VoltDB is a commercial in-memory DBMS that is scalable and ACID-compliant. VoltDB is designed to be a NewSQL relational database to work with mainly OLTP queries. It is designed to be a distributed database with sharding and data replication. It has both a commercial version and an open-source community version.


VoltDB originated from H-Store, a research project from Brown U and MIT under Michael Stonebraker, Samuel Madden, Andy Pavlo, etc. In 2009, it started as a spinoff in Boston, MA.


Non-Blocking Blocking

The snapshot creation could either block all the other transactions or be done in a non-blocking way (e.g. Copy-On-Write).

Concurrency Control

Deterministic Concurrency Control

VoltDB schedules transactions deterministically on each partition of the data in the cluster. For transactions that span across partitions, a global serial order controller is responsible for determining the execution order. MVCC mode is only used when taking snapshots.

Data Model


VoltDB is based on the standard relational model.


B+Tree Hash Table

Apart from the default tree index, VoltDB also supports hash index.

Isolation Levels


VoltDB supports serializable isolation level with ACID guarantee. The deterministic ordering of transactions is achieved by controllers at each data partition.


Command Logging

VoltDB supports transaction-level logging for all the stored procedures that are invoked. By command logging, the amount of memory overhead is minimized since a single stored procedure invocation could contain arbitrary number of SQL statements. Only logs after the latest snapshot are kept, and the logs are flushed to the disk at a regular interval. This feature is only available in the enterprise edition.

Query Execution

Materialized Model

Query Interface

SQL Stored Procedures

Apart from supporting most of the standard SQL statements, VoltDB also allows the user to define pre-compiled stored procedures.

Storage Architecture


VoltDB is designed to be an in-memory relational DBMS. Its data persistence is achieved by snapshots stored on disk.

Storage Model

N-ary Storage Model (Row/Record)

VoltDB is only designed for fast OLTP queries.

Stored Procedures


The stored procedure in VoltDB allows the user to define a transaction once and to be invoked later with given parameters. Stored procedures are pre-compiled to reduce execution time. Temporary queries are automatically comipled and executed as a stored procedure. VoltDB supports stored procedures written in SQL or Java.

System Architecture


VoltDB runs on a sharded DBMS cluster. Data partitioning and replication is done automatically across the cluster


Materialized Views

Views in VoltDB are materialized to improve read speed, and all updates to the original table will have a performance impact.

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