Is this SQL databases or No-SQL?

Well, sometimes what he says is true. I did spend months -- actually, most of a year -- tuning a large database-backed Oracle system for better performance. About 20% of that was DML and even some DDL rewriting: perhaps twenty out of a million-plus queries in this system had bad performance. This was mostly down to places where the programmer had tried to be 'clever', Pick-style, and was denying the optimizer a chance to work (e.g. one place was repeatedly reissuing similar queries twelve times over rather than using an intermediate table and a suitable join to do all the work at once). Rewriting such queries to let the optimizer chew at them fixed about 80% of the speed problems we were seeing, speeding up the system by a factor of perhaps a hundred to a thousand under the relevant problematic workloads.

(The rest of the sloth? Maybe I could have fixed it with query rewriting, but with no low-hanging fruit it would have meant rewriting hundreds or thousands of queries. I chose to add application-side caches instead. All the speedup, none of hte pain.)