But you have Nginx installed and running, and do not want to install Apache or Lighttpd instead - also you do not want to use legacy and slow CGI protocol (actually smokeping uses SpeedyCGI but it's also very old and legacy now )
Runs on MySQL (was 1800 servers and only 2 DBAs, now over 2500 servers) and DO NOT PLAN to move to anything! Cassandra was used only in inbox search, now replaced with HBase.
2. Twitter. Gave up migrating to Cassandra after a year of tryouts - " For now, we're not working on using Cassandra as a store for Tweets. This is a change in strategy. Instead we're going to continue to maintain our existing Mysql-based storage. "
" These distributed databases like Cassandra, MongoDB, and CouchDB aren't actually very scalable or stable. Twitter apparently has been trying to move from MySQL to Cassandra for over a year. When someone reports using one of these systems as their primary data store for over 1000 machines for over a year, I'll reconsider my opinion on this. "
Adam D. Angelo, former Facebook VP & CTO, founder of Quora.
Quora was founded in the end of 2010 and using MySQL as main storage.
So, there is (somewhat trolling and discussable) conclusion -
NoSQL solutions are good, but SQL is still proven and reliable data store for PRIMARY data source of project. NoSQL can be used for caching purposes or for some specific functions. Use primary NoSQL storage only for small or personal project, or if you are brave and/or have enough money to risk :)