> Then how is it better than simply using another webhead? Data locality. > In any case, we need to do heavy calculations AND transactionally update some stat

> Then how is it better than simply using another webhead? Data locality. > In any case, we need to do heavy calculations AND transactionally update some state. In that case, I'd have the app server connect to both master and slave, run the heavy calculations on the slave the same way, and then send the updates to the master.