PDT collects configuration, availability, workload, and performance data on a daily basis. This data is maintained in a historical record. Approximately one month's data is kept in this way. Also on a daily basis, PDT generates a diagnostic report, which is mailed to the adm user.
In addition to mailing the report, PDT stores a copy in the /var/perf/tmp/PDT_REPORT file. Before the new report is written, the previous report is renamed /var/perf/tmp/PDT_REPORT.last.
While many common system performance problems are of a specific nature (a system might have too little memory), PDT also attempts to apply some general concepts of well-performing systems to its search for problems. Some of these concepts, together with examples of their application to the operating system, are as follows:
In general, if there are several resources of the same type, then a balanced use of those resources produces better performance.
Resources have limits to their use. Trends attempting to exceed those limits should be detected and reported.
Trends can indicate a change in the nature of the workload, as well as increases in the amount of resource used:
Hardware or software errors often produce performance problems:
New workloads or processes that start to consume resources may be the first sign of a problem.
There are many parameters in a system, and they must be set correctly.
PDT normally uses less than 30 seconds of CPU time. Daily data collection takes several elapsed minutes.