POSort always use ascending order. We shall obey the sort order as specified in the script.
For example, the following script does not do the right thing if we turn off secondary sort (which means, we will rely on POSort to sort):
If we run it using the command line "java -Xmx512m -Dpig.exec.nosecondarykey=true -jar pig.jar 1.pig".
The sort order for D is ascending.