[madhadron]

It's not about NoSQL vs SQL. Facebook's Tao is still backed by MySQL, so it's not like there's some intrinsic limitation. The issues are number of records examined to return a result, lock contention, sharding, and replication/consistency. NoSQL databases generally trade some of the conveniences of relational to be able to provide stronger properties in these aspects.

The limitations that Sarah Mei identifies as clownpants is using a 32 bit primary key for an identifier for an ephemeral thing. That is again nothing to do with SQL vs NoSQL. It would affect both of them the same way.

[databrecht]

I would go a step further, you can't even talk about NoSQL vs SQL. It's about database features, the join patterns, how scaling happens, both are overlapping more and more and will continue to overlap more. Products built on SQL are aiming to scale and 'NoSQL' is aiming to provide the features that SQL provides in a scalable manner. Her original statement was already quite confusing. A relational store doesn't necessarily mean SQL, many 'NoSQL' offer relations and are a perfect fit for social media or were even built to support this kind of applications :)