Database buffers and CPU time

Products

• IDMS

Issue/Introduction

Is there a CPU overhead in case the number of pages in a database buffer are increased?

Environment

Release: All supported releases.

Resolution

Increasing the buffers has no effect on CPU. The big problem could be z/OS paging. If that doesn't happen, then there should be no noticeable change in CPU. 

IDMS uses a hashing algorithm to find database pages, so the number of pages doesn't matter. It also builds bit lists, which depend on the number of pages. But the access of the bit lists should only add a minor amount of CPU, most likely not detectable. 

The big advantage of large buffers is the re-access of a database page that's still in the buffer pool. The bigger the buffer pool, the longer the page stays in the buffer. If that page is accessed many times, then the I/O is reduced. If it's only accessed once or twice, then a large buffer pool has no advantage over a small buffer pool.

Additional Information

Buffer Management