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AIX Versions 3.2 and 4 Performance Tuning Guide

Inference from the Kind of Performance Problem Reported

When a performance problem is reported, the kind of performance problem will often help the performance analyst to narrow the list of possible culprits.

This topic includes the following major sections:

If everything that uses a particular device or service slows down at times, refer to the topic that covers that device or service:

A Particular Program Runs Slowly

This may seem to be the trivial case, but there are still questions to be asked:

Everything Runs Slowly at a Particular Time of Day

Most people have experienced the rush-hour slowdown that occurs because a large number of people in the organization habitually use the system at one or more particular times each day. This phenomenon is not always simply due to a concentration of load. Sometimes it is an indication of an imbalance that is (at present) only a problem when the load is high. There are also other sources of periodicity in the system that should be considered.

If you find that the problem stems from conflict between foreground activity and long-running, CPU-intensive programs that are, or should be, run in the background, you should consider using schedtune -r -d to give the foreground higher priority. See "Tuning the Process-Priority-Value Calculation with schedtune".

Everything Runs Slowly at Unpredictable Times

The best tool for this situation is an overload detector, such as xmperf's filtd program (a component of PTX). filtd can be set up to execute shell scripts or collect specific information when a particular condition is detected. You can construct a similar, but more specialized, mechanism using shell scripts containing vmstat, netstat, and ps.

If the problem is local to a single system in a distributed environment, there is probably a pathological program at work, or perhaps two that intersect randomly.

Everything an Individual User Runs Is Slow

Sometimes a system seems to "pick on" an individual.

A Number of LAN-Connected Systems Slow Down Simultaneously

There are some common problems that arise in the transition from independent systems to distributed systems. They usually result from the need to get a new configuration running as soon as possible, or from a lack of awareness of the cost of certain functions. In addition to tuning the LAN configuration in terms of MTUs and mbufs (see the Monitoring and Tuning Communications I/O chapter), we should look for LAN-specific pathologies or nonoptimal situations that may have evolved through a sequence of individually reasonable decisions.

Everything That Uses a Particular Service or Device Slows Down at Times

Make sure you have followed the configuration recommendations in the appropriate subsystem manual and/or the recommendations in the appropriate "Monitoring and Tuning" chapter of this book.

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