(Hopefully) gone are the days when DBs are spending the bulk of their time blocking in I/O waiting for spinning disks to spin. They spend a lot of intelligence

(Hopefully) gone are the days when DBs are spending the bulk of their time blocking in I/O waiting for spinning disks to spin. They spend a lot of intelligence on keeping active tuples paged-in, and memory sizes are exponentially bigger than they used to be, and intelligent query optimization is going to do as much as it can into memory and then apply join algorithms which... are usually sorts. And even writes, there's sorting there. An LSM or a B-epsilon-tree, etc. they're doing sorting and ordered key traversals before paging out.