Skwish is a fast, simple, lightweight Java library for storing blobs on the file system. It allows multiple concurrent readers and writers, provides all-or-nothing write semantics, and is designed to survive abnormal, unclean shutdown. Skwish is a structured implementation of storing all blobs in a single file to save on file system I/O. Skwish is premised on the proposition that blob storage ought to be orthogonal to the task of indexing. It is meant to be a clean and simple store on which some other index can be built.
io-util is a small, scalable Java library for slicing and dicing fixed width tables on disk. The objective is to provide reusable blocks of code for building efficient, custom binary data stores. It allows you to build, search, and maintain a large, externally stored, fixed width, sorted table. The library user specifies the row width (in bytes), a row comparison function (which implicitly defines any given row's key), and an optional delete codec.