[jhgb]

> It is amazing how many large-scale applications run on a single or a few large RDBMS. It seems like a bad idea at first: surely a single point of failure must be bad for availability and scalability?

I'm pretty sure that was the whole idea of RDBMS, to separate application from data. You badly lose the very moment when some of your data is in a different place -- on transactions, query planning, security, etc. -- so Codd thought "what if even different applications could use a single company-wide database?" Hence the "have everything in a single database" part should be the last compromise you're forced to make, not the first one.