I have a thought. The thought is that I hope I don't write a query that blows up tempdb like that in production(not trying to imply that you did)! Whats the actual mechanics of the query that baloons up the tempdb? Is it some sort of concurrent subquery thing or something? I'm always on the lookout for surprises like this, having just recently learned that Microsoft still cannot fundamentally manage storage (http://support.microsoft.com/kb/307487 "can't resize tempdb while in use" also known as failing comp sci 101), I'm sort of trying to collect info traps like this and that.