Tuning Performance (IIS 6.0)

When IIS is running in worker process isolation mode, you can tune the performance of your applications to conserve CPU and memory resources, and to add worker processes to application pools that need them. By setting the application pool properties for idle time-out, you can optimize the time that worker processes remain idle for each application pool, removing them from memory. Another way to conserve memory is to shorten the request queue length limit property for the worker processes in each application pool.

You can increase the number of worker processes that are available to an application pool by configuring a Web garden, which is an application pool that is served by more than one worker process. When a worker process is engaged, another worker process can continue to process requests, enhancing server performance. Finally, on a computer with more than one CPU, you can establish affinity between worker processes and specific CPUs, ensuring that applications are tied to processors in accordance with your priorities.

Managing Isolation and Performance

To help achieve high levels of application availability, you can assign fewer applications to each application pool, as low as one application per application pool. This increases isolation, protecting applications from each other. However, configuring fewer applications per application pool increases the total number of application pools. This results in greater CPU and memory usage, degrading server performance, and resulting in reduced request-processing throughput.

The performance impact of increasing the number of application pools on a computer varies based on the number of application pools that are running worker processes. If there are a large number application pools, but few worker processes are running, the impact is relatively small; if there are a large number application pools and many worker processes are running, worker processes can impact each other as they use up memory and CPU capacity, thereby negatively impacting performance.

The degree to which increasing application isolation causes performance degradation can only be determined by testing. You can test for the optimum level of isolation by doing the following:


Set the highest level of isolation that your configuration can support, and test with all application pools running simultaneously. Assess the results after using Performance Monitor to record requests processed per second, CPU usage, and memory usage. If performance is satisfactory, the test is complete; if performance is not satisfactory, proceed to Step 2.


If the results in Step 1 are unsatisfactory, reduce the isolation level by reducing the number of application pools, and then run the test again.


Continue Step 2 until you achieve satisfactory performance. In addition to reducing the number of application pools, you might need to remove applications from the server.

For information about isolating applications, see Isolate Applications in Worker Process Isolation Mode. For information about assigning applications to application pools by using a command-line procedure or scripts, see the AppPoolId Metabase Property.

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