The developer of BangDB, Sachin Sinha, recently put a performance paper up on the High Scalability website
Berkeley DB is now owned by Oracle, but it’s been around for a long time. It’s a library that provides an embedded database for key/value data, written in C with bindings for a number of languages. Proprietary software requires a commercial license of around $900 to $14000 per processor.
LevelDB is a key-value library written by Google, somewhat faster in operation than Berkeley DB. It has built-in compression (using Snappy), is written in C, and is BSD licensed.
BangDB is a new entrant to the key-value database world, with embedded, network service, and distributed cluster modes. Only the embedded version has been released, and it’s BSD license. It’s written in C++.