1. A system comprising: a database; and a cache layer comprising one or more cache nodes, the one or more cache nodes operative to: maintain in a memory one or more data structures storing association information describing associations between nodes in a graph a plurality of distributed cache clusters for storing information in the form of a graph, the graph comprising a plurality of nodes, each uniquely identified by a node identifier, and edge information indicating associations between nodes; respond to queries for associations between nodes in the graph by accessing the memory; and forward other queries to the database for processing.