1. An event-categorizing subsystem within an event-collection-and-event-processing system that includes one or more computer systems, each having one or more processors, one or more memories, and one or more mass-storage devices, the event-categorizing subsystem executing on the one or more processors to: receive a stream of events, each event comprising a set of key/value pairs, the stream stored in one or more memories and/or mass-storage devices; apply a seeded global/local-topic Latent Dirichlet Allocation analysis to a subset of events of the stream of events in order to assign each event of the subset of events to one of K different topics, where K is an integer value greater than 1; generate a topic signature for the events assigned to each topic; and for each subsequently received event, computing a score for the received event with respect to each of the K topic signatures, assigning the received event to a topic based on the computed scores, storing, in one of the one or more memories, an indication of the topic to which the event is assigned, and forwarding the event, including the indication of the topic to which the event is assigned, to an event-processing subsystem.