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Squid v2.x (not 3.2 as far as I can tell?) has a feature they coined Collapsed Forwarding. In a nutshell, it allows the intermediary to piggy back multiple clients on a single origin server connections. There are a few ways we could accomplish this, but they all would share the same property: this is only safe to do for cacheable objects.

Problem space and issues

The problem to solve is a form of stampeding herd: When a cached object goes stale, instead of potentially letting 100's or 1000's of requests slip through to the origin, we want to minimize this as much as possible. In a best case scenario,  a redux to 1 origin connection could be achieved. One issue here is to know if a request is cacheable (and therefore shareable). On a complete cache miss (cold cache), this can be difficult at best.

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The open read retry configurations attempt to reduce the number of concurrent requests to the origin for a given object. While an object is being fetched from the origin server, subsequent requests would wait open_read_retry_time milliseconds before checking if the object can be served from cache.

Max Open Read Retries

The maximum number of retries before going upstream to parent or origin. This is related to the previous parameter.

Example: Lets say the typical response times is 50-100ms, try setting proxy.config.http.cache.max_open_read_retries to 3 and proxy.config.http.cache.open_read_retry_time to 50

Stale While Revalidate plugin

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