I do not see Riak or Cassandra as competing at all. In fact I would expect most applications that use Riak or Cassandra are also using a general-purpose database as well (such as MySQL or Mongo). You could use some of those databases as a general purpose database but it would be more work for little benefit. It makes more sense to me to use Riak or Cassandra for use-cases that really need high-throughput and unlimited write-scalability and use an app database for things like user accounts and preference management and all the little things that can take up a lot of development time but will never have really demanding runtime requirements (for 99.99% of internet apps).
There are a large number of well-established and quality installations of MongoDB. It works really well at both small and large scale and with a bit of tweaking (like any technology), can perform nicely.
There are certainly reasons for using Riak, HBase, Cassandra, etc. and there are reasons for using MongoDB. It is when people seem to act confused when their hammer isn't acting like a screwdriver that we get these blog posts.
Range sharding (for saas,shard by client_id).
No sorting by value on couchbase indexes? And many other small features.
On the other hand i love about couchbase: no mongos,all servers equal.
I'm curious on the index sorting though, do you mean in terms of specifying what to sort on, or that you can't sort at all? As far as I understood the new indexing capabilities allow at the very least to sort on numeric values and similar.
Also, we DO implement a two DB setup... Couchbase and MySQL. They both have their place.
> I wrote about what I was thinking at the time here