Dennis Forbes has a ☞ great post about RDBMS scalability and the hype around NoSQL that ends up with something like “SQL is scalable and NoSQL isn’t for everyone”. I have posted a long comment to the original post, reproduced below for reference, and suggested a slight modification to that conclusion: SQL is scalable. SQL scalability isn’t for everyone. NoSQL isn’t for everyone either (nb SQL should be read in the context of the post as RDBMS.)
Below is my original comment:
The part I agree most is: “In the case of the NoSQL hype, it isn’t generally the inventors over-stating its relevance — most of them are quite brilliant, pragmatic devs — but instead it is loads and loads of terrible-at-SQL developers who hope this movement invalidates their weakness.”
Over MyNoSQL (a blog focused on NoSQL technologies), most of the people talking about real life uses of NoSQL mention the operational costs of RDBMS scaling (f.e. Twitter usage of Cassandra), a point that your post seem to agree upon too. Personally, I tend to believe that NoSQL as RDBMS are just tools for our job and there is nothing about the death of one of the other. But as we’ve learned over years, every new programming language is the death of all its precursors, every new programming paradigm is the death of everything that existed before and so on. The part that some seem to be missing or ignoring deliberately is that in most of these cases this death have never really happened. And I think the same will apply to NoSQL and RDBMS and OODB and etc.
As a side note, I’d say that the definition you are using for scalability, while not incorrect, is a bit too wide. I think Wikipedia definition is giving a more clearly delimitated definition. I have also found Jonathan Ellis presentation on scalability quite useful and easy to grok for everyone.
Last, but not least, while I do like your ending note: “SQL is Scalable and NoSQL Isn’t For Everyone”, I’d say that an even better one would be “SQL is scalable. SQL scalability isn’t for everyone. NoSQL isn’t for everyone either”.