Riak has TTL with bitcask backend

[phated]

It seems you are implementing the getIndex against the leveldb backend. Is there a reason that bitcask isn't supported?

[nlf]

The expiry option for the bitcask backend is a global option, which is somewhat awkward to use and would require this module to completely ignore the ttl option passed in. We went this route to make sure that catbox's ttl option actually has meaning.

Providing an option to disable the gc function and not attempt to store indexes should be easy enough, but this is a tough problem to solve.