其實我們要的是內存數據庫引擎，就是暴露給我們的是JDBC的API，我們就像操作數據庫一樣的操作，但是數據并沒有寫入磁盤，而是在內存中。當然需要持久化時，你也可以把它寫入磁盤。
HSQLDB是這樣一個實現，它是一個數據庫引擎，可以作為嵌入式的數據庫，也可以作為內存數據庫。并且在很多知名的項目中已經有了應用比如openOffice。
我們應該關注一下！
http://hsqldb.sourceforge.net/

HSQLDB is the leading SQL relational database engine written in Java. It has a JDBC driver and supports a rich subset of ANSI-92 SQL (BNF tree format) plus SQL 99 and 2003 enhancements. It offers a small (less than 100k in one version), fast 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.

The product is currently being used as a database and persistence engine in many Open Source Software projects and even in commercial projects and products. In it's current version it is extremely stable and reliable. It is best known for its small size, ability to execute completely in memory and its speed.

This feature-packed software is completely free under our licenses , based on the standard BSD license. Yes, that's right, completely free of cost or onerous restrictions and fully compatible with all major open source licenses. Java source code and extensive documentation always included!

Users please visit the Project Summary Page for more information and to submit Patches, Bugs, Feature Requests and communicate with the Project Team or view/browse/subscribe to one or more of our mailing lists.

Also visit our pages featuring HSQLDB for the Sharp Zaurus platform, a special version with a data entry and view interface.

Developers please visit the Developers Page and join our effort!

Our group was formed in 2001 and has as its charter the continuation of Thomas Mueller's closed Hypersonic SQL Project. We have actively developed and released six new versions of the database since April 2001. The latest release version features a wide range of new functionality and code rewrite. The project enjoys an overall ranking of 82 among all SourceForege projects (85,000) with over 380,000 downloads.

The last stable code from Thomas' project (Hypersonic SQL version 1.43) is also available for download at Thomas Mueller's Hypersonic SQL page at SourceForge.