"SQL" is not a classification of a database, it's a query language. Some of the databases which use SQL do not scale well or easily, and some databases which d

"SQL" is not a classification of a database, it's a query language. Some of the databases which use SQL do not scale well or easily, and some databases which don't use SQL don't scale well either. What Adam means to say is "some of the semantics defined by SQL are hard to get correct while maintaining scalability." Hard is very different from impossible, and there is a large number of very smart people currently solving this problem very well. There is another large number of smart people trying to solve the problem by ignoring the hard parts of the semantics. It seems they will likely come up with something very fast and scalable, but ultimately less useful for certain things which are done easier with proper SQL semantics. In fact, it's not clear in all cases that they are even making something that's more performant: cf. http://sergeitsar.blogspot.com/2011/01/mongodb-vs-clustrix-comparison-part-1.html http://sergeitsar.blogspot.com/2011/01/mongodb-vs-clustrix-c... Saying "SQL Databases Don't Scale" is like saying "oil paintings on wood aren't appealing". Not all oil-on-wood paintings are good, but some are, and some tempera-on-fresco paintings suck too. The logic is simply invalid.