Performance problem description

Support personnel often receive problem reports stating that someone has a performance problem on the system and providing some data analysis. This information is insufficient to accurately determine the nature of a performance problem. The data might indicate 100 percent CPU utilization and a high run queue, but that may have nothing to do with the cause of the performance problem.

For example, a system might have users logged in from remote terminals over a network that goes over several routers. The users report that the system is slow. Data might indicate that the CPU is very heavily utilized. But the real problem could be that the characters get displayed after long delays on their terminals due to packets getting lost on the network (which could be caused by failing routers or overloaded networks). This situation might have nothing to do with the CPU utilization on the machine. If on the other hand, the complaint was that a batch job on the system was taking a long time to run, then CPU utilization or I/O bandwidth might be related.

Always obtain as much detail as possible before you attempt to collect or analyze data, by asking the following questions regarding the performance problem:

• Can the problem be demonstrated by running a specific command or reconstructing a sequence of events? (for example: ls /slow/fs or ping xxxxx). If not, describe the least complex example of the problem.
• Is the slow performance intermittent? Does it get slow, but then disappear for a while? Does it occur at certain times of the day or in relation to some specific activity?
• Is everything slow or only some things?
• What aspect is slow? For example, time to echo a character, or elapsed time to complete a transaction, or time to paint the screen?
• When did the problem start occurring? Was the situation the same ever since the system was first installed or went into production? Did anything change on the system before the problem occurred (such as adding more users or migrating additional data to the system)?
• If client/server, can the problem be demonstrated when run just locally on the server (network versus server issue)?
• If network related, how are the network segments configured (including bandwidth such as 10 Mb/sec or 9600 baud)? Are there any routers between the client and server?
• What vendor applications are running on the system, and are those applications involved in the performance issue?
• What is the impact of the performance problem on the users?