhaseTransaction object at 0x2354c10>
    2055 def _do_rollback(self):
--> 2056     self.connection._rollback_twophase_impl(self.xid, self._is_prepared)
    2057
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 1279, in Connection._rollback_twophase_impl
    self = <sqlalchemy.engine.base.Connection object at 0x23543d0>
    xid = '_sa_3756cd31c58d286a70a2b4e149749534'
    is_prepared = False
    1278
--> 1279 if self._connection_is_valid:
    1280     assert isinstance(self.__transaction, TwoPhaseTransaction)
  File "pyenv/lib/python2.7/site-packages/SQLAlchemy-0.7.3-py2.7-linux-x86_64.egg/sqlalchemy/engine/base.py", line 1031, in Connection._connection_is_valid
    self = <sqlalchemy.engine.base.Connection object at 0x23543d0>
    1030
--> 1031 return getattr(self.__connection, 'is_valid', False)
    1032
AttributeError: 'Connection' object has no attribute '_Connection__connection'

[Mike Bayer]

This is definitely a bug, though if I were developing this today the solution would be that you'd just get a much nicer exception about calling methods on an invalidated connection. However, the default transaction is apparently letting rollback/commit/whatever silently pass on an invalid connection, so for now that should be the behavior of the two phase transaction as well.

I'd skip the usage of "twophase=True" for now unless you are actually using it (very rare overall, triply so for MySQL).

tests: rollback(), commit(), invalidate(), close() on all three transaction types, for invalid connection, closed connection.

[Former user]

Well, removing twophase=True resolves the problem. The setting was left over from times when we used more than one db.

I also applied 2317.patch and tested with twophase=True and this patch seems to solve this issue.

Thanks

[Mike Bayer]

thanks ! I need to implement tests on the SQLAlchemy side, then I can commit this.

[Mike Bayer]

632043bc8a72651f497396eb17e6f2b19bf98608

[Mike Bayer]

backported to 0.6 in a6535d17fb41ec5c6bfed07687d9c1e05ff5e91e

[Mike Bayer]

Removing milestone: 0.7.4 (automated comment)