LDKBMWND parameter: Difference between revisions
(Added a detailed description on how LDKBMWND is calculated) |
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<dl> | <dl> | ||
<dt>Default value | <dt>Default value | ||
<dd><var>[[NSERVS_parameter|NSERVS]]</var> plus 1 for | <dd><var>[[NSERVS_parameter|NSERVS]]</var> plus 1 -- for version 7.4 and earlier. | ||
<p>A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> ) -- for version 7.5 and later.</p> | |||
NUMBUF will first be adjusted (rounded up) to be an even multiple of <var>[[NLRUQ parameter|NLRUQ]]</var>. Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than .5*NUMBUF, the value can still be adjusted: | |||
<ul> | |||
<li>The final value must be an even multiple of NLRUQ</li> | <li>The final value must be an even multiple of NLRUQ</li> | ||
<li>The final value must not be greater than NUMBUF minus the total number of buffers that might possibly be open at any one time: | <li>The final value must not be greater than NUMBUF minus the total number of buffers that might possibly be open at any one time: that is, <br />NUMBUF - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQ </li> | ||
</ul> | |||
<dt>Parameter type | <dt>Parameter type | ||
<dd>System | <dd>System | ||
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==Description== | ==Description== | ||
<p> | <p> | ||
An anticipatory write window that starts writes for any modified buffers that enter the window</p> | An anticipatory write window that starts writes for any modified buffers that enter the window.</p> | ||
<p> | <p> | ||
When an anticipatory write for a modified buffer completes, the buffer is immediately reusable. </p> | When an anticipatory write for a modified buffer completes, the buffer is immediately reusable. </p> | ||
Revision as of 16:30, 28 April 2016
# of pages in DKBM-BTB anticipatory write window
Summary
- Default value
- NSERVS plus 1 -- for version 7.4 and earlier.
A minimum of ( 0.5 * NUMBUF ) -- for version 7.5 and later.
NUMBUF will first be adjusted (rounded up) to be an even multiple of NLRUQ. Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than .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: that is,
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
An anticipatory write window that starts writes for any modified buffers that enter the window.
When an anticipatory write for a modified buffer completes, the buffer is immediately reusable.
If NLRUQ is set greater than 1, then the value of LDKBMWND is rounded up to a multiple of NLRUQ. LDKBMWND has a minimum size of one (1).
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).
Refer to Disk buffer monitor statistics and parameters and Disk buffers and Model 204 storage for more information about disk buffers.