1. A method of computing a query response time of a multi-tier system, the method comprising: determining a network transmission time of data transfers between an end user and each of a plurality of tiers; calculating a first response time of a first tier using a first model; calculating a second response time of a second tier using a second model that is different than the first model, the second tier including at least two partitions; determining an aggregate response time based on at least the network transmission time, the first response time, and the second response time.