I have never worked at true "web scale", so my experience may or may not apply to such scenarios. I tend to make a more or less fully normalized structure, and

I have never worked at true "web scale", so my experience may or may not apply to such scenarios. I tend to make a more or less fully normalized structure, and introduce aggregated data outside of the core database. It is essentially introducting eventual consistency, for performance critical data. This data can be stored in a database or a cache layer in front of the database if it is accessed frequently enough to keep it off the disk all the time.