Quick Sort

A quick sort does nothing until it receives the last row of its input, and it produces no output until the sort is complete, so the time required to perform the sort cannot overlap with either the time to process its input or to produce its output. Under normal circumstances, this type of sort is expected to take the least CPU time. There are rare exceptional cases where it can perform badly (the famous "median-of-three killer" is an example) but you are very unlikely to hit these by chance.

On a Thor cluster where each node has multiple CPUs or CPU cores, it is possible to split up the quick sort problem and run sections of the work in parallel. This happens automatically if the hardware supports it. Doing this does not improve the amount of actual CPU time used (in fact, it fractionally increases it because of the overhead of splitting the task) but the overall time required to perform the sort operation is significantly reduced. On a cluster with dual CPU/core nodes it should only take about half the time, only about a quarter of the time on a cluster with quad-processor nodes, etc.