Why we want to use the performance advisors

The advisors analyze the Performance Monitoring Infrastructure (PMI) data of WebSphere Application Server using general performance principles, best practices, and WAS-specific rules for tuning. The advisors that are based on this information provide advice on how to set some of the configuration parameters to better tune WAS.

The advisors provide a variety of advice on the following application server resources:

• Object Request Broker service thread pools
• Web container thread pools
• Connection pool size
• Persisted session size and time
• Data source statement cache size
• Session cache size
• Dynamic cache size
• Java virtual machine heap size
• DB2 Performance Configuration wizard
• Connection use violations

For example, consider the data source statement cache. It optimizes the processing of prepared statements and callable statements by caching those statements that are not used in an active connection. (Both statements are SQL statements that essentially run repeatable tasks without the costs of repeated compilation.) If the cache is full, an old entry in the cache is discarded to make room for the new one. The best performance is generally obtained when the cache is large enough to hold all of the statements used in the application. The PMI counter, prepared statement cache discards, indicates the number of statements that are discarded from the cache. The performance advisors check this counter and provide recommendations to minimize the cache discards.

Another example is thread or connection pooling. The idea behind pooling is to use an existing thread or connection from the pool instead of creating a new instance for each request. Because each thread or connection in the pool consumes memory and increases the context-switching cost, the pool size is an important configuration parameter. A pool that is too large can hurt performance as much as a pool that is too small. The performance advisors use PMI information about current pool usage, minimum or maximum pool size, and the application server CPU utilization to recommend efficient values for the pool sizes.

The advisors can also issue diagnostic advice to help in problem determination and health monitoring. For example, if the application requires more memory than is available, the diagnostic adviser tells you to increase the size or the heap for application server.

Subtopics

• Performance advisor types and purposes
  Two performance advisors are available: the Performance and Diagnostic Advisor and the performance advisor in Tivoli Performance Viewer.

Obtain advice from the advisors