MAXOBUF parameter: Difference between revisions
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{{Template:MAXOBUF parameter subtitle}} | |||
==Summary== | ==Summary== | ||
<dl> | <dl> | ||
| Line 10: | Line 11: | ||
<dd>All | <dd>All | ||
<dt>Introduced | <dt>Introduced | ||
<dd><var class="product">Model 204 | <dd><var class="product">Model 204 V5.1</var> | ||
</dl> | </dl> | ||
==Description== | ==Description== | ||
<p>User's can have open buffers only while in a server. The maximum value of MAXOBUF is 255. <var class="product">Model 204</var> 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.</p> | <p>User's can have open buffers only while in a server. The maximum value of <var>MAXOBUF</var> is 255. <var class="product">Model 204</var> uses the extra open buffer limit above four to try to do fast page reads on frequently accessed pages. Adjusting the <var>MAXOBUF</var> setting provides the best results in an [[MP/204]] environment, but there may be some performance advantages in a non-MP environment.</p> | ||
<p>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 | <p> | ||
You can regard the <var>MAXOBUF</var> parameter as a user-level working set size for disk buffer pool pages. However, consider the following disadvantages of setting the value of <var>MAXOBUF</var> too high: </p> | |||
<ul> | <ul> | ||
<li> | <li>First, a too-high value can reduce the accuracy of the <var class="product">Model 204</var> [[Performance monitoring and tuning#Anticipatory writes|LRU]] algorithm for disk buffer pool pages.</li> | ||
First, a too-high value can reduce the accuracy of the <var class="product">Model 204</var> LRU algorithm for disk buffer pool pages.</li> | |||
<li> | <li>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.</li> | ||
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.</li> | |||
</ul> | </ul> | ||
<p>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.</p> | <p> | ||
Rocket Software recommends that you test for the optimal setting of <var>MAXOBUF</var> at your site by gradually increasing <var>MAXOBUF</var> until the CPU statistic compared to the work accomplished stops decreasing and starts to increase, or the DKPRF/DKPR statistics ratio stops changing significantly.</p> | |||
[[Category:System parameters]] | [[Category:System parameters]] | ||
[[Category:Parameters]] | [[Category:Parameters]] | ||
Latest revision as of 23:54, 25 August 2016
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.