Buffer Management › Tuning Buffers for Performance

Tuning Buffers for Performance

When to Add More Database Buffers

If your monitoring operations reveal contention among applications for use of your buffers, you may need to add more buffers. For example, you may create a new buffer and assign it to a file that is accessed frequently; files that are accessed infrequently can share buffers without incurring contention among applications.

To determine which files within a buffer are accessed most frequently, issue the DCMT DISPLAY STATISTICS BUFFER command with the FILE option. This will show the number of pages requested as well as the number of reads and writes issued for each file associated with a specific buffer.

When to Change the Database Buffer Page Size

You may have to change the buffer's page size if you associate different files with the buffer. The buffer's page size must be as large as the largest database page in any file associated with the buffer. Therefore, if new files assigned to the buffer contain larger database pages, the buffer page must be increased accordingly; likewise, if the files are removed from the buffer, you may be able to decrease the buffer page size to conserve memory resources.

When to Change the Number of Database Buffer Pages

You can use the buffer utilization ratio to determine if a buffer has the optimal number of pages. This ratio is the number of database pages requested to the number of database pages CA IDMS/DB reads from disk. A high ratio (above 2) indicates an effective buffer size. A lower ratio indicates that the buffer has too few pages.

You can use the DCMT DISPLAY STATISTICS BUFFER command to determine these values. You can also obtain them from the Performance Monitor, JREPORTs, and SREPORTs.