[GitHub] [airflow] feng-tao commented on a change in pull request #5210: [AIRFLOW-4419] Restore used_slots and queued_slots Pool methods

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feng-tao commented on a change in pull request #5210: [AIRFLOW-4419] Restore used_slots and queued_slots Pool methods
URL: https://github.com/apache/airflow/pull/5210#discussion_r279868168
 
 

 ##########
 File path: airflow/models/pool.py
 ##########
 @@ -64,6 +95,8 @@ def open_slots(self, session):
         from airflow.models.taskinstance import \
             TaskInstance as TI  # Avoid circular import
 
+        # Issue a single query instead of using the used_slots/queued_slots to
+        # avoid load on DB
         used_slots = session.query(func.count()).filter(TI.pool == self.pool).filter(
             TI.state.in_([State.RUNNING, State.QUEUED])).scalar()
         return self.slots - used_slots
 
 Review comment:
   used_slot already include both tasks in running state and queued state. So no need to minus the queued slots.

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