NLRUQ parameter: Difference between revisions
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==Description== | ==Description== | ||
<p> | <p> | ||
The <var>NLRUQ</var> parameter reduces contention on the | The <var>NLRUQ</var> parameter reduces contention on the [[Performance monitoring and tuning#Multiprocessing (MP/204)|MP]] 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> | 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 <var>NLRUQ</var> 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> | <p> | ||
NLRUQ=1 preserves the single reuse queue model used in releases of <var class="product">Model 204</var> before V6R1.0. </p> | <code>NLRUQ=1</code> preserves the single reuse queue model used in releases of <var class="product">Model 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> | ||
In the following formula, <var>NLRUQ</var> is used as a multiplier to determine the minimum number of disk buffers used in an Online: </p> | |||
<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 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> | <p> | ||
A reasonable guess for a proper NLRUQ | A reasonable guess for a proper <var>NLRUQ</var> value adds two for each MP subtask, so a setting of <code>[[NMPSUBS parameter|NMPSUBS]]=1</code> suggests <code>NLRUQ=3</code>, and <code>NMPSUBS=7</code> suggests <code>NLRUQ=15</code>. </p> | ||
<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> | If <var>NLRUQ</var> is set greater than 1, the values of <var>[[LDKBMWND parameter|LDKBMWND]]</var>, <var>[[MAXBUF parameter|MAXBUF]]</var>, and <var>MINBUF</var> are all rounded up to a multiple of <var>NLRUQ</var>. The maximum setting for <var>NLRUQ</var> is 255. </p> | ||
<p> | <p> | ||
If you see a high conflict count for LRU queue locks in <var>[[MONITOR MPLOCK command|MONITOR MPLOCK]]</var> command output, increase <var>NLRUQ</var> and <var>[[NLRUQG_parameter|NLRUQG]]</var>.</p> | |||
[[Category:System parameters]] | [[Category:System parameters]] | ||
[[Category:Parameters]] | [[Category:Parameters]] | ||
Revision as of 21:55, 18 August 2016
# 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 value adds two for each MP subtask, so a setting of NMPSUBS=1 suggests NLRUQ=3, and NMPSUBS=7 suggests 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.
If you see a high conflict count for LRU queue locks in MONITOR MPLOCK command output, increase NLRUQ and NLRUQG.