Configuring Multiple Worker Processes for Application Pools

Multiple worker processes running in their own context can share responsibility for handling requests for an application pool. This configuration is also referred to as a Web garden. When you define a Web garden, each new request is assigned to a worker process according to a round-robin scheme. Round-robin is a load balancing technique used to spread the workload among the worker processes that are available.

Note

It’s important to note that worker processes aren’t started automatically and don’t use resources until they’re needed. Rather, they’re started as necessary to meet the demand based on incoming requests. For example, if you configure a maximum of five worker processes for an application pool, there may be at any given time from zero to five worker processes running in support of applications placed in that application pool.

If a single application is placed in an application pool serviced by multiple worker processes, any and all worker processes available will handle requests queued for the application. This is a multiple worker process–single application configuration, and it’s best used when you want to improve the application’s request handling performance and reduce any possible contention for resources with other applications. In this case the application might have heavy usage during peak periods and moderate-to-heavy usage during other times, or individuals using the application might have specific performance expectations that must be met if possible.

If multiple applications are placed in an application pool serviced by multiple worker processes, any and all worker processes available handle requests queued for any applicable application. This is a multiple worker process–multiple application configuration, and it’s best used when you want to improve request handling performance and reduce resource contention for multiple applications but don’t want to dedicate resources to any single application. In this case the various applications in the application pool might have different peak usage periods or might have varying resource needs.

To configure multiple worker processes for an application pool, follow these steps:

1. In the IIS snap-in, expand Application Pools, right-click the application pool that you want to configure, and then select Properties.

2. On the Performance tab, use the Maximum Number Of Worker Processes field in the Web Garden frame to specify the number of worker processes that the application pool should use.

3. Click OK.

   Real World

   When you assign multiple worker processes to a busy application pool, keep in mind that each worker process uses server resources when it’s started and might affect the performance of applications in other application pools. Adding worker processes won’t resolve latency issues due to network communications or bandwidth, and it can reduce the time it takes to process requests only if those requests were queued and waiting and not being actively processed. A poorly engineered application will still respond poorly, and, at some point, you’d need to look at optimizing the application code for efficiency and timeliness.