The metastore is a database for system-related metadata. It stores details about the tables, partitions, schemas, column types, and table locations. It can be accessed via the Thrift interface, making it possible to read this data using clients written in many different programming languages. The data is stored in a relational database system and uses an Object-relational mapping (ORM) layer to read and write data into the store. The choice of using an RDBMS for the metastore was made to reduce the latency when serving this information to the Hive query compiler.

The ORM layer of the metastore allows a pluggable model where any RDBMS can be plugged into Hive. The default RDBMS used is Apache Derby, an open source relational data store. In practice, organizations use MySQL and other popular RDBMS suites to host the metastore. The data in the metastore imposes...