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Process implementation is the application logic to handle requests. For example, the ThriftCLIService.ExecuteStatement() method implements the logic to compile and execute a Hive query.

Dependencies of HS2

• Metastore
  The metastore can be configured as embedded (in the same process as HS2) or as a remote server (which is a Thrift-based service as well). HS2 talks to the metastore for the metadata required for query compilation.  

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HS2 clients: HiveServer2 Clients

User interface:  Web UI for HiveServer2

Metrics:  Hive Metrics

Cloudera blog on HS2: http://blog.cloudera.com/blog/2013/07/how-hiveserver2-brings-security-and-concurrency-to-apache-hive/