Why? His data set is larger than ram, and couchdb is a really great disk based key/value store.
Last time I checked CouchDB was a document store with MapReduce queries. A very different beast from Redis.
It's really a much longer story. We use Redis and Couch together. Redis for caching, Couch for long-term storage.
Whether Couch has or doesn't have Map/Reduce is irrelevant, really. Couch Map/Reduce is a toy (just like Riak) and is not to be trusted. We avoid it as much as possible.
> Couch Map/Reduce is a toy (just like Riak) and is not to be trusted.