LINK

HyperDB is a very advanced database class that replaces a few of the WordPress built-in database functions. The main differences are: * HyperDB can be connect to an arbitrary number of database servers, * HyperDB inspects each query to determine the appropriate database. It supports: Read and write servers (replication) Configurable priority for reading and writing Local and remote datacenters Private and public networks Different tables on different databases/hosts Smart post-write master reads Failover for downed host Advanced statistics for profiling It is based on the code currently used in production on WordPress.com with many MySQL servers spanning multiple datacenters.