BlueDB is an on-disk, special-purpose datastore optimized for time-based data retrieval using small amounts of memory.
BlueDB is simple, light on memory usage, and most importantly: fast at reading a large number of objects for a specified time period. It is written in pure Java and intended to be embedded within a Java application. It does not support any kind of query language or API from another process.
It's written in pure Java and is single-user. Reads are eventually consistent. Writes are fully serializable.
BlueDB utilizes FST for ultra-fast object serialization/deserializaion and special file-system directory structures to build near constant-time access to records by ID or time.
For more information visit: bluedb.org