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[AIRFLOW-2511] Fix improper failed session commit handling #4769
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Does this change also mean we open and close a connection for each TI? Does that have any impact on performance?
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Good point.
Not necessarily so, it just means that each TI gets its own session, which may or may not mapped to new connection as SQLAlchemy/Airflow does connection pooling. In fact, we use ti.refresh_from_db() a lot, where a new session object is created per call (
airflow/airflow/models/__init__.py
Line 932 in c50a851
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In general I think we should let SQLAlchemy do the pooling and close the sessions that we don't use anymore, instead of keeping them open and passing them around all the time.
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Personally I would prefer to have a
create_session
, since we commit the result on the last line anyway. If we do this properly, we shouldn't have to dorefresh_from_db
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I think SQLAlchemy does the pooling but is un-opinionated about how sessions are managed. The following access pattern is recommended per https://docs.sqlalchemy.org/en/latest/orm/session_basics.html#when-do-i-construct-a-session-when-do-i-commit-it-and-when-do-i-close-it, which is what Airflow follows:
airflow/airflow/utils/db.py
Line 37 in c50a851
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Any other concerns? @Fokko @ashb
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Thanks for the reference link, no further concerns from my side.