MAXOBUF parameter

Maximum open buffers per user

Summary

Default value

4

Parameter type

System

Where set

On User 0's parameter line

Related products

All

Introduced

Model 204 V5.1

Description

User's can have open buffers only while in a server. The maximum value of MAXOBUF is 255. Model 204 uses the extra open buffer limit above four to try to do fast page reads on frequently accessed pages. Adjusting the MAXOBUF setting provides the best results in an MP/204 environment, but there may be some performance advantages in a non-MP environment.

You can regard the MAXOBUF parameter as a user-level working set size for disk buffer pool pages. However, consider the following disadvantages of setting the value of MAXOBUF too high:

• First, a too-high value can reduce the accuracy of the Model 204 LRU algorithm for disk buffer pool pages.
• Second, and more importantly, a too-high value can actually increase CPU overhead, because of relatively long chains of open pages that must be scanned for a fast read.

Rocket Software recommends that you test for the optimal setting of MAXOBUF at your site by gradually increasing MAXOBUF until the CPU statistic compared to the work accomplished stops decreasing and starts to increase, or the DKPRF/DKPR statistics ratio stops changing significantly.