HiStore

The hierarchical store is the default store (and currently the only one implemented).

It stores files in a mechanism similar to Squid. (Or at least the way it used to -- I don't know anymore.), 256 per directory, 4 levels deep. This allows for 4 billion plus resources, plus infinite versions. You should never run out of IDs. (Of course if you do then you can use a 64 bit version, which holds ALOT more).

It chooses keys by a random (ie sequential) order and stores resources one per directory.

It uses a cache to map GUIDs and UUIDs to HiStore keys.