Build RAMDirectory on FSDirectory, and then synchronzing the two

[Cheng]

Hi,

I new a RAMDirectory based upon a FSDirectory. After a few modifications, I
would like to synchronize the two.

Some on the mailing list provided a solution that uses addIndex() function.

However, the FSDirectory simply combines with the RAMDirectory, and the
size doubled.

How can I do a real synchronization?

Thanks