LDKBMWND parameter: Difference between revisions
m (add link) |
|||
| (17 intermediate revisions by 5 users not shown) | |||
| Line 1: | Line 1: | ||
{{Template:LDKBMWND parameter subtitle}} | |||
==Summary== | ==Summary== | ||
<dl> | <dl> | ||
<dt>Default value | <dt>Default value | ||
<dd>NSERVS plus 1 | <dd>V7.4 and earlier: <var>[[NSERVS_parameter|NSERVS]]</var> plus 1 | ||
<p> | |||
V7.5 and later: A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> )</p> | |||
<p> | |||
V7.7 and later: If <var>[[NUMBUFG parameter|NUMBUFG]]</var> is greater than 0, <var>LDKBMWND</var> is ignored </p> | |||
Before the value of <var>LDKBMWND</var> is adjusted or recalculated, the minimum size of <var>NUMBUF</var> must first be determined by this formula: | |||
<p class="code">NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)</p> | |||
<p> | |||
If the current value of <var>NUMBUF</var> exceeds this value and is a multiple of <var>[[NLRUQ parameter|NLRUQ]]</var>, no further adjustments to <var>NUMBUF</var> are made. | |||
</p> | |||
Following that, if a value for <var>LDKBMWND</var> is specified in CCAIN and is greater than <code>0.5*NUMBUF</code>, the value can still be adjusted: | |||
<ul> | |||
<li>The final value must be an even multiple of <var>NLRUQ</var></li> | |||
<li>The final value must <i>not</i> be greater than <var>NUMBUF</var> minus the total number of buffers that might possibly be open at any one time: | |||
<p class="code">NUMBUF - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQ</p> </li> | |||
</ul> | |||
<dt>Parameter type | <dt>Parameter type | ||
<dd>System | <dd>System | ||
| Line 12: | Line 29: | ||
<dd><var class="product">Model 204 V6.1</var> or earlier | <dd><var class="product">Model 204 V6.1</var> or earlier | ||
</dl> | </dl> | ||
==Description== | ==Description== | ||
<p> | <p> | ||
<p>When an anticipatory write for a modified buffer completes, the buffer is immediately reusable. </p> | <var>LDKBMWND</var> specifies an anticipatory write window that starts writes for any modified below-the-bar buffers that enter the window.</p> | ||
<p> | <p> | ||
When an anticipatory write for a modified buffer completes, the buffer is immediately reusable. </p> | |||
< | <p> | ||
[[Category:System | High values of <var>LDKBMWND</var> might unnecessarily increase the number of writes done (measured by the DKWR statistic). Low values might cause excessive waiting for buffers (measured by the DKSWAIT statistic).</p> | ||
==See also== | |||
<ul> | |||
<li>[[Performance monitoring and tuning#Disk buffer monitor statistics and parameters|Disk buffer monitor statistics and parameters]] and [[Defining the runtime environment (CCAIN)#Disk buffers and Model 204 storage|Disk buffers and Model 204 storage]], for more information about anticipatory write windows and disk buffers </li> | |||
<li><var>[[LDKBMWNG parameter|LDKBMWNG]]</var> </li> | |||
</ul> | |||
[[Category:System parameters]] | |||
[[Category:Parameters]] | [[Category:Parameters]] | ||
Latest revision as of 21:18, 22 September 2016
# of pages in DKBM-BTB anticipatory write window
Summary
- Default value
- V7.4 and earlier: NSERVS plus 1
V7.5 and later: A minimum of ( 0.5 * NUMBUF )
V7.7 and later: If NUMBUFG is greater than 0, LDKBMWND is ignored
Before the value of LDKBMWND is adjusted or recalculated, the minimum size of NUMBUF must first be determined by this formula:
NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)
If the current value of NUMBUF exceeds this value and is a multiple of NLRUQ, no further adjustments to NUMBUF are made.
Following that, if a value for LDKBMWND is specified in CCAIN and is greater than
0.5*NUMBUF, the value can still be adjusted:- The final value must be an even multiple of NLRUQ
- The final value must not be greater than NUMBUF minus the total number of buffers that might possibly be open at any one time:
NUMBUF - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQ
- Parameter type
- System
- Where set
- On User 0's parameter line by system manager
- Related products
- All
- Introduced
- Model 204 V6.1 or earlier
Description
LDKBMWND specifies an anticipatory write window that starts writes for any modified below-the-bar buffers that enter the window.
When an anticipatory write for a modified buffer completes, the buffer is immediately reusable.
High values of LDKBMWND might unnecessarily increase the number of writes done (measured by the DKWR statistic). Low values might cause excessive waiting for buffers (measured by the DKSWAIT statistic).
See also
- Disk buffer monitor statistics and parameters and Disk buffers and Model 204 storage, for more information about anticipatory write windows and disk buffers
- LDKBMWNG