Comment by zzzeek

the performance cost is going to be mostly in the kinds of queries it produces and how well they will be interepreted by the query planner. My understanding is that Pony is very heavy on subqueries and correlated subqueries, and the user is given extremely little leverage on being able to control the structure of queries rendered. Subqueries and especially correlated subqueries have the worst performance of all, especially on less mature planners like that of MySQL.