WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

4.5.5 Production system tuning
This is where you apply all the performance, scalability, and high availability
considerations in production. Tuning the system is an iterative process that
involves optimizing WebSphere parameters to suit your runtime environment.
Important: To perform tuning in the production environment, have the final
version of code running. This version should have passed performance tests
on the integration environment prior to changing any WebSphere parameters
on the production system.
When changing a production environment, use some standard practices:
► Change only one parameter at a time.
► Document all changes.
► Compare several test runs to the baseline.
Changes between test runs should not differ by more than a small percentage to
preclude introducing new problems that you might need to sort out before you
continue tuning.
As soon as you finish tuning your production systems, apply the settings to your
test environments to make sure that they are similar to production. Plan to rerun
your tests there to establish new baselines on these systems and to see how
these changes affect the performance.
Keep in mind that you often only have one chance to get this right. Normally, as
soon as you are in production with your system, you cannot run performance
tests on this environment any more, simply because you cannot take the
production system offline to run more performance tests. If a production system
is being tested, it is likely that the system is running in a severely degraded
position, and you have already lost half the battle.
Note: Because it is rare to use a production system for load tests, it is usually
a bad idea to migrate these environments to new WebSphere versions without
doing a proper test on an equivalent test system or new hardware.
After completing your first performance tests and tuning the WebSphere
parameters, evaluate your results and compare them to your objectives to see
how all of this worked out for you.
112 WebSphere Application Server V7.0: Concepts, Planning, and Design