Addressing OLTP Solutions with CICS: The Transaction Server ... - Ibm

3.4.1 Overall Objectives
3.4.2 Capacity Planning
better performance than the second because the latter has to remotely access
the data. There may be perfectly valid reasons for setting up a system in the
manner of the second. However, it cannot perform identically to the first system
because of the additional processing and network delays. This example
demonstrates that no amount of system tuning can overcome a poor initial
design for either the CICS for AIX configuration or the application.
Although the focus in this section is on CICS, you should remember that there
are other components in a system, such as an RDBMS or an interconnected
CICS system. Adding a new application not only affects the CICS system in
which it runs but also these related components.
You must put a lot of thought and effort into the early planning stages, and
consult widely, talking to people from operations, CICS systems programming,
database administration, application design, capacity planning, and user support
groups. Doing this will greatly improve the likelihood that the configuration will
work as intended, with the expected results. It is essential to think through the
proposed configuration from the user interface to how operations will run and
provide problem determination for the system. If the proposed region is to
provide a service for multiple applications, you must walk through the
configuration for each application to ensure that all of its needs are met.
Sometimes in implementing an aspect of a CICS system or an application,
options are not available. You are forced to use a certain type of CICS client
because the users already have a PC installed running OS/2 rather than an
X-station, for example. In such instances it becomes a case of determining
whether the function is available in the product to support the need rather than
trying to evaluate the merits of the alternatives.
Have a clear view of what is required from the new configuration, what the
primary and secondary objectives are. Decide whether system throughput, user
response time, or system availability is most important. Whatever your
requirements, be clear about them.
Where new CICS regions are being introduced as part of the introduction of a
new application or where a new application is being added to an existing CICS
region, it is important to undertake some capacity planning. Understand the
processing requirements of the new application before you discover that it is
flooding your existing configuration and could affect users of other applications.
This work will help you understand which machine resources, such as CPU and
disk space, are required. It will also give you something to compare the actual
results to later on. This is important for a completely new application for which
historical information is not available.
Before beginning your capacity planning:
• Identify the different types of business transactions
• Understand the ratio of CICS transactions to business transactions
• Determine the likely and maximum transactions rates
• Understand where the application data will be held
• Develop a profile for each type of transaction:
− Map out the CICS services that will be required
− Identify the recoverable resources
Chapter 3. CICS for AIX 39