Something like mysql slow query log could be useful when ready to make rethinkdb more ops friendly. Last night a friend was having issues with his mysql perfomance we ran mysql tunner and a few other things and got the load down by 10-20% but until i tunred on slow query log and saw there were no indexes and lots of queries doing full table scan it was not visible.

I dont think worrying about the slow query log being high performance should be an issue at the moment better to have it. If perfomance is an issue not sure if logging to a unix socket or named pipe would be faster does not need to have full profile out put just what the query looks like overall the time it took and what ever els super basic stuff.