LDKBMWND parameter: Difference between revisions

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<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>
<p>
If <var>[[NLRUQ parameter|NLRUQ]]</var> is set greater than 1, then the value of <var>LDKBMWND</var> is rounded up to a multiple of <var>NLRUQ</var>. <var>LDKBMWND</var> has a minimum size of one (1). </p>
<p>
<p>
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>
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>

Revision as of 19:19, 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.

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.