Intel AS/400 RISC Server, 170 Servers Tuning Parameters for Batch, Expert Cache, Job Priority

3.3 Tuning Parameters for Batch

There are several system parameters that affect batch performance. The magnitude of the effect for each of them depends on the specific application and overall system characteristics. Some general information is provided here.

yExpert Cache

Expert Cache did not have a significant effect on the Commercial Mix batch workload. Expert Cache does not start to provide improvement unless the following are true for a given workload. These include:

y the application that is running is disk intensive, and disk I/O's are limiting the throughput. y the processor is under-utilized, at less than 60%.

y the system must have sufficient main storage.

For Expert Cache to operate effectively, there must be spare CPU, so that when the average disk access time is reduced by caching in main storage, the CPU can process more work. In the Commercial Mix benchmark, the CPU was the limiting factor.

However, specific batch environments that are DASD I/O intensive, and process data sequentially may realize significant performance gains by taking advantage of larger memory sizes available on the RISC models, particularly at the high-end. Even though in general applications require more main storage on the RISC models, batch applications that process data sequentially may only require slightly more main storage on RISC. Therefore, with larger memory sizes in conjunction with using Expert Cache, these applications may achieve significant performance gains by decreasing the number of DASD I/O operations.

yJob Priority

Batch jobs can be given a priority value that will affect how much CPU processing time the job will get. For a system with high CPU utilization and a batch job with a low job priority, the batch throughput may be severely limited. Likewise, if the batch job has a high priority, the batch throughput may be high at the expense of interactive job performance.

yDynamic Priority Scheduling

See 19.2, “Dynamic Priority Scheduling” for details.

yApplication Techniques

The batch application can also be tuned for optimized performance. Some suggestions include:

y Breaking the application into pieces and having multiple batch threads (jobs) operate concurrently. Since batch jobs are typically serialized by I/O, this will decrease the overall required batch window requirements.

y Reduce the number of opens/closes, I/Os, etc. where possible.

yIf you have a considerable amount of main storage available, consider using the Set Object Access (SETOBJACC) command. This command pre-loads the complete database file, database index, or program into the assigned main storage pool if sufficient storage is available . The objective is to

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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