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We have the IIS Crash/Hang agent installed on the production IIS servers. It seems to record quite a lot of start/stop events. Do these imply that something is really happening? if so, what other events should I be looking for to correlate? I don't see anything that looks significant except possibly for an ASP .NET event that's pretty much "invalid session id"

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How about giving us some details about the events that are being logged. – joeqwerty May 26 '11 at 16:55
Agreed. Also, set LogEventOnRecycle=255 and see if it correlates with App Pool shutdowns (recycling). – TristanK May 26 '11 at 22:22

This is probably just normal recycling behaviour.

By default, IIS App Pools will recycle:

  • every 29 hours or
  • every time they reach 20 minutes without activity

They're started on demand, i.e. when a request arrives.

Setting LogEventOnRecycle to 255 - everything on - will help you correlate Start/Stop events with app pool activity.

(IIS6: ; IIS 7 exposes the possible flags through advanced App Pool properties, Recycling)

You haven't specified anything except "invalid session ID" - what are you looking for?

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