I will be co-presenting a talk at the MySQL Conference on Thursday April 23 in Santa Clara, California on the back-ndb backend in OpenLDAP. Johan Andersson from Sun/MySQL will also be presenting; Symas and MySQL worked together to design the data model for this backend.
http://en.oreilly.com/mysql2009/public/schedule/detail/6219
back-ndb is a new OpenLDAP slapd backend that provides direct access to MySQL's NDB Cluster engine. The NDB Cluster design allows concurrent access to relational tables from multiple access methods (including mysqld for traditional SQL access, and slapd for LDAP access) and allows capacity to scale horizontally across multiple data nodes. The OpenLDAP backend uses the native NDBAPI to achieve high speed access without any SQL translation overhead. Multiple slapd servers can operate concurrently on an NDB database, along with other mysqld servers and other agents, allowing performance to be augmented linearly simply by adding more nodes to a cluster.
This will be slightly more in-depth than the back-ndb talk I presented at the UKUUG conference in March.