Would be great to have AR support for VoltDB DBMS.
They’ve released a native PHP driver and it’s a very promising DB which is a mix between NoSQL & relational SQL. The database retains the data in RAM or disk partitions and distributes both the data and the SQL engine which processes it, across the server or server cluster’s processor cores. VoltDB is designed to ensure transactional consistency while eliminating legacy overhead.
In short it’s designed for the Web and takes care of sharding while still using SQL as a query language.