What is worker process recycling....?

Question

1. I would like to know what is exactly worker process recycling?
2. What exactly it does at the time of worker process recycling?
3. Worker process resides in application pool and can be configured through application pool?
4. Is that application pool is responsible to recycle worker process? or IIS is responsible to recycle it?
5. What happens at the time recycling worker process?
6. What are the impact of not forcing it to recycle?

Redraft

Answer 1

IIS Worker Process Recycling is the process whereby IIS kills of the child processes that it spawns to handle incoming requests and starts clean copies of them.

The first time IIS gets a request for a web application in a given application pool, it spawns a worker process to actually do the work. This process does things like maintaining the session state and static data from your ASP.NET code, ISAPI handlers, etc. Over time, problems could arise in the processing (memory leaks in the application code, undisposed resources, etc.) that IIS wants to clean up without having to shut down the server. So it will periodically tell the worker process to die off, and spawn a new one.

When the recycle period comes around, IIS stops sending new service requests to the dying process and allows it to finish whatever it's doing normally. It will spawn a new, replacement process in advance and start sending new requests to that one while the old one finishes up. Once there's nothing left for the old process to do, it terminates normally.

Worker processes are isolated to a given application pool, because that's how IIS accomplishes process isolation. (This is why, for example, you can mix .NET Framework versions on a single server -- each app pool gets its own loaded Framework libraries separate from the others.) The app pool determines other things about the worker processes, including their credentials and how long the process stays around before being shut down.

There's really not a good reason to turn off recycling, but if everything is working properly it shouldn't hurt anything. The problems arise if you run code within the worker process that misbehaves; over time even tiny memory or resource leaks build up and you have to shut down application pool down to clean them up. With overlapped recycling, IIS takes care of that for you with no disruption in service.

Inject

+1: To add a little more, you might start hurting performance if you turn recycling off all together. After a long time, the heap will become fragmented, even if you are sure your application is not leaking memory at all. – Motherwell

@vcsjones, thanks for adding few points to understand problems associated if not recycled workerprocess – Redraft

Answer 2

Worker process recycling just means the restart of the asp .net worker process (aspnet_wp.exe) . It's done due to various reasons. The following article describes things quite decently. http://technet.microsoft.com/en-us/library/cc759005(WS.10).aspx

Please go through it.

Honeywell

is it restarting aspnet_wp.exe or w3wp.exe? – Redraft

Not quite, there are a few exceptions to that. It's tied more to the IIS version than whether it is Server/Client. In IIS 6.0+ it is w3wp.exe, less than 6 uses aspnet_wp. Windows XP 64-bit, which isn't a server, uses IIS6 so you still get App Pools and w3wp. Windows Server 2000, which is is a server, uses aspnet_wp since IIS doesn't support App Pools. – Motherwell

@Motherwell you are right :). Just deleted my above comment to avoid confusion. The difference is IIS6 has w3wp.exe and lower versions of IIS its aspnet_wp.exe – Honeywell

Answer 3

Scenarios vary, but just to keep in mind: If your web app does initial in-memory caching of db information (let's say huge initial caching), the first request to the newly spawned apppool will take long to complete.

Lipcombe