HSQLDB

HSQLDB (HyperSQL DataBase)

Screenshot  HSQL Database Manager
Stable release	1.8.0.10 / 2008-06-02; 12 months ago
Preview release	1.9.0 Beta 3 / 2009-06-10; 5 days ago
Written in	Java
Operating system	Cross-platform
Type	RDBMS
License	BSD license
Website	http://hsqldb.org

HSQLDB (Hyper Structured Query Language Database) is a relational database management system written in Java. HSQLDB is based on Dr. Mueller's discontinued Hypersonic SQL Project.^[1].

HSQLDB is available under a BSD license.

It has a JDBC driver and supports a large subset of SQL-92, SQL-99, and SQL:2003 standards.^[2] It offers a fast,^[3] small (less than 100 kilobytes in one version, around 600 kilobytes in the standard version) database engine which offers both in-memory and disk-based tables. Embedded and server modes are available.

Additionally, it includes tools such as a minimal web server, in-memory query and management tools (can be run as applets), and a number of demonstration examples. It can run on Java runtimes from version 1.1 upwards, including free Java runtimes such as Kaffe.

HSQLDB is currently being used as a database and persistence engine in many open source software projects, such as OpenOffice.org Base and the Standalone Roller Demo,^[4] as well as in commercial products, such as Mathematica or InstallAnywhere (starting with version 8.0).^{[citation needed]}

Over 250 book titles document the use of HSQLDB for application development with frameworks such as Spring Framework or Hibernate.^[5]

Transaction support

HSQLDB version 1.8.0 supports transaction isolation level 0 (read uncommitted) only. It means a SQL query in one session might occasionally fetch uncommitted data from another session.^[6] Version 1.9 (currently an alpha version) supports read committed and serializable isolation levels. According to the official web site news section, "a separate version with multiversion row concurrency control was successfully developed and has undergone internal tests. This will be released as version 2.0". There is no information on when it will be available.

Data storage

HSQLDB has two main table types used for durable read-write data storage (i.e. if transaction has been successfully committed, it is guaranteed that the data will survive system failure and will keep its integrity).

The default MEMORY type stores all data changes to the disk in the form of a SQL script. During engine start up, these commands are executed and data is reconstructed into the memory. While this behavior is not suitable for very large tables, it provides highly regarded performance benefits and is easy to debug.

Another table type is CACHED, which allows one to store gigabytes of data, at the cost of the slower performance. HSQLDB engine loads them only partially and synchronizes the data to the disk on transaction commits. However, the engine always loads all rows affected during an update into the memory. This renders very large updates impossible without splitting the work into smaller parts.^[7]

Other table types allow for read-write CSV-file access (these tables can participate, for example, in queries with JOINs and simplify spreadsheet processing) and read-write non-durable in-memory data storage.

See also

• List of relational database management systems
• Comparison of relational database management systems
• OpenOffice.org Base
• H2
• Apache Derby
• Change control

References

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External links

• HSQLDB at SourceForge.net
• Software using HSQLDB
• Books referring to HSQLDB (Google Books)