Introduction to Hive metastore
Hive metastore (HMS) is a service that stores metadata related to Apache Hive and other services, in a backend RDBMS, such as MySQL or PostgreSQL. Impala, Spark, Hive, and other services share the metastore. The connections to and from HMS include HiveServer, Ranger, and the NameNode that represents HDFS.
HMS connects directly to Ranger and the NameNode (HDFS), and so does HiveServer, but this is not shown in the diagram for simplicity. One or more HMS instances on the backend can talk to other services, such as Ranger.