HerdDB is a distributed Database, data is distributed among a cluster of server without the need of a shared storage.

HerdDB primary language is SQL and clients are encouraged to use both the JDBC Driver API and the low level API.

HerdDB is embeddable in any Java Virtual Machine, each node will access without network to local data.

HerdDB replication functions are built upon Apache ZooKeeper and Apache BookKeeper projects.

HerdDB is very similar to a NoSQL databases, in fact at the Low level is it basically a key-value DB with an SQL abstraction layer which enables every user to leverage existing known-how and to port existing applications to HerdDB.

HerdDB has been designed for fast "writes" and for primary key read/update data access patterns.

HerdDB supports transactions and "committed read" isolation level

HerdDB uses Apache Calcite as SQL parser and SQL Planner

Data, as in any SQL database, is organized in tables and, in order to leverage HerdDB replication function, tables are grouped inside Tablespaces.

A Tablespace is a logical set of tables that is the fundamental architectural brick upon which the replication is built.

There are some DB features which are available only among tables of the same tablespace:

• transactions may span only tables of the same tablespace
• subqueries may span only tables of the same tablespace

Replication is configured at tablespace level, so for each tablespace only one server is designed to be the 'leader' (manager) and then you may configure a set of 'replicas'. The system automatically replicates data between replicas and handles transparently server failures.

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HerdDB is under Apache 2 license.