Work units are received into, and processed from, holding queues. A partition, associated with a unique holding queue, is assigned to each work unit stored in a given holding queue, according to a partitioning rule. Work units are separated from each holding queue into one of two or more other queues stored in the same storage as that holding queue. A ready queue (relocation queue) is for each work unit whose assigned partition is (is not) associated with the holding queue in which it is stored. Each work unit in each relocation queue is relocated to the holding queue associated with the partition assigned to that work unit. The work units are repartitioned in response to a change in the partitioning rule to a new partitioning rule before the holding queues are empty.