Comparison to shared memory or mmap'd files -- by using files we let the filesystem manage the cache, so we don't have to be concerned with the data growing and causing memory pressure. We also don't have to worry about how to store the data in a format friendly to fast retrieval, since this is provided by sparkey.

Comparison to local dbs like cdb, sparkey, mapdb, gettext files etc. -- hammerspace is a gem that uses sparkey under the hood, so these solutions are more or less one and the same. The difference is that hammerspace exposes a ruby hash-like API to make integration with existing applications easier. It also provides concurrent writer support, which many local dbs don't do.

Whether it's a good idea or not is for you to judge -- we've open sourced the gem in hopes that it will be useful to someone, just as sparkey and gnista were useful to us.