System resources

The purpose of tuning DFSORT is to use system resources more efficiently. This is important at most sites, since there are usually too many demands made for limited resources. Although DFSORT automatically optimizes many of its tuning decisions, there are additional actions which a site and its DFSORT users can take to further improve DFSORT performance. These actions depend on the priority given to various performance objectives.

Different sites and programmers define efficient performance in different ways. A site with a primarily batch environment or an application programmer with a single task to complete probably measures performance based on elapsed time. Alternatively, a site experiencing high CPU usage or a programmer who is charged based on CPU time is more likely to evaluate efficiency in terms of reduced CPU time.

While improved performance is the objective of tuning, often it is necessary to compromise. That is, improving the use of one system resource can have a negative impact on other resources, in much the same way that giving more resources to one application can make it perform much better at the expense of degrading the performance of other applications that are competing for the same resources.

The main trade-offs that you should consider are among:

Processor Load: Accounting charges are often based on the number of CPU service units used by a job or address space. The more CPU time used, the higher the charges. Reducing a job's CPU time not only reduces these charges, but also enables other jobs competing for the same CPU resource to complete sooner.
Paging Activity: System paging activity reflects how the system is managing central storage to meet the virtual storage requirements of applications and user programs. Paging is the process of moving virtual storage pages from central storage to auxiliary storage, and takes a large amount of elapsed time to perform.
System paging activity can increase elapsed time for user programs. If the activity is too high, the system reduces its workload by reducing the number of jobs running, and might suspend processing of some jobs (known as swapping) until the paging activity returns to an acceptable level. The result is that the system spends more time managing virtual storage, while many user programs take longer to complete.
I/O Activity: Some accounting charges are based on the I/O performed by a job. This is frequently measured by execute channel program (EXCP) counts. While EXCP counts might not represent a completely accurate usage of I/O resources, they are important to many users and sites, and steps can be taken to reduce them.
Elapsed Time: Elapsed time is likely to be most important for sites with a limited batch window, where processing of particular applications has to be completed within a certain period. It is also important to users whose productivity depends on having their applications complete as soon as possible.
Disk Utilization: In environments where disk space is constrained, the amount of auxiliary storage required by an application is a primary concern. For DFSORT applications, this usually involves the efficient use of output and work data sets.