NLRUQ parameter: Difference between revisions

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==Description==
==Description==
<p>The NLRUQ parameter reduces contention on the <var>[[Performance_monitoring_and_tuning#Multiprocessing_.28MP.2F204.29|MP]]</var> lock that protects the reuse queues. </p>
<p>
<p>This MP lock is a primary source of MP overhead. Setting this parameter to greater than 1 has no benefit in a non-MP run. In fact, in all cases a setting of greater than 1 might result in a slight increase in disk I/O, due to a loss in precision in the least-recently used algorithm for managing the disk buffer pool. With NLRUQ greater than 1, it would be possible for a page to be stolen from the buffer pool before one that was less recently used.</p>
The <var>NLRUQ</var> parameter reduces contention on the <var>[[Performance monitoring and tuning#Multiprocessing (MP/204)|MP]]</var> lock that protects the reuse queues. </p>
<p>NLRUQ=1 preserves the single reuse queue model used in releases of <var class="product">Model&nbsp;204</var> before V6R1.0. </p>
<p>
This MP lock is a primary source of MP overhead. Setting this parameter to greater than 1 has no benefit in a non-MP run. In fact, in all cases a setting of greater than 1 might result in a slight increase in disk I/O, due to a loss in precision in the least-recently used algorithm for managing the disk buffer pool. With NLRUQ greater than 1, it would be possible for a page to be stolen from the buffer pool before one that was less recently used.</p>
<p>
NLRUQ=1 preserves the single reuse queue model used in releases of <var class="product">Model&nbsp;204</var> before V6R1.0. </p>
<p>In the following formula NLRUQ is used as a multiplier to determine the minimum number of disk buffers used in an Online. </p>
<p>In the following formula NLRUQ is used as a multiplier to determine the minimum number of disk buffers used in an Online. </p>
<p class="code"><var>[[MINBUF_parameter|MINUF]]</var> >= NLRUQ * ((<var>[[NSERVS_parameter|NSERVS]]</var> + <var>[[NSUBTKS_parameter|NSUBTKS]]</var>) * <var>[[MAXOBUF_parameter|MAXOBUF]]</var> + 15)
<p class="code"><var>[[MINBUF parameter|MINBUF]]</var> >= NLRUQ * ((<var>[[NSERVS parameter|NSERVS]]</var> + <var>[[NSUBTKS parameter|NSUBTKS]]</var>) * <var>[[MAXOBUF parameter|MAXOBUF]]</var> + 15)
</p>
</p>
<p>A reasonable guess for a proper NLRUQ would be adding two for each MP subtask so that a setting of <var>[[NMPSUBS_parameter|NMPSUBS]]</var>=1 would suggest NLRUQ=3 and NMPSUBS=7 would suggest NLRUQ=15. </p>
<p>
<p>If NLRUQ is set greater than 1, then the values of <var>[[LDKBMWND_parameter|LDKBMWND]]</var>, <var>[[MAXBUF_parameter|MAXBUF]]</var>, and MINBUF are all rounded up to a multiple of NLRUQ. The maximum setting for NLRUQ is 255. </p>
A reasonable guess for a proper NLRUQ would be adding two for each MP subtask so that a setting of <code>[[NMPSUBS parameter|NMPSUBS]]=1</code> would suggest <code>NLRUQ=3</code>, and <code>NMPSUBS=7</code> would suggest <code>NLRUQ=15</code>. </p>
<p>A high conflict count for LRU queue locks that would appear in <var>[[MONITOR_MPLOCK_parameter|MONITOR MPLOCK]]</var> command output indicates that you should increase NLRUQ and <var>[[NLRUQG_parameter|NLRUQG]]</var>.</p>
<p>
If NLRUQ is set greater than 1, the values of <var>[[LDKBMWND parameter|LDKBMWND]]</var>, <var>[[MAXBUF parameter|MAXBUF]]</var>, and MINBUF are all rounded up to a multiple of NLRUQ. The maximum setting for NLRUQ is 255. </p>
<p>
A high conflict count for LRU queue locks that would appear in <var>[[MONITOR MPLOCK command|MONITOR MPLOCK]]</var> command output indicates that you should increase NLRUQ and <var>[[NLRUQG_parameter|NLRUQG]]</var>.</p>
 
[[Category:System parameters]]
[[Category:System parameters]]
[[Category:Parameters]]
[[Category:Parameters]]

Revision as of 16:35, 1 September 2015

# of DKBM LRU queues

Summary

Default value
1, also the minimum
Parameter type
System
Where set
Not resettable
Related products
All
Introduced
Model 204 V6.1

Description

The NLRUQ parameter reduces contention on the MP lock that protects the reuse queues.

This MP lock is a primary source of MP overhead. Setting this parameter to greater than 1 has no benefit in a non-MP run. In fact, in all cases a setting of greater than 1 might result in a slight increase in disk I/O, due to a loss in precision in the least-recently used algorithm for managing the disk buffer pool. With NLRUQ greater than 1, it would be possible for a page to be stolen from the buffer pool before one that was less recently used.

NLRUQ=1 preserves the single reuse queue model used in releases of Model 204 before V6R1.0.

In the following formula NLRUQ is used as a multiplier to determine the minimum number of disk buffers used in an Online.

MINBUF >= NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)

A reasonable guess for a proper NLRUQ would be adding two for each MP subtask so that a setting of NMPSUBS=1 would suggest NLRUQ=3, and NMPSUBS=7 would suggest NLRUQ=15.

If NLRUQ is set greater than 1, the values of LDKBMWND, MAXBUF, and MINBUF are all rounded up to a multiple of NLRUQ. The maximum setting for NLRUQ is 255.

A high conflict count for LRU queue locks that would appear in MONITOR MPLOCK command output indicates that you should increase NLRUQ and NLRUQG.