Performance expectations of the user

When assessing the performance of a DP system, the user is generally interested in:

• the time it takes for the system to respond to requests,

• how many requests the system can handle within a given period of time, and

• what resources are used.

The performance level of the hardware (e.g. the number of instructions processed per second) and of the operating system (e.g. task management efficiency) are generally of secondary interest.

Parameters for online use

A distinction is made between inquiry-and-transaction mode and timesharing mode:

In inquiry-and-transaction mode the terminal users can communicate only with programs which are specific to a given application. Normally, a large number of users interact with a relatively small number of application programs.

In timesharing mode the terminal users enter their own application programs for interactively processing a given task. The application programs are generally controlled by system programs for creating, testing and updating files and programs.

In both inquiry-and-transaction mode and timesharing mode, the unit of DP operation is a transaction.

The transaction time is the delay between the arrival of the input at the host and the output of the acknowledgment. The DP system can output several responses with different response times for a single transaction. If resources are not released when a transaction is completed but are reserved for the next transaction, the transaction is known as a multistep transaction.

The sum of single-step and multi-step transactions required for handling one application is called an operation.
The characteristic criteria for describing performance expectations are:

• Transaction rate
  Sum of all successfully completed transactions per unit of time

• Response time
  Time required for processing by the DP system

• Number of simultaneously active users.

The monitored values for these characteristics are determined in SM2 by the monitoring program BCAM-CONNECTION ("Monitored data on connection sets"), RESPONSETIME ("Monitored data on the BCAM pool") and UTM ("Monitored data on openUTM applications").

Batch processing criteria

In batch processing, the unit of DP processing is a job.

• Throughput rate
  Number of successfully processed jobs per unit of time

• Dwell time
  Time required for processing a job

For the individual user, a satisfactory performance (short response time, short dwell time) is obtained if the required resources are available when they are requested. This requirement can easily be meet if utilization of the requested resources (in particular of the input/output devices) is kept to a minimum.

The DP system performance, on the other hand, is characterized by the transaction and throughput rates, where maximum utilization of the resources is desirable for economic reasons.

These contradictory performance requirements relating to resource utilization can be fulfilled only by carefully planning the workload and the associated resource requirements.