I. Introduction
Recently, with the rapid development of the Internet, the growth rate of information is beyond our imagination. The traditional centralized database is inadequate to cope with the large scale SNS web and the e-Business web, such as Facebook, and Amazon. The vast amounts of data in web 2.0 have the following characteristics [2]:
Large volume of data, requires a lot of database to meet the efficient data storage.
High availability and scalability, traditional database is difficult to achieve the expansion by adding server nodes.
High concurrent of reading and writing.