sjyangkevin opened a new pull request, #64520:
URL: https://github.com/apache/airflow/pull/64520
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related: #64415
### Why
The sync `SessionDep` session is held open from the moment the endpoint
function starts until the `StreamingResponse` generator is fully consumed and
FastAPI cleans up the dependency. During the polling loop (while
`dag_run.state` not in `State.finished_dr_states: await
asyncio.sleep(self.interval)`), the sync DB connection sits idle but checked
out from the pool. If a DAG run takes minutes or hours to complete, that
connection is locked for the entire duration. With many concurrent `/wait`
requests, this can exhaust the connection pool.
This PR improves the above by opening a short-live session in
`_serialize_xcoms`, similar to what have been done in `_get_dag_run`.
https://github.com/apache/airflow/pull/64415#discussion_r3007522560
### Test Cases
Tests should have been handled in **test_collect_task** and
**test_should_respond_200_immediately_for_finished_run**
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