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Comment by socratic | Hacker News Reader

I am increasingly interested in Riak, in part because a very vocal minority on HN seems to think it is the One True NoSQL solution.

However, I still don't quite get it. What is Riak? It seems to be some sort of Dynamo implementation (like the ironically ill fated Cassandra), but apparently it has a workflow engine? What do people use it for? What is it best at?

Right now we're using PostgreSQL, Redis, and S3. PostgreSQL gives us ACID, Redis gives us fast in-memory access, and S3 gives us an infinite KV store. Is there some reason to use Riak? Would Riak just replace S3?

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Ultimately it is a eventually consistent key-value store. They have map-reduce and a new meta-data thing that lets you query documents, but you really only want to use it if your data maps well to key/value (and lots of data does!). The really cool things are that it is truly horizontal scale - a new node brings read+write+map-reduce power, and that it will help you sleep better with its dynamo-ism.

If your values are very small Riak is probably a good replacement for S3. If your values are large then S3 is probably better than Riak.

I'm not so certain. A value written to riak has something on the order of 450bytes of overhead (as of version 0.14, not entirely certain of the exact overhead in 1.0). Basically riak will write your value to disk with a bunch of other data that it uses internally to do its thing. Writing a stream of integers, one integer per riak key, would be a bad idea (tm), imho.

Why do you say that Cassandra is ill-fated?

NoSQL seems to me to be a scene as much driven by hype as logic. (For better or worse, practitioners using and programming NoSQL systems tend to have little understanding of the 30+ years of relevant RDBMS academic literature, and 20+ years of distributed RDBMS academic literature.)

Given that, NoSQL adoption often appears driven by success stories. But Cassandra seems to have the opposite: numerous failure stories. Facebook, Digg, Reddit and a number of others have all tried Cassandra in production, and have either had serious complaints or moved off to either SQL or other solutions like HBase.

Of course, these failure stories are anecdotes, and numerous unrelated factors (like bad interactions between Cassandra and Amazon's EC2) could be at fault. But I'm not sure it matters.

Has anyone on HN had a really good experience with Cassandra? (This may be the wrong thread to ask for obvious reasons.)

Riak users have had quite the opposite results based on talks given at conferences and videos put online. Yammer, Voxer, Formspring, Bump are all riak customers and all have a video out there somewhere talking about how much the like riak. Yes riak and cassandra share a little bit of technology (being dynamo inspired), but most of cassandra woes seem to come from operational difficulties and not the technology theory. Riak has more of a focus on operational friendliness out of the box.

There are videos and talks out there from several customers listed on Basho's site, just take a look.

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