> This is written as speculation of course, but it matches some long-time "conventional wisdom", that most Rails apps spend most of their time on I/O waiting fo

> This is written as speculation of course, but it matches some long-time "conventional wisdom", that most Rails apps spend most of their time on I/O waiting for something external. > Can we put this rumor to rest? You have only given one example though. What rumor is there to put to rest? I think the statement is still accurate: "most Rails apps spend most of their time on I/O waiting for something external" To your specific concerns though - I have also see ActionView and ActiveRecord casting take up non-trivial amounts of time (I recall a situation in a past job where the mysql driver being notoriously bad with allocations of enums - probably our own doing however).