[GitHub] [airflow] potiuk edited a comment on pull request #21431: [scheduler HA]catch sqlalchemy leaking LockNotAvailable Exception during multiple scheduler instances comes up

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potiuk edited a comment on pull request #21431:
URL: https://github.com/apache/airflow/pull/21431#issuecomment-1034841394


   That could indeed explain it @uranusjr :
   
   It was this part of the code. It was raised in the `Pool.slots_stats(lock_rows=True` but it is just "after" the advisory lock execute that looks like might be the root cause (though - at least in theory) the lock SHOULD be acquired in this case. . 
   
   ```
           if session.get_bind().dialect.name == "postgresql":
               # Optimization: to avoid littering the DB errors of "ERROR: canceling statement due to lock
               # timeout", try to take out a transactional advisory lock (unlocks automatically on
               # COMMIT/ROLLBACK)
               lock_acquired = session.execute(
                   text("SELECT pg_try_advisory_xact_lock(:id)").bindparams(
                       id=DBLocks.SCHEDULER_CRITICAL_SECTION.value
                   )
               ).scalar()
               if not lock_acquired:
                   # Throw an error like the one that would happen with NOWAIT
                   raise OperationalError(
                       "Failed to acquire advisory lock", params=None, orig=RuntimeError('55P03')
                   )
   
           # Get the pool settings. We get a lock on the pool rows, treating this as a "critical section"
           # Throws an exception if lock cannot be obtained, rather than blocking
           pools = models.Pool.slots_stats(lock_rows=True, session=session)
   ```


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