Intel 7xx Servers, 170 Servers manual User Pool Faulting Guidelines, Setobjacc Set Object Access

files of differing characteristics are being accessed. The pool attribute can be changed from *FIXED to *CALC and back at any time, so making a change and evaluating its affect over a period of time is a fairly safe experiment.

More information about Expert Cache can be found in the Work Management guide.

In some situations, you may find that you can achieve better memory utilization by defining the caching characteristics yourself, rather than relying on the system algorithms. This can be done using the QWCCHGTN (Change Pool Tuning Information) API, which is described in the Work Management API reference manual. This API was provided prior to the offering of the *CALC option for the system. It is still available for use, although most situations will see relatively little improvement over the *CALC option and it is quite possible to achieve less improvement than with *CALC. When the API is used to adjust the pool attribute, the value that is shown for the pool is USRDFN (user defined).

SETOBJACC (Set Object Access)

In some cases, the object access performance is improved when the user manually defines (names a specific object) which object is placed into main storage. This can be achieved with the SETOBJACC command. This command will clear any pages of an object that are in other storage pools and moves the object to the specified pool. If the object is larger than the pool, the first portions of the object are replaced with the later pages that are moved into the pool. The command reports on the current amount of storage that is used in the pool.

If SETOBJACC is used when the QPFRADJ system value is set to either 2 or 3, the pool that is used to hold the object should be a private pool so that the dynamic adjustment algorithms do not shrink the pool because of the lack of job activity in the pool.

Large Memory Systems

Normally, you will use memory pools to separate specific sets of work, leaving all jobs which do a similar activity in the same memory pool. With today's ability to configure many gigabytes of mainstore, you may also find that work can be done more efficiently if you divide large groups of similar jobs into separate memory pools. This may allow for more efficient operation of the algorithms which need to search the pool for the best candidates to purge when new data is being brought in. Laboratory experiments using the I/O intensive CPW workload on a fully configured 24-way system have shown about a 2% improvement in CPU utilization when the transaction jobs were split among pools of about 16GB each, rather than all running in a single memory pool.

19.6 User Pool Faulting Guidelines

Due to the large range of AS/400 processors and due to an ever increasing variance in the complexity of user applications, paging guidelines for user pools are no longer published. Even the system wide guidelines are just that...guidelines. Each customer needs to track response time, throughput, and cpu utilization against the paging rates to determine a reasonable paging rate.

There are two choices for tuning user pools:

1.Set system value QPFRADJ = 2 or 3, as described earlier in this chapter.

2.Manual tuning. Move storage around until the response times and throughputs are acceptable. The rest of this section deals with how to determine these acceptable levels.

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