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I was working on an issue with appdomain restarts caused by page re-compilations because aspx pages were created and modified from the code. You can get lifetime event information such as shutdown reasons, compilation information etc. in the eventlog by enabling Application Life Time Events in your web.config (See this post for more info about this and application restarts in general)
We were seeing a lot of the following messages
EventID: 1305 Event code: 1001 Event message: Application is starting
EventID: 1305 Event code: 1002 Event message: Application is shutting down. Reason: Maximum number of recompilations was reached
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