Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for processing event data. In one aspect, a method includes assigning events to event bundles based on timestamps associated with the events. Each event bundle contains events having timestamps that are within a pre-specified period of time. Event batches are created, where each event batch includes a pre-specified number of event bundles. A first event batch is provided to a first computing group and a second computing group. The first computing group is configured to perform a first processing stage, and the second computing group is configured to perform a second processing stage. A determination is made that a threshold number of the event bundles in the first event batch have been processed by the first computing group. In response to the determination, a second event batch is provided to each of the computing groups.