# of DKBM LRU queues
- Default value
- 1 (also the minimum)
- Parameter type
- Where set
- Not resettable
- Related products
- Model 204 V6.1
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 NLRUQ greater than 1 has no benefit in a non-MP run. In fact, in all cases, a setting greater than 1 might result in a slight increase in disk I/O, owing to a loss in precision in the least-recently-used algorithm for managing the below the bar (BTB) disk buffer pool. With NLRUQ greater than 1, it would be possible for a page to be stolen from the BTB buffer pool before one that was less recently used.
Note: As of version 7.7 of Model 204, whether BTB buffers are used at all depends entirely on the setting of NUMBUFG, which activates buffer storage above the bar.
- If NUMBUFG is greater than 0, all buffer pool buffers are forced above the bar — no buffers are below the bar. The MINBUF and NUMBUF parameters are forced to 0, and the other parameters that affect BTB storage (MAXBUF, SPCORE, LDKBMWND, and NLRUQ) are ignored.
- If NUMBUFG is set to 0, all buffers are below the bar, and the settings of the BTB-related parameters are respected and calculated as in pre-7.7 versions.
If BTB buffers are used
When BTB buffers are being used (that is, NUMBUFG is 0 under version 7.7 or higher, or NUMBUFG is any value under Model 204 prior to 7.7):
NLRUQ=1preserves the single reuse queue model used in releases of Model 204 before V6R1.0.
- NLRUQ is used as a multiplier to determine the minimum number of BTB disk buffers used in an Online:
- A reasonable guess for a proper NLRUQ value adds two for each MP subtask, so a setting of
- 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 a MONITOR MPLOCK command output reveals a high conflict count for LRU queue locks, increase NLRUQ and NLRUQG.