I'm not sure what switch you are referring to, they've been using HAProxy and Lucene for quite some time.
Also, what would a No SQL data store give them (for central data storage - not caching) that they aren't already handling with SQL? Keep in mind that they also have relatively easily partionable data (if necessary they can break off any StackExchange site and database to their own dedicated hardware).
Also, what would a No SQL data store give them (for central data storage - not caching) that they aren't already handling with SQL? Keep in mind that they also have relatively easily partionable data (if necessary they can break off any StackExchange site and database to their own dedicated hardware).