Riak link-walking like a join?

Question

I am looking to store pictures in a NoSQL database (<5MB) and link them to articles in a different bucket. What kind of speed does Riak's link walking feature offer? Is it like a RDBMS join at all?

Answer 1

Links are not at all similar to JOINs (which involve a Cartesian product), but they can be used for similar purposes in some senses. They are very similar to links in an HTML document.

With link-walking you either start with a single key, or you create a map-reduce job that starts with multiple keys. (Link-walking/traversal is actually a special case of map-reduce.) Those values are fetched, their links filtered against your specification (bucket, tag) and then the matched links are passed along to the next phase (or back to the client). Of course, all of this is done in parallel (unlike a JOIN) with high data-locality.

Also, map-reduce isn't slow by itself, you just don't have a sophisticated query planner to do the hard work for you; you have to think about how you will query and organize your data around that as necessary.