The SQL architecture is a distributed relational database. There are several excellent implementations of this architecture, that are designed to support extremely large databases.
They offer a good compromise between the distributedness, and the
In particular the database can be replicated in order to improve
scalability and fault tolerance, as long as the number of
queries operations dominates the number of
The R-GMA architecture is being developed to address this problem: the scalability of the architecture is further improved introducing components that combine data from the database and cache the results (similar to NWS forecasters).