A system and methods for queuing processing jobs. The system is configured to receive a processing job associated with a user; score the processing job; apply one or more bounds; add the processing job to a queue; order the queue based on scores of processing jobs in the queue; and sample processing jobs from the queue for dispatch for processing. Sampling the jobs from the queues can comprise updating scores, updating application of bounds, and updating ordering of the queue; reading a batch of processing jobs from a top of the queue; attempting to dispatch the processing jobs of the batch for processing; removing from the queue any dispatched processing jobs; increasing the batch size by a constant factor; determining whether a maximum batch size is reached, or all processing jobs in the queue were in the batch.