9d2f8043_Troubleshooting_Impala__Recommendation
[Symptom] Queries are slow to return results. [Explanation] Some impalad instances may not have started. Using a browser, connect to the host running the Impala state store. Connect using an address of the form http://hostname:port/metrics. Note: Replace hostname and port with the hostname and port of your Impala state store host machine and web server port. The default port is 25010. The number of impalad instances listed should match the expected number of impalad instances installed in the cluster. There should also be one impalad instance installed on each DataNode [Recommendation] 
Ensure Impala is installed on all DataNodes. Start any impalad instances that are not running.
Troubleshooting Impala