hi,team:

    my dag is 1 minute schedule,one parts dag state is success,but tasks state is not yet started in a dag:

![image](https://user-images.githubusercontent.com/41068725/116344664-357d8780-a819-11eb-8010-c746ffdfdbcc.png)


   how can to fix it?
airflow/settings.py
"""Prepare SQLAlchemy engine args"""
    engine_args = {}
    pool_connections = conf.getboolean('core', 'SQL_ALCHEMY_POOL_ENABLED')
    if disable_connection_pool or not pool_connections:
        engine_args['poolclass'] = NullPool
        log.debug("settings.prepare_engine_args(): Using NullPool")
    elif not SQL_ALCHEMY_CONN.startswith('sqlite'):
        
        
        
        pool_size = conf.getint('core', 'SQL_ALCHEMY_POOL_SIZE', fallback=5)