Riak 0.14.0 included a couple of very exciting improvements for Map/Reduce. In a recent post, Basho guys are spending again some time to explain them:
If the application can store meaningful data in the keys, then key filtering can query just the keys and load only the objects whose keys pass the filter to be processed by the MapReduce job. […] Key filtering will support boolean operators (and, or, not), url decoding, string tokenizing, regular expressions, and various string to numeric conversions.
Original title and link: Riak Map/Reduce Improvements Explained (NoSQL databases © myNoSQL)