--- Edited after seeing the size of the file ---
50 to 60 GiB files! It seems that you would have to know that your DB engine didn't load all of that in memory at once, and was very efficient in handling / scavenging off-loaded data backing blocks.
I don't know if Cloudscape is up to the task, and I wouldn't be surprised if it wasn't.
--- original post follows ---
Cloudscape often fits the bill. It's a bit more than Berkeley DB, but it gained enough traction to be distributed even with some JDK offerings.
