On Nov 14, 2012, at 2:38 PM, JonathanQ wrote:
> We have some code running against MySQL running in Amazon RDS. During an
> outage or the maintenance window - Amazon issues an automatic failover of our
> RDS instance. However our code doesn't failover with it.
>
> We are having issues with 2 of our applications (2 different issues):
>
> First one: Unable to rollback when we get the error "2006, 'MySQL server has
> gone away'"
>
> The issue we are having is that a DB operation will fail when the failover
> occurs. So in the event of an error we issue a rollback on the SqlSoup
> object (which delegates to the underlying session).
>
> sqlsoup_engine.rollback()
>
> However this rollback fails with the error:
>
> connection.rollback()
> OperationalError: (OperationalError) (2006, 'MySQL server has gone away')
> None None
>
> Subsequently our application continues on an then starts failing with:
> StatementError("Can't reconnect until invalid transaction is rolled back
> (original cause: InvalidRequestError: Can't reconnect until invalid
> transaction is rolled back)",)
OK well when you say "in the event of an error", is that an error that precedes
the rollback, and is it the same 2006 error ? or is the 2006 error new with
the rollback?
Basically, what should happen is, any DB operation, like execute, or commit,
rollback, can potentially throw a 2006. SQLAlchemy will detect this as a
"disconnect" situation, and discard all open connections that aren't checked
out. The next operation will use a brand new connection.
So without knowing if you're getting this same error multiple times or not,
you'd want to either rollback() a second time, or just throw away the Session
after the rollback() fails. With SQLSoup you'd want to get at it by
sqlsoup_engine.session.remove(), which will replace the current thread's
Session with a new one.
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