What is Metadata DB Derby?

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I am new to Apache Hadoop. I came across something Derby. What is the meaning of Metadata DB Derby. I heard it is some file system. But can anybody tell what exactly is it & its working?

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brandon.bell On

Hadoop's Namenode stores metadata regarding where a file is stored on HDFS. That is, when you put a file onto HDFS, it gets replicated 3 times (by default) and the Namenode keeps track of which 3 servers are hosting the file.

Hive's Metadata is separate from the Namenode's metadata. Hive's Metadata maintains locations of it's underlying partitions, tables, databases, etc. The table schemas are also stored in Hive's Metadata. Hive requires a database backend to maintain this metadata, Derby is simply the default embedded metastore for Hive.

See http://hortonworks.com/blog/hdfs-metadata-directories-explained/ and https://cwiki.apache.org/confluence/display/Hive/AdminManual+MetastoreAdmin