VoltDB

VoltDB is an in-memory database designed by Michael Stonebraker (who was involved in Ingres and POSTGRES), Sam Madden, and Daniel Abadi. It is an ACID-compliant RDBMS which uses a shared nothing architecture. It includes both enterprise and community editions. The community edition is licensed under the GNU Affero General Public License.

VoltDB is a scale-out NewSQL relational database that supports SQL access from within pre-compiled Java stored procedures. The unit of transaction is the stored procedure, which is Java interspersed with SQL. VoltDB relies on horizontal partitioning down to the individual hardware thread to scale, k-safety (synchronous replication) to provide high availability, and a combination of continuous snapshots and command logging for durability (crash recovery).

VoltDB uses a shared-nothing architecture to achieve database parallelism. Data and the processing associated with it are distributed among all the CPU cores within the servers composing a single VoltDB cluster. By extending its shared-nothing foundation to the per-core level, VoltDB scales with the increasing core-per-CPU counts on modern commodity servers.

By making stored procedures the unit of transaction and executing them at the partition containing the necessary data, it is possible to eliminate round trip messaging between SQL statements. Stored procedures are executed serially and to completion in a single thread without any locking or latching, similar to the LMAX architecture. Because data is in memory and local to the partition, a stored procedure can execute in microseconds. VoltDB's stored procedure initiation scheme allows all nodes to initiate stored procedures while ensuring that there is a single serializable global order.