1. A network control system for generating physical control plane data for managing a set of managed forwarding elements that implements forwarding operations associated with a logical datapath set, the system comprising: a first controller instance operating on a controller computer having one or more processing units for executing the first controller instance and a memory for storing the first controller instance, the first controller instance for (i) receiving input data defining the logical datapath set and performing a first conversion of data for the logical datapath set to generate intermediate data tuples for the logical datapath set, and (ii) distributing the intermediate data tuples to a set of hosts on which the set of managed forwarding elements operates; and a second controller instance operating on a particular one of the hosts for (i) receiving the intermediate data tuples for the logical datapath set and (ii) converting the intermediate data tuples into physical control plane data for use by a managed forwarding element operating on the particular host.