Oracle Berkeley DB is the industry-leading open source, embeddable storage engine that provides developers a fast, reliable, local database with zero administration. Oracle Berkeley DB is a library that links directly into your application. Your application makes simple function calls, rather than sending messages to a remote server, eliminating the performance penalty of client-server architectures.

via Oracle Berkeley DB.

We’ve combined the strengths of SQLite with the strengths of Berkeley DB. If you choose the SQL API then the Berkeley DB APIs are completely hidden, your program is written to use the SQLite APIs. Because this is a full SQL database engine you are free to use JDBC, ODBC or any other compatible access layer as well.

This DB is called db4.  I needed to yum install db4-devel to compile squidguard to use this database.