... the MySQL databases serving English Wikipedia alone reach a daily peak of ~50k queries/second. Most are read queries served by load-balanced slaves, depending on consistency requirements. 80% of the English Wikipedia query load (up to 40k qps) are typically handled by just two database servers at any given time. Our most common query type (40% of all) has a median execution time of ~0.2ms and a 95th percentile time of ~50ms.
Thank you Asher Feldman and the Wikimedia foundation for publishing info like this.