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We will discuss this case by example using the task topology shown below. Assume exactly two slots to be available to the cluster. Furthermore, all data exchanges are assumed to be pipelined, and all tasks are in the same slot sharing group.

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All tasks are scheduled at the same time and compete for the available slots. If, for example, A2 and A4 are assigned slots, all slots of the cluster will be occupied indefinitely. Note that A2 and A4 will not be able to finish without B1 and B2 running. If we had scheduled (A1, B1) and (A2) to the two available slots, the upper region could have actually finished. Note that (A1, B1) only occupies one slot due to slot sharing.

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