Welcome to H2, the Java SQL database. 
The main features of H2 are:
- Very fast, open source, JDBC API
- Embedded and server modes; in-memory databases
- Browser based Console application
- Small footprint: around 1.5 MB jar file size
More information: http://h2database.com
Features
| H2 | Derby | HSQLDB | MySQL | PostgreSQL | |
|---|---|---|---|---|---|
| Pure Java | Yes | Yes | Yes | No | No |
| Memory Mode | Yes | Yes | Yes | No | No |
| Encrypted Database | Yes | Yes | Yes | No | No |
| ODBC Driver | Yes | No | No | Yes | Yes |
| Fulltext Search | Yes | No | No | Yes | Yes |
| Multi Version Concurrency | Yes | No | Yes | Yes | Yes |
| Footprint (jar/dll size) | bug MB | duplicate MB | bug MB | good first issue MB | invalid MB |