Performing capacity planning

Other topics discuss short- or medium-range planning for changes in the processing requirements of your IMS online design. However, you might want to examine the long-term adequacy of your design.

For example, if you extrapolate trends in workload, will enough computing power be available?

You can use:

As a result of your performance monitoring, you can establish transaction profiles. One part of these profiles can be a trend analysis. You must determine mean and peak arrival rates: currently predicted, sample actuals, and future expectations. The overall processing summary can be taken from the IMS Monitor Run Profile report.

One way to investigate limiting capacity is to extrapolate the volume of transactions. You can establish a trend from percentage processor usage for several monitor points. A common observation from performance measurements indicates that the increase in machine cycles is nearly linear with the increase in transactions per second on systems dedicated to IMS. If you plot several points, showing increasing transaction loads against percentage utilization, you can extrapolate to find your limiting number of transactions as the percentage utilization approaches 100%.

You can also see if a predicted maximum workload corresponds to a utilization that is below a practical upper limit. The workload is estimated by weighing the current overall profile with additional transactions.

In making such predictions, you should have adequate virtual storage and an I/O configuration sufficient to handle the increased transaction load. A careful consideration of remaining available I/O and virtual storage resources is necessary, because contention for these elements has a more severe impact on performance than the level of processor utilization.

If you are managing a large system running under z/OS®, you might want to reduce your requirements for CSA. You can plan to use the DL/I separate address space and, if necessary, local storage for IRLM for lock management. Using your projected workload, you might still want to estimate virtual storage with various configurations.