LDKBMWND parameter: Difference between revisions
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<dd>(version 7.4 and earlier) <var>[[NSERVS_parameter|NSERVS]]</var> plus 1. | <dd>(version 7.4 and earlier) <var>[[NSERVS_parameter|NSERVS]]</var> plus 1. | ||
<p>(version 7.5 and later) A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> ).</p> | <p>(version 7.5 and later) A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> ).</p> | ||
MINBUF, MAXBUF, and | The minimum size of MINBUF, MAXBUF, and NUMBUF is determined by this formula: | ||
<p class="code">NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)</p> | <p class="code">NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)</p> | ||
<p>If the current setting of NUMBUF exceeds this value and the value is a multiple of NLRUQ, no further adjustments are made.</p> | |||
Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than 0.5*NUMBUF, the value can still be adjusted: | Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than 0.5*NUMBUF, the value can still be adjusted: | ||
<ul> | <ul> | ||
Revision as of 20:47, 28 April 2016
# of pages in DKBM-BTB anticipatory write window
Summary
- Default value
- (version 7.4 and earlier) NSERVS plus 1.
(version 7.5 and later) A minimum of ( 0.5 * NUMBUF ).
The minimum size of MINBUF, MAXBUF, and NUMBUF is determined by this formula:
NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)
If the current setting of NUMBUF exceeds this value and the value is a multiple of NLRUQ, no further adjustments are made.
Following that, if a value for LDKBMWND is specified in CCAIN and that value 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
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.
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 anticipatory write windows and disk buffers.