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

3.4.3 Configuration
3.4.4 Managing the Work
40 CICS for AIX as the Transaction Server
− Understand how application data will be accessed from within the
application. This may not be determined by CICS but by an RDBMS. It
is still important to understand though
− Understand the amount of logical and physical I/O
− Understand the level of logging involved
• Determine which other software components, such as an RDBMS or a
remote system, are involved. What is the projected load of the new
applications? Can they accommodate the load?
Capacity planning will enable you to see whether the expected work can be
accommodated by the current processing power and I/O capacity or whether
additional machines will be required. If new machines are required, you have to
determine their size. There are extremes of effort in performing capacity
planning. A minimal level of effort would be to look at the application design
and estimate the volume of I/O and the CPU requirements. The other extreme
would be to model in quite some level of detail, the clients, the CICS for AIX
region, the RDBMS, and possibly the network load.
Consider the other processes that may be competing with this CICS for AIX
region; for example, is a large amount of batch work processed on the same
machine?
To implement new CICS systems, you first have to form an idea of what the
configuration is going to be, that is, you have to know how many regions on how
many processors are required. The decision may or may not be straightforward.
It is likely to be influenced by a number of factors:
• The likely processing power required. From your application capacity
planning, you can determine whether you will have a single or multisystem
implementation.
• The design requirements of the proposed systems. If high availability of the
application is a key requirement, consider implementing multiple regions
capable of running the application and managing the workload. See 8.5.1,
“Maximizing the Benefit” on page 121 for more details of this approach.
• If the new application is incompatible with existing applications or has
special operational or security requirements, you will have to implement
another CICS region.
• If the aim is to exploit a parallel database, the recommended approach is to
have multiple CICS systems capable of accessing the database (see 8.5.1.3,
“Using an SP Processor” on page 123).
In implementing new CICS systems, you may find that applications are split over
more than one CICS system for reasons of availability or because the processing
capacity required exceeds that available from a single machine. Incoming user
transactions have to be distributed over the available CICS systems. The
distribution of work is an awkward problem that must be resolved. You must
understand how you are going to deal with it in your environment.
The incoming work must be distributed in such a manner that no one CICS
system is flooded with more work than it can process. One approach might be
to distribute the number of users evenly over the available systems so that
groups of users access particular systems. The allocation of work is performed
by controlling the number of users who access the system. Some groups of