ASP.NET 4.0 compilation and application restarts?

I thought I understood this but a production problem yesterday ma开发者_开发技巧kes me question my understanding.

We do not batch compilations, instead letting ASP.NET compile pages as they're accessed. This isn't normally a problem because we do deployments on weekends and run thru tests to hit all the pages, so that everything is hunky-dory monday morning.

Except for this past weekend's deployment. We missed a bunch of pages in our testing, so they all compiled during production hours yesterday. PerfCounters for #compilations reached 100 and #application restarts was 8. But the number of running applications was also 8 and is normally just 1.

I thought that ASP.NET restarted the application after a threshold of compilations was reached, and it kept the 'old' application alive long enough for requests to complete before shutting it down for the restarted 'version' to take over. Is that so? Is it possible older restarted 'versions' of the application were still running?

What we saw, in addition to too many applications running, was a lot of memory and SQL thrashing, like all 8 apps were doing thier thing independently.

We rebooted overnight and made sure everything was compiled and everything seems fine this morning with a single app running.

is there something in 4.0 that changes this behavior?