Using IBM Application Development Tools for z/OS and OS/390

200 Using IBM Application Development Tools for z/OS and OS/390

5.1 Why does an application developer need a profiler?

We were recently asked by a reviewer of the Application Monitor documentation what an

application programmer would use something like this tool for. This short introduction is

intended to answer that question.

5.1.1 During application development

The most straightforward use of the profiler is in situations where your code is not meeting its

intended performance targets. A profiler can be used to determine which routines are used

the most, and what would benefit from examination for performance tuning.

The next obvious use for a profiler is for determining the location of a “supposedly” infinite

loop. A profiler such as Application Monitor can be used to actively monitor the application

while it is running and “drill down” through the list of modules to the assembler instruction or

the COBOL/PLI source line.

There is yet another use for a profiler during development. While programming an application,

a programmer often ends up using code developed by another developer. This can leave a

programmer dangerously lacking in information about the performance of the code. If two

implementations are possible, a profiler can be used to determine which one will perform best

— either by using it to compare both implementations, or more likely, by using it to look at the

performance of functions you will be using and determine which functions run faster.

5.1.2 During application test

Most application development projects have either stated or implied performance targets.

A regimen of performance test scenarios is especially common. The profiler tool can be used

to provide more information; for example, suppose that an application runs 25% slower. The

tool could be used to determine which part of the application has degraded or if it was an

overall degradation. Comparative reports could also be used to monitor changes in the

application’s performance.

5.1.3 During application service

If a customer reports a problem with performance, a profiler is the perfect tool to help the

service professional narrow down the cause and pinpoint the solution.

5.1.4 During application maintenance

It is a fact of modern development that the person who maintains a given application is not

necessarily the person who wrote it. It is also true that the performance characteristics of an

application can change during its service lifetime.

A profiler such as Application Monitor can help stop the performance loss that often occurs

during maintenance. In an ideal world the location of the hot spots and heavy loops in a given

application would be known and documented for all follow on developers. We rarely see such

an ideal world. An application programmer can use this tool to determine where the hot spots

or heavy loops are in the application. The information on where the performance bottleneck is

located can then be taken into consideration when putting in a fix. For example, the developer

could find out where the heavy loop is, and then do whatever is possible to avoid adding code

to that loop when fixing the problem.

Application Monitor could also be used after a tentative fix that seems to degrade

performance to help find the cause of that degradation.