As far as threadedness goes, I believe activerecord can be used thread 
safely (backgroundrb used to do that before they switched to 
process-based workers instead of thread-based workers).

If you are using something like fastcgi or mongrel, then each instance 
of those has its own ruby interpreter: changes made in one of those 
don't change what's happening in another process.

So if I add a method to a class, change a class variable etc... that 
will only affect the mongrel/fastcgi process that that statement 
executed in. Subsequent requests to the same mongrel will see that 
change, but those that get handled by a different mongrel won't see the 
change.

Fred

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