db4o 4.3 has been released as a "production" version today. This release includes all the changes in the development releases 4.1 and 4.2. The two most important new features stepping up from 4.0:
- Database file sizes of up to 254GB are possible
- Full support for all JDK 5 features is provided

New in 4.3:

• File IO is pluggable
  To create your own file IO implementation, you simply have to inherit from the abstract class com.db4o.io.IoAdapter and implement all the abstract methods. We have included two demo implementations with the download:
  - a JNI implementation for Windows in /src/com/db4o/util/io/win32/
  - an NIO implementation in /src/com/db4o/util/io/NIOFileAdapter
  However these implementations are just intended as technical demonstrations, they have not been validated in heavy productive use. Here are some possible usecases why you may consider to write your own IoAdapter implementation:
  - achieve maximum performance with a native library for your platform
  - encrypt and decrypt slots with any fixed-length encryption mechanism of your choice
  - improve your security against hardware failures with a read-after-write check
  - mirror file IO to a redundant secondary or backup system
  

Enjoy!