In a parallel partition scan, multiple worker processes completely scan each partition in a partitioned table. One worker process is assigned to each partition, and each process reads all pages in the partition. Figure 25-1 illustrates a parallel partition scan.
Figure 25-1: Parallel partition scan
The parallel partition scan operates faster than a serial table scan. The work is divided over several worker processes that can execute simultaneously on different engines. Some worker processes can be executing during the time that others sleep on I/O or other system resources. If the table partitions reside on separate physical devices, I/O parallelism is also possible.