Performance trade-offs

Table 1 is a summary of the techniques described in this document for improving DFSORT performance. In many cases (use of Blockset is a notable exception), an improvement in performance is not free. The figure summarizes these potential trade-offs: increased paging, increased swapping, increased CPU time, and changes needed to applications.

For example, to use this figure, assume you want to improve the elapsed time for a DFSORT application. A number of techniques exist to choose from, ranging from ensuring that DFSORT uses Blockset to modifying the way the application uses DFSORT. You can decide which technique, or combination of techniques, is appropriate based on the effort required and the trade-off, if any, you are prepared to accept.

Table 1. Summary of Potential Performance Trade-Offs
Improvement Area	Technique	Potential Trade-Offs
Improvement Area	Technique	Increased Paging	Increased Swapping	Increased CPU Time	Change Application
CPU Time	Use Blockset
	Increase Virtual Storage	Y	Y
	Use appropriate large block sizes for input and output data sets
	Use DFSORT functions and exits				Y
Elapsed Time	Use Blockset
	Use memory object sorting
	Use dataspace sorting
	Use multiple work data set devices
	Increase Virtual Storage	Y	Y
	Use Hipersorting			Y
	Use VIO data sets	Y		Y
	Use appropriate large block sizes for input and output data sets
	Use DFSORT functions and exits				Y
	Use striping
I/O Activity	Use Blockset
	Increase Virtual Storage	Y	Y
	Use Hipersorting			Y
	Use memory object sorting
	Use dataspace sorting
	Use appropriate large block sizes for input and output data sets
	Use DFSORT functions and exits				Y
	Use striping
Work Data Set Space	Use Hipersorting			Y
	Use memory object sorting
	Use dataspace sorting
	Increase Virtual Storage	Y	Y
Specify number of records when appropriate				Y