1. A computer implemented method comprising: observing interactions by each of a plurality of user of an online system, wherein the observed interactions are indicative of an affinity of the users towards an application of a plurality of applications; determining, by the online system, an affinity score for the application based on an aggregate value based on the observed interactions by the plurality of users; determining, by the online system, an allocation of a channel resource for the application based on the affinity score, the allocation specifying a threshold usage of the channel resource by the application; and limiting a rate at which the application is allowed to send messages via the channel resource, wherein the rate is limited to the threshold usage of the channel resource specified by the allocation.