Optimizing System Performance

Optimizing Memory Usage under OpenVMS

You can make tradeoffs between memory and other resources. This is explained in Data Set I/O under OpenVMS and External I/O under OpenVMS. To optimize the I/O subsystem, you need to use more, larger buffers. These buffers are allocated out of your available virtual address space and must share your physical address space (that is, your working set) with the other memory demands of your SAS session.

Therefore, optimization of other resources is often at the expense of using more and more memory. If memory is your critical resource, there are several things you can do to reduce the dependence on increased memory. However, most of these techniques are at the expense of increased I/O processing or increased CPU usage.

Increasing the values of the MBC= and MBF= external I/O statement options, the CACHESIZE= option, and the BKS= option enables you to optimize the I/O subsystem by reducing the number of disk I/O operations necessary to reference the data. But reducing the number of disk I/O operations uses more memory. If you are operating in a memory-constrained environment, you need to reduce these values to minimize memory usage.

The size of your I/O buffers depends on your working set size. It is important not to increase I/O buffers up to the point that you exhaust your available working set. If you do this, you will notice an increase in the page fault rate for your job.

Using the LOADLIST= System Option

Job type	Any job that accesses a SAS image.
User	SAS programmer.
Usage	The LOADLIST= system option reports the SAS images that were used the most often.
Benefit	You can optimize memory usage by installing the most heavily used images as known images.
Cost	There is no performance penalty.

To optimize memory usage, ensure that images that are used most often are installed as known images to the OpenVMS operating environment. If you use the LOADLIST= system option, SAS reports which images were used most often. If you install the most heavily used images as known images, they do not require additional physical memory if used by multiple users. These images should be installed with the /SHARED option. For information about using the INSTALL utility, see System Start-Up under OpenVMS. For more information, see LOADLIST= System Option: OpenVMS.

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