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Once it appears that the hypothesis is correct, you can make adjustments to the system. It is vital that you record the parameters that the system had initially, and the changes that you make at each stage. Make all adjustments in small steps to ensure that they have the desired effect. After each adjustment, reassess the system's performance using the same commands that you used to measure its initial performance.
You should normally adjust kernel parameters one at a time so that you can uniquely identify the effect that an adjustment has. If you adjust several things at once, the interaction between them may mask the effect of the change. Some parameters, however, are intended to be adjusted in groups rather than singly. In such a case, always adjust the minimum number of parameters, and always adjust the same set of parameters. For example, NBUF and NHBUF form such a group of parameters.
If your adjustment degrades system performance, retrace your steps to a point where it was at its peak before trying to adjust any other parameters on the system. If your performance goals are not met, you must further evaluate and tune the system. This may mean making changes similar to the ones that you have already made, or you may need to consider improving the performance of other subsystems.
If you have attained your performance goals, then you can check the system against the lists of desired attributes of well-tuned multiuser or database server systems given in ``Quick system tuning reference''. You should continue to monitor system performance as part of routine system administration to ensure that you recognize and treat any possible future degradation in performance at an early stage.
If you adopt the habit of monitoring performance on a regular basis,
you should be able to spot correlations
between the numbers recorded and changing demands on the system.
Bursts of high system activity during the day,
on a particular day of the week, month, or quarter
almost certainly reflect the pattern of activity by users,
either logged on or running batch jobs.
It is up to you to decide how to manage this.
You can choose to tune or upgrade the system
to cope with peak demand,
to reschedule jobs
to make use of periods of normally low activity, or both.