Spotlight on SAP ASE 2.12 - User Guide

Physical Reads chart

Use this chart to graphically compare the amount of physical reads between each pool for the cache selected.

Tuning the performance of a data cache's buffer pool configuration can have a dramatic effect on application response times. A poorly configured cache pool can have the reverse effect on an Adaptive Server.

• A pool that is unused hurts performance. If you add a large I/O (16K) pool, but none of your queries use it, you have taken space away from the small I/O (2K) pool. The 2K pool's cache hit ratio is reduced, and I/O is increased.

• A pool that is overused hurts performance. If you configure a 16K pool with too little space, and virtually all of your queries use it, I/O rates are increased. The respective 2K cache will be under-utilized, while pages are rapidly cycled through the 16K pool. The cache hit ratio in the 16K pool will be very poor.

• If you balance your pool utilization within a cache, performance can increase dramatically. Both large I/O (16K) and small I/O (2K) queries experience improved cache hit ratios. The large number of pages often used by queries that perform 16K I/O do not flush 2K pages from disk. Queries using 16K will perform approximately one-eighth the number of I/Os required by 2K I/O.

*Available only in Adaptive Server versions 12.5.0.3 or later