LDKBMWND parameter

# of pages in DKBM-BTB anticipatory write window

Summary

Default value

NSERVS plus 1 for releases up to and including V7.4. From V7.5 onwards, the default has been changed to a minimum of ( 0.5 * NUMBUF ). 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 may 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: i.e 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.