A brand new Rails/Merb app you put together over a weekend, a pack of Mongrels, a reverse proxy (like Nginx), and you're up and running. Well, almost, what about that one request that tends to run forever, often forcing the user to double check their internet connection? Response time is king, and you always want to make sure that your site feel snappy to the user. Did you know that Flickr optimizes all of their pages to render in sub 250ms?
When you're fighting with response times, the worst thing you can possibly do is queue up another request behind an already long running process. Not only does the first request take forever, but everyone else must wait in line for it to finish as well! To mitigate the problem HAProxy goes beyond a simple round-robin scheduler, and implements a very handy feature: intelligent request queuing!
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更多http://www.igvita.com/2008/05/13/load-balancing-qos-with-haproxy/
