Hive: Know SQL internals - how joins work, data structures and disk
algorithms, etc.. And how those would be implemented in MapReduce. Know
what a projection, aggregation, etc.. is.
Hadoop: Know how terasort works, know how word count works, and know about
why java serialization is non ideal. Know when the FileInputFormat and
Partitioner APIs would need to be used.
HBase: Understand the fundamental differences between HBAse and Cassandra,
how column scans are done, and how mapreduce is used against HBase