In my situation, I don't care about the performance at all, because I don't have many keys at any given moment. The few that I have matter greatly.
I care that when I store a key, it's reliably, durably, stored and replicated, and that when nodes fail I don't have to do anything special to keep running. (This is in contrast to PostgreSQL, MySQL, or Mongo replication, where you have to fail over, then switch back eventually, and it takes special effort.)
AFAICT, It's not provided by Redis or CouchDB either, because their replication is async -- keys can get lost.
Having looked at a bunch of options in the last couple weeks, it seems like only Riak and Cassandra truly offer durable, synced replication that isn't difficult to admin. (...and of the two of them, Riak's documentation gives much more confidence about the ongoing admin efforts.)
Has anyone used any solid options I've perhaps overlooked?
This is unlikely to be a problem in practice. But it is a possibility to be aware of.
[1] http://www.mongodb.org/display/DOCS/Why+Replica+Sets
[2] http://www.mongodb.org/display/DOCS/Verifying+Propagation+of...
[3] http://www.mongodb.org/display/DOCS/Journaling
[4] http://www.mongodb.org/display/DOCS/Replica+Sets+-+Priority
* If I want to ensure that my data is written to three machines, all my writes will stop working in MongoDB if one machine goes down. With Riak, it will start issuing the writes to another node in the cluster and rebalance when the missing node comes back online.
* If I'm running MongoDB in a sharded configuration, if one of the shards cannot be reached, all writes will stop. With Riak, any node will accept the writes and, once the network issues are resolved, move them to the appropriate node.
That said, conflict resolution is hard and there's no real way to get around it when you're using a distributed database like Riak. With Riak, as Chad says you get "increased development complexity for massively decreased deployment complexity." There's no silver bullet, it's important to look at the trade-offs of each option.
Some of the Riak documentation was incomplete/incorrect which made implementation a little sticky, but the mailing list is extremely responsive and helpful.
Otherwise, have had a great experience with Riak thus far. Looking forward to the ease of scaling as well!
My sources at Basho tell me that this is fixed in 1.0, but until that's officially released, basically don't try to list keys.
This means that if you have buckets A (1 million items) and B (5 items), sequentially scanning bucket B will take just as long as scanning bucket A -- because Riak has to scan through the entire store. In other words, it's not enough to say that one should avoid scanning a bucket because it's slow when you have lots of stuff in a bucket; it's always too slow to be practically usable in any situation where you have more than a few hundred keys.
I think calling buckets is a big mistake because they create the expectation that they really are separate things. "Namespace" or "keyspace" would have been more appropriate. (Can buckets have different replication semantics? If not, that's even worse.)
Cassandra is loosely based on the same tech as Riak, and supports sequential range queries very well, I hear.
The single missing 'feature' (design decision) that I can't live without, is that you can't efficiently do range queries/order-by on the key in riak today.
Hopefully this will get easier with secondary indexes / riak-search integration. Not clear yet.
They are coming, though. That's what I hear, at least.
If we are talking about performing a range operation on the primary key which returns the matching objects, then no, Riak doesn't currently offer that. However, given it's support for an ordered data store such as leveldb in 1.0 it should only be a matter of time before that is possible.
Just to try it out I already implemented this for fun on my fork.
https://github.com/rzezeski/riak_kv/tree/native-range
https://github.com/rzezeski/riak-erlang-client/tree/native-r...
[0] http://wiki.basho.com/Configuration-Files.html#app.config
