9d2f8043_Troubleshooting_Impala__Recommendation
[Symptom] Queries are slow to return results. [Explanation] Impala may not be configured to use native checksumming. Native checksumming uses machine-specific instructions to compute checksums over HDFS data very quickly. Review Impala logs. If you find instances of "INFO util.NativeCodeLoader: Loaded the native-hadoop" messages, native checksumming is not enabled. [Recommendation] 
Ensure Impala is configured to use native checksumming as described in Post-Installation Configuration for Impala.
Troubleshooting Impala