Rational® ClearCase® hosts
that use dynamic views can benefit from MVFS cache tuning. Default MVFS cache
sizes scale automatically based on host memory and are appropriate for a wide
range of client needs, but you might want to change default MVFS cache sizes
to improve performance in specific cases.
All cache tuning requires an intelligent trade-off between specific performance
benefits that might result from larger caches and the potential for degraded
application performance due to the dedication of more physical memory to caches.
Cache tuning can help reallocate the MVFS’s use of available memory in ways
that reflect a particular host’s patterns of use, but it cannot compensate
for inadequate physical memory.
To examine MVFS cache sizes and utilization, use the
cleartool getcache –mvfs command.
You can change MVFS cache size in two ways:
- The easiest (and best) way is to adjust the MVFS scaling factor, an integer
value from which most other MVFS cache sizes are derived. Use cleartool setcache
–mvfs –persistent –scalefactor to adjust the scaling factor on
any supported operating system (you must use the –persistent option
when setting the scaling factor). On Windows®, you can also use the ClearCase program in Control
Panel. The MVFS Performance page allows you to set
the scaling factor and several other cache sizes.
- You can also adjust selected values for individual caches by using setcache
–mvfs or the MVFS Performance page of the ClearCase program in Control
Panel. This method provides finer control, although it requires extensive
analysis and testing, and can actually degrade performance if not done correctly.
Do not use this method unless there are unusual circumstances that make values
derived from the scaling factor unsuitable.
Note: Changes you make with setcache –mvfs are normally
temporary and revert to their default values when the MVFS is restarted. setcache includes
a –persistent option that enables changes you
make in the scaling factor or individual caches to persist across restarts.
Changes made on the MVFS Performance page are always
persistent.