This is a Lucene directory that will store an index in a Mongo database using Mongo's GridFS.
It's a simple port of Lucene's
FSDirectory, so it's doing things in the exact same way.
Two lock factories are provided:
MongoDocumentLockFactory: this factory uses a dedicated collection in the database to store locks as documents. It's the default lock factory.
MongoFSLockFactory: this factory uses files in GridFS to handle locks, just like the old