On Jun 17, 2008, at 10:09 AM, Laurence Rowe wrote:


I'm not sure connection pooling is really useful in a threaded environment with recycled sessions. You want n threads = n connections. If we started creating new sessions each request then things would be different.


For this to be efficient in SQLA (if there were no pool), you'd need to bind each Session to a Connection individually. If you create_engine() using a pool like NullPool then you'd get an unpooled engine that creates new connections on each checkout. In theory this would be fine, although we don't have any current test coverage for the "auto-reconnect" logic using NullPool with persistently- checked-out Connections so we'd have to build that up and ensure its working.

But if you are binding Sessions directly to Connections, theres still not really any disadvantage to the usual QueuePool implementation remaining in place. If you set it with max_overflow=-1 it will just hand out any number of connections.

I still prefer the Session bound to Engine approach, whereby each transaction uses a pooled connection, and returns the connection on rollback/commit. That way you don't need to worry about stale connections hanging around for sessions/threads that fall out of use.
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