我有一个由3个节点组成的ccm集群。我正在通过python脚本向它写入和读取数据。我可以很容易地写所有的数据（小的或大的）。当我从python脚本读取大量数据时，节点会被关闭。当尝试从cqlsh我可以读取任何数量的数据成功。我包括下面的错误信息。

temp = session.execute("""SELECT * FROM***.***""")

Traceback (most recent call last):
File "/home/divyansh/.local/lib/python3.6/site-packages/IPython/core/interactiveshell.py", line 3296, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "<ipython-input-2-fccba5094f88>", line 2, in <module>
SELECT * FROM***.***""")
File "cassandra/cluster.py", line 2240, in 
cassandra.cluster.Session.execute
File "cassandra/cluster.py", line 4198, in 
cassandra.cluster.ResponseFuture.result
cassandra.cluster.NoHostAvailable: ('Unable to complete the 
operation against any hosts', {<Host: 127.0.0.1:9042 datacenter1>: 
ConnectionShutdown('Connection to 127.0.0.1:9042 was closed',)})