Why is NHibernate.Cache.HashtableCacheProvider not intended for production use?

Question

The NHibernate documentation and the book NHibernate In Action state that the cache provider NHibernate.Cache.HashtableCacheProvider is not intended for production

Answer 1

Because it doesn't support any kind of reasonable caching semantics (first example that comes to mind: timeouts), and it basically grows indefinitely.

It's intended for testing only, as it just provides the simplest possible implementation of a local cache.