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

7.3.2 System tuning
To measure the scaling success you need to generate a workload that meets the
following characteristics:
► Measurable
A metric that can be quantified, such as throughput and response time.
► Reproducible
The same results can be reproduced when the same test is executed multiple
times.
► Static
The same results can be achieved no matter for how long you execute the
run.
► Representative
The workload realistically represents the stress to the system under normal
operating considerations.
Workload should be discerned based on the specifications of the system. If you
are developing a data driven system, where 90% of the requests require a
database connection, this is a significantly different workload compared to a Web
application that makes 90% JSP and servlet calls, with the remaining 10% being
messages sent to a back-end store. This requires close work between the
application architect and the system architect.
Determine the projected load for a new system as early as possible. In the case
of Web applications, it is often difficult to predict traffic flows or to anticipate user
demand for the new application. In those cases, estimate using realistic models,
and then review the data when the system is launched to adjust expectations.
The first step in performance considerations is to verify that the application and
application environment has been adequately tuned. Tuning needs to be verified
at the application code layer, the network layer, the server hardware layer, the
operating system layer, and the WebSphere Application Server layer.
Network layer
Tuning at the network layer is usually done at a high level only. Take the time to
verify that port settings on the switches match the settings of the network
interfaces. Many times, a network device is set to a specific speed, and the
network interface is set to auto-detect. Depending on the operating system, this
can cause performance problems due to the negotiation done by the system.
Also, reviewing these settings establishes a baseline expectation as you move
forward with scaling attempts.
236 WebSphere Application Server V7.0: Concepts, Planning, and Design