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In my experience working with IIS, when a worker process is recycled, the next request to "activate" the new process has to wait whilst the process performs it's one-time startup. This wait can be particularly bad when programs are doing quite large application startups.

Is there a way through IIS to keep a minimum number of worker processes in a "ready" state, so they will serve requests immediately? I still want worker processes to be recycled, but for them not to serve requests until they're in a "ready" state, so users don't feel the startup cost.

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up vote 1 down vote accepted

In 7.5 (Windows Server 2008 R2) you can use the startMode property to ask the App Pool to boot even without a request coming in. By default, they're still demand-started (at least, so says the documentation), but adding this attribute to an applicationPool should allow it to noodle around happily, even while idle.

I agree with rfair01 though, in that it's probably a better idea not to have them recycle in the first place; this isn't always feasible, though.

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There are a couple of different things you can do:

1) Change your app pool so that it does not automatically recycle. This will keep your application ready at all times unless IIS is restarted. If you are in a shared hosting situation, this may not be practical. If you have memory issues with the application, this may not be a good approach either.

2) Use a scheduled warmup script. If app pools are on a schedule to recycle, you can create a script that will hit a page on your site to warm up the app pool. Example here. That way your application should be ready to respond quickly to requests.

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