Data processing unit with key value store

A key-value store supporting GET, PUT and DELETE operations, serializes multiple clients using two locks, and that supports asynchronous resizing. The locking scheme includes an operation of holding two locks, one for the key involved in the operation, one for the page currently searched or updated. The store can either be a single volume holding keys and data or can be organized as a directory volume referencing a number of data volumes organized by data-size ranges. The scheme also supports asynchronous resizing of the directory while continuing to perform operations.