http://docs.oracle.com/cd/E17076_04/html/gsg/JAVA/BerkeleyDB-Core-JAVA-GSG.pdf
compare with sqlite
http://www.oracle.com/technetwork/database/berkeleydb/learnmore/bdbvssqlite-wp-186779.pdf
http://www.oracle.com/technetwork/products/berkeleydb/bdb-sqlite-comparison-wp-176431.pdf