Impala Daemon
Impala Daemon is a deamon process that runs on each DataNode of the cluster.It reads and writes to data files;You can submit a query to it and that instance of the daemon serves as the coordinator node.The other nodes transmit partial results back to the coordinator.
The Impala Statestore
It checks on the health of impala daemons on all the datanodes in a cluster，It represented by a daemon process named statestored;It make sure that you querys arrived correct datanode of cluster。It’ not critical to an Impala cluster。if statestore is not running，The Impala daemons running as well as usual。
THe impala Catalog Service
catalog Service relays the metadata changes from Impala SQL statements to all the Impala daemons.It’s represented by a daemon process named catalogs;