It uses more memory and result number of entries will be smaller. It is database engine, physical laws still applies.

I was more interested in knowing whether you have any real world examples of MapDB?

MapDB is still too fresh, so there is no documentation or examples yet. But some people are already using it, mostly for parsing large text files.

Previous versions were called JDBM and it has been around since 2001, so it has some solid user base. Problem is that nobody tells me until there is bug, which is not happening that often :-)

I'll say for JDBM3, the bugs must be few and far between; we haven't found any yet. Many thanks for a rock-solid library!