On Nov 1, 2011, at 5:49 PM, Benjamin Sims wrote: > Thanks for this. As an update, I put in code that notifies me when an error > occurs. The real cause of this seems to still be the 'MySQL has gone away' > error. This occurs in various places, always as the first DB call in a > request (obviously). > > Is my understanding correct that in order to solve this I have to make sure > that all DB calls do a session.close() or session.rollback() when finished?
If you're doing a web app with pyramid, there really should be built in, or very easy to implement, a single event at the end of the request - it calls session.close(), and that's it. You shouldn't have to do defensive rollback()/close() calls anywhere else, it should be automatic, ultimately occurring on just one line of code, somewhere. My understanding was that the whole zope sqlalchemy thing would at least do this, and the folks on the Pyramid list should be able to show you how. If some other part of your app is not within the usual "web request" system, such as a script that runs in the background, you'd need to ensure that system cleans up after itself too, but always, there should be an architecture in place that takes care of this, without the need for you to "remember to do it everywhere" - that's not how things like this should be done. A "MySQL has gone away" error can be a symptom of out-of-sequence calls on the connection, which would occur with concurrent access among multiple threads. You should make sure that no SQLAlchemy mapped object that you got from a Session is shared among threads, or pulled from a dictionary that threads share, or part of any kind of global registry, without special handling to ensure that individual threads get a local copy of the state before manipulating or reading from it. This refers to instances of objects, not the classes or mappings themselves which aren't subject to these limitations. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
