On Sep 18, 2010, at 6:52 PM, Randall Nortman wrote: > In testing my code for concurrency, I discovered that transactions are > not properly isolated on sqlite, even with > isolation_level='SERIALIZABLE'. It turns out that on the sqlite > dialect, do_begin() does nothing. As a result, transactions are not > isolated as expected. Dirty writes are easy to construct; using the > ORM: > > (assuming a mapped class Foo with attributes id and bar, and a Foo > with id=1 existing in the database) > > Process A: foo = Session.query(Foo).filter_by(id=1) > Process B: foo = Session.query(Foo).filter_by(id=1) > Process A: foo.bar = 'happy happy' > Process B: foo.bar = 'joy joy' > Process A: Session.commit() > Process B: Session.commit()
Oh and also, when you above say "Process A", "Process B", I assume those are separate processes. The default connection pool used with SQLite is the SingletonThreadPool - the same connection is used globally in a thread, so if your test above occurs within a single thread, you should select a different pool implementation. See: http://www.sqlalchemy.org/trac/wiki/FAQ#IamusingmultipleconnectionswithaSQLitedatabasetypicallytotesttransactionoperationandmytestprogramisnotworking Further rationale on this is available at : http://www.sqlalchemy.org/docs/dialects/sqlite.html?highlight=sqlite#threading-behavior -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@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.
