How to best use connection pooling in SQLAlchemy for PgBouncer transaction-level pooling?

Question

Using SQLAlchemy to query a PostgreSQL database behind PgBouncer, using transaction-level pooling.

What is the best pattern to use for this kind of set up? Should I have one-engine-per-process, using a ConnectionPool, or should I create an engine per-request, and use NullPool for each one of them? Is there a different pattern altogether that I should be using?

Thanks very much! Let me know if more information is needed and I'll update ASAP.

Answer 1

with PGBouncer, you'd probably want to just stick with NullPool. In that case you may be able to share a single Engine across subprocesses since no socket connections will be carried over the subprocess boundary. But you can't share anything referring to a Connection object, like a Session with an active transaction, over this boundary. You definitely wouldn't want to do "engine-per-request" though, an Engine is an expensive object that accumulates a lot of information about a particular database URL the first time it sees it.