@Override
    protected Hive initialValue() {
      return null;
    }
This class has functions that implement meta data/DDL operations using calls
to the metastore.
It has a metastore client instance it uses to communicate with the metastore.

It is a thread local variable, and the instances is accessed using static
get methods in this class.
ql/src/java/org/apache/hadoop/hive/ql/metadata/Hive.java