AS/400 Advanced Server Performance Tips

oday's client/server applications including such areas as Internet serving and Data Warehousing require a different balance of processor, memory and disk than our traditional interactive systems. The performance characteristics of the AS/400 server models work in favor of these client/server workloads. For the same investment you will see a better throughput for client/server and batch work and less throughput for interactive when compared with traditional AS/400 systems. The chart below shows the areas that benefit from a server model. Workloads that fall under the classification of interactive run more efficiently on the traditional AS/400 system models. It is important to note that all workloads will run on all systems. The system you choose for any given situation is strictly based on the workload characteristics which leads to a price performance advantage.

Server models have two relative performance ratings (RPR) and this confuses many people. You can think of the two ratings as a high and low rating for a single system. If your workload falls completely under the client/server category you will attain the higher performance rating. If your workload falls completely under the interactive category your system will perform at the equivalent of the lower rating. Most customer workloads fit somewhere in between. The graphs below show system performance ranging from high to low as the interactive workload is increased. On the CISC models as you add interactive work to the system your effective relative performance rating is decreased. The theory is the same for RISC but the actual performance curve is somewhat different. As a rule of thumb on the RISC models, if interactive performance will be more than 10% on a 40S or 50S, or more than 2% on a 53S your relative performance will be equivalent to the interactive or the lower performance rating.

Another change on the RISC models is the way the system reports interactive CPU utilization. With the RISC models you will see your interactive jobs and you will also see system tasks called CFINTn. Both of these items contribute to the interactive CPU utilization calculations. Interactive jobs on the server models cause a high percentage of time to be spent in the CFINTn tasks. QPFRADJ will adjust pool sizes and priorities to favor client/server work on the server models. QPFRADJ did not perform any special tuning for client/server jobs on the CISC servers.

The AS/400 Advanced Servers are ideally positioned for the new workloads being demanded from AS/400s these days. Areas such as Internet serving and Data Warehousing are ideal applications for server models. The design and tuning of the AS/400 server models allows for a much lower price for these new application areas. While growing the serving models IBM is not reducing their investment in the AS/400 system models which will continue to be the platform of choice for interactive or traditional applications. T < G

Jackie Jansen is an AS/400 Specialist and Consulting SE, providing national technical and marketing support for the AS/400 in Canada. Jackie frequently speaks at AS/400 Technical Conferences and User Group meetings.