H2 Database on GAE

H2-GAE is an experimental port of the H2 Database Engine to Google App Engine (GAE) using GaeVFS. H2-GAE is currently not suitable for production use.

As of July 21, 2009 the current status is:

• Basic operations such as CREATE TABLE, DROP TABLE, INSERT, and SELECT are working.
• INSERT is very, very slow.
• SELECT seems to perform reasonably well.
• There is currently no distributed locking mechanism that works across multiple GAE application instances running in separate JVMs. This could result in corruption of database files.

Download and Installation

H2-GAE requires GaeVFS 0.3 and its dependencies. Copy h2-gae-EXPERIMENTAL.jar, gaevfs-0.3.jar, commons-vfs-2.0-SNAPSHOT.jar, and the required dependencies into your project's WEB-INF/lib directory. H2-GAE only works in Embedded Mode as described in the H2 tutorial.

JDBC Driver Class

The JDBC Driver Class for H2-GAE is: org.h2.Driver

JDBC URLs

JDBC URLs for H2-GAE take the following format:

jdbc:h2:gae://<partial-path>;FILE_LOCK=NO;AUTO_SERVER=FALSE;DB_CLOSE_ON_EXIT=FALSE

Where <partial-path> is a partial GaeVFS path specification. The path is "partial" because it does not specify a complete file name, but instead specifies a database name that is used by H2 to generate file names. For example, the following JDBC URL specifies a database named test:

jdbc:h2:gae://test;FILE_LOCK=NO;AUTO_SERVER=FALSE;DB_CLOSE_ON_EXIT=FALSE

When processing this URL, H2-GAE creates the following files--among others--within the webapp root (virtual) directory:

test.data.db
test.index.db
test.trace.db

The JDBC URL can specify directories within the partial path, for example:

jdbc:h2:gae://WEB-INF/data/test;FILE_LOCK=NO;AUTO_SERVER=FALSE;DB_CLOSE_ON_EXIT=FALSE

The above JDBC URL will result in the following files (among others):

WEB-INF/data/test.data.db
WEB-INF/data/test.index.db
WEB-INF/data/test.trace.db

The GaeVfsServlet can be used to download these files.

Specifying the FILE_LOCK=NO, AUTO_SERVER=FALSE and DB_CLOSE_ON_EXIT=FALSE parameters is required; if omitted or set to different values, H2-GAE will throw exceptions and fail to startup.

Source Code

Source code patches to the H2 Database Engine and Apache Commons VFS required to support H2-GAE are available within the SVN repository on this web site.