Apache Sqoop(TM) is a tool designed for efficiently transferring bulk data between Apache Hadoop and structured datastores such as relational databases.
An explanation of Eric Brewer's CAP theorem, which says you cannot have more than two of Consistency, Availability and Partition-tolerance in web-based distributed systems.
J. Gray. Very Large Data Bases, 7th International Conference, September 9-11, 1981, Cannes, France, Proceedings, page 144-154. IEEE Computer Society, (1981)