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How to Improve Performance 5-19
How Is Tuning Done?
How Is Tuning Done?
If the cached-read percentage is lower than 95 percent, you might be able to
improve performance by lowering the values of LRU_MAX_DIRTY and
LRU_MIN_DIRTY to increase the number of free and/or unmodified pages
that are available in the shared-memory LRU queues.
If the cached-write percentage is lower than 82 percent, you might be able to
improve performance by increasing the LRU_MAX_DIRTY and
LRU_MIN_DIRTY values. This increases the number of modified buffers that
are able to accumulate in the MLRU queue and increases the likelihood that
pages will be reused before they are written to disk.
To change the value of either of these parameters, edit the configuration file
using an operating system editor.
The optimal value of CLEANERS depends on your specific hardware config-
uration. The maximum value of CLEANERS is 32. The minimum value is 0.
When CLEANERS is set to 0, the tbinit daemon assumes all responsibility for
page cleaning.
You might want to configure a page cleaner for each separate physical device.
However, if more than one disk shares a controller channel, you might find
that more than three page cleaners per controller overburdens the controller.
In most cases, the additional cleaners do not improve performance unless
you separate successive chunks from a blobspace or dbspace on the disk.
Ideally, you should try to assign successive chunks to separate disk devices.
(Refer to page 1-43 for more details about disk layout. Refer to page 3-115 for
more details about how to change the number of page cleaners.)
The default value of LRUS is the larger of USERS/2 or 8, where USERS is the
specified configuration file parameter. The minimum value of LRUS is 3 and
the maximum value is 8. The optimal value of LRUS depends on your specific
hardware configuration. Your best guide for selecting a value for LRUS is to
experiment with different values and monitor the performance benefits. You
might find that a larger value increases performance on machines with more
than two CPUs. To change the value of LRUS, edit the configuration file using
an operating system editor.