Why you want to use the performance advisors
The advisors analyze the Performance Monitoring Infrastructure (PMI) data of WAS 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 WebSphere Application Server. The advisors provide a variety of advice on the following appserver 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
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 that are 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.
Use another example with pools in the appserver, 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 appserver 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 your application requires more memory than is available, the diagnostic adviser tells you to increase the size or the heap for appserver.
Related tasks
Obtaining advice from the advisors