Why are there so many NoSQL databases?
pierrefar: Because they're all different. We have key-value stores (Berkley and MemcacheDB), column stores (Cassandra), document stores (CouchDB, MongoDB), and even new data structures (Redis).They all solve different types of problems (e.g. document stores vs key-value stores). Even similar databases solve the same problems differently (e.g. sharding). They have different performance profiles and bottlenecks. They give you different ways to model your data and query it. Some are persistent, some are not, and some are lazy persistent.Big picture though: this is the first time your average startup/small team/individual hacker has needed a very scalable database solution because of websites. A website has the ability to get you a ton of users very quickly even if you are just one man hacking on a personal pet peeve (I went through this).This kind of experimentation is awesome and it allows us to figure out what really works in what situations and is a sign of a very healthy community. I love being part of it.