Making the partitions the same size

In most cases, Db2 divides the table space into logical pieces, called work ranges to differentiate these from physical pieces, based on the size of the largest physical partition of a given table. Suppose that a table consists of 10,000 pages and 10 physical partitions, the largest of which is 5000 pages. Db2 is most likely to create only two work ranges, and the degree of parallelism would be 2. If the same table has evenly sized partitions of 1000 pages each and the query is I/O-intensive, then ten logical work ranges might be created. This example would result in a degree of parallelism of 10 and reduced elapsed time.

Db2 tries to create equal work ranges by dividing the total cost of running the work by the logical partition cost. This division often has some left over work. In this case, Db2 creates an additional task to handle the extra work, rather than making all the work ranges larger, which would reduce the degree of parallelism.