LDKBMWNG parameter
# of pages in DKBM-ATB anticipatory write window
Summary
- Default value
- (version 7.4) The value of LDKBMWND parameter, if set; otherwise, a value of 3.
(version 7.5 and higher) A minimum of
0.5*NUMBUFG.Before the value of LDKBMWNG is adjusted or recalculated, the minimum size of NUMBUFG must first be determined by this formula:
NLRUQG * ((NSERVS + NSUBTKS) * MAXOBUF + 15)
If the current setting of NUMBUFG exceeds this value and the value is a multiple of NLRUQG, no further adjustments to NUMBUFG are made.
Following that, if a value for LDKBMWNG is specified in CCAIN and that value is greater than
0.5*NUMBUFG, the value can still be adjusted:- The final value must be an even multiple of NLRUQG
-
The final value must not be greater than NUMBUFG minus the total number of buffers that might possibly be open at any one time; that is:
NUMBUFG - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQG
- Parameter type
- System
- Where set
- On User 0's parameter line by system manager
- Related products
- All
- Introduced
- Model 204 V7.4
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 LDKBMWNG 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 Managing ATB storage with NUMBUFG for more information.