"DBMS are optimized for the fastest possible disk I/O." I think that's disputable. DBMSes are designed for a number of considerations and it's not hard to dem

"DBMS are optimized for the fastest possible disk I/O." I think that's disputable. DBMSes are designed for a number of considerations and it's not hard to demonstrate how alternatives can outperform a DBMS in terms of disk I/O and general performance. Consider an HTTP request that modifies records. A typical DBMS-backed app will write all the changes to disk whereas a prevalent system (AKA object prevalence) need only write "POST /someurl arg1=value1:arg2=value2:..." or some equivalent. The data is updated in RAM with a write to only one or two disk sectors in the majority of cases, no communication with a DBMS, no construction and parsing of SQL, and none of the other overhead. A typical prevalent system will be orders of magnitude faster than the DBMS-backed equivalent, and simpler to boot. Object prevalence doesn't offer a query language and has different scalability considerations, but it would take an absurdly broken design for a DBMS to outperform it.