HSQLDB (''Hyper SQL Database'') is a

relational database management system A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...

written in Java. It has a JDBC driver and supports a large subset of SQL-92, SQL:2008, SQL:2011, and SQL:2016 standards. It offers a fast, small (around 1300 kilobytes in version 2.2) database engine which offers both

in-memory An in-memory database (IMDB, or main memory database system (MMDB) or memory resident database) is a database management system that primarily relies on main memory for computer data storage. It is contrasted with database management systems that e ...

and disk-based tables. Both embedded and server modes are available. Additionally, it includes tools such as a minimal

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, command line and GUI 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 implementations such as

Kaffe Kaffe is a discontinued "clean room design" (reverse engineering) version of a Java Virtual Machine. It comes with a subset of the Java Platform, Standard Edition (Java SE), Java API, and tools needed to provide a Java runtime environment. Like m ...

. HSQLDB is available under a BSD license. It is used as a database and persistence engine in many

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software projects, such as descendants of

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(i.e.,

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, LibreOffice Base, etc.), and the

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VoIP and video-conference client since version 2.6. It is also used in commercial products, such as

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and InstallAnywhere (starting with version 8.0).

Transaction support

HSQLDB version 2.0 has three transaction control modes. It supports with table level locks or with multiversion concurrency control (MVCC), or a combination of locks and MVCC. version 1.8.1 supports

transaction isolation In database systems, isolation determines how transaction integrity is visible to other users and systems. A lower isolation level increases the ability of many users to access the same data at the same time, but increases the number of concurre ...

level 0 (read uncommitted) only.

Data storage

HSQLDB has two main table types used for durable read-write data storage, i.e., if a transaction has been successfully committed, it is guaranteed that the data will survive system failure and will keep their 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 are reconstructed into the memory. Another table type is CACHED, which allows one to store more data, at the cost of the slower performance. The 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. Other table types allow access to comma-separated values (CSV) files. These tables can participate, for example, in queries with JOINs and simplify spreadsheet processing and read-write non-durable in-memory data storage.

SQL features

HSQLDB 2.0 supports all the core features and many optional features of SQL:2008. Advanced features include user-defined SQL procedures and functions, schemas, datetime intervals, updatable views, arrays, lobs, full and lateral joins and set operations. Many non-standard functions such as TO_CHAR and DECODE are also supported. Extensions to standard SQL include user-defined aggregate functions.

Releases

Several versions of HSQLDB have been released since 2001. Early versions were based on the discontinued HypersonicSQL database engine. Version 2.0, released in 2010, is mostly new code, written to conform to Standard SQL and JDBC 4 Specification. Version 2.3.2 (released in 2014) is fully multi-threaded and supports high performance

two-phase locking In databases and transaction processing, two-phase locking (2PL) is a concurrency control method that guarantees serializability.Phil Bernstein, Philip A. Bernstein, Vassos Hadzilacos, Nathan Goodman (1987) ''Concurrency Control and Recovery in Dat ...

and MVCC (multiversion concurrency control) transaction control models.

References

External links