For example, put Squid as a reverse proxy mode to http://www.example.com/heavyduty.php (expire set to 1 hour, need 10s to generate). When the file is just expired, large amount of clients (e.g. 10K) request for this file reached the Squid at the same time. Are there any heuristics performed by Squid to avoid forwarding all the 10K requests to the upstream?
