Systems and methods for, among other things, a utilization based load balancing system which controls the distribution of queries to an information retrieval system made up of a network of server clusters. In one embodiment, a server cluster allocates computational resources among computational tasks. These computational tasks are replicated across a given server cluster, typically such that those computational tasks requested more frequently have more replicas, and more resources allocated to them to fulfill the requests. The system applies a utilization metric to determine how much capacity a given task has available and uses this determination to determine the capacity available for the cluster as a whole. Load balancing is achieved by re-directing queries to another cluster in response to the utilization value for a given cluster reaching a threshold.