In 3C3D, after shutting down each DataNode then restarting it one by one and , the SessionPool is unable to connect to the cluster.

Deploy an IoTDB cluster using 3C3D and connect to the cluster for writing and querying via SessionPool. To simulate the process of cluster upgrading or parameter modification, shut down one DataNode at a time and then restart it. Perform this operation sequentially for all three DataNodes, ensuring that two DataNodes are always alive. After all three DataNodes have been restarted, the write and query programs will report errors, indicating that they cannot connect to the cluster.

In the attachment, org.example.realTimeQuery.RealTimeQueryV6 tests writing, and org.example.realTimeQuery.RealTimeQueryByQuery tests querying.