Investigating performance problems

Performance can be adversely affected by:

• Buffer pools that are an incorrect size

• Lack of real storage

• I/O contention for page sets or logs

• Log buffer thresholds that are set incorrectly

• Incorrect setting of the number of log buffers

• Large messages

• Units of recovery that last a long time, incorporating many messages for each syncpoint

• Messages that remain on a queue for a long time

• RACF auditing

• Unnecessary security checks

• Inefficient program design

When you analyze performance data, always start by looking at the overall system before you decide that you have a specific WebSphere MQ problem. Remember that almost all symptoms of reduced performance are magnified when there is contention. For example, if there is contention for DASD, transaction response times can increase. Also, the more transactions there are in the system, the greater the processor overhead and greater the demand for both virtual and real storage.

In such situations, the system shows heavy use of all its resources. However, the system is actually experiencing normal system stress, and this might be hiding the cause of a performance reduction. To find the cause of such a loss of performance, consider all items that might be affecting your active tasks.