OpenLDAP's new MDB library is a highly optimized B+tree implementation that is orders of magnitude faster and more efficient than everything else in the software world. Reads scale perfectly linearly across arbitrarily many CPUs with no bottlenecks, and data is returned with zero memcpy's. Writes are on average twenty times faster than commonly available databases such as SQLite. The entire library compiles down to only 32K of object code, allowing it to execute completely inside a typical CPU's L1 cache. Backends for OpenLDAP slapd, Cyrus SASL, Heimdal, SQLite, and OpenDKIM have already been written, with other projects in progress.
The intended audience is developers writing system-level code, working in environments where absolute efficiency is required, such as mobile phones and other embedded devices, and high volume databases.