xBis7 opened a new pull request, #75974:
URL: https://github.com/apache/airflow/pull/75974
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This is a follow-up to https://github.com/apache/airflow/pull/71737 which
has been merged.
## Possible scenario
A Dag Run is active and while it's still running, the user deletes from the
Dag file, a task that has already finished.
On the next iteration of the scheduler's loop, it picks up that a finished
task doesn't exist anymore and marks its state as REMOVED in the database.
The object is already loaded in the session with the old state. The bulk
UPDATE in `_build_finished_tis` has
`.execution_options(synchronize_session=False)` which leaves the session's
stale memory copy intact and doesn't update it along with the DB.
The existing unit test was running `session.expire_all` right before the
check which was forcing the test's code to re-fetch from the DB and not read
the stale copy and that's why this inconsistency went unnoticed.
Currently nothing reads the stale copy inside the scheduler but one case
where this is an issue today, is when using the Listener API and the Dag Run
success hook reads the task instances. In that case, the hook will run between
the UPDATE and the commit and it will get the stale copy.
## Solution
Removing the option restores SQLAlchemy's default synchronisation which
updates the session's memory copy along with the DB.
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Claude code Fable 5.1 for research
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