CODEWITHSUNDEEP
pythonsessionormsqlalchemyconnection-pooling
ethanH
ethanH

Reputation: 43

SQLAlchemy, how to use an ORM and Sessions with Connection Pooling?

I am working on a Pyramid application that uses SQLAlchemy's ORM library and thus we use sessions. I am not clear on how sessions and connection pooling work together or if I even need connection pooling when using sessions.

Currently, here is how we create a session:

engine = create_engine(connection_string)
Session = sessionmaker(bind=engine)

I have modified creating the engine to add connection pooling:

pooled_engine = create_engine(connection_string, pool_size=20, max_overflow=5,echo=True, echo_pool=True)
Session = sessionmaker(bind=pooled_engine)

This seems to work (the app connects to the db and can read/write to the db), but I can't tell if connection pooling is being used or not. I tried logging the connection pooling code, but I don't see anything on the console. I do however see SQL statements which is due to the echo flag being set to True.

I am not understanding how sessions and connection pooling work together or why I am not seeing log statements when echo_pool is set to True.

Any help would be appreciated,

Thank-you

Upvotes: 4

Views: 1432

Answers (1)

CleverLikeAnOx
CleverLikeAnOx

Reputation: 1496

The engine handles the connection pooling and it is enabled by default.

From the documentation:

The Engine returned by the create_engine() function in most cases has a QueuePool integrated, pre-configured with reasonable pooling defaults. If you’re reading this section only to learn how to enable pooling - congratulations! You’re already done.

I believe the Session objects do not correspond to database sessions. Rather they are ORM sessions. They do not actually even have a connection to the database unless they are querying or saving to the database. Note, I am not 100% sure on this, so if someone more knowledgeable about SQLAlchemy internals could confirm or edit this, that would be appreciated.

Upvotes: 2

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