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Squid v2.x (not 3.x 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.

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There is a plugin that implements Stale While Revalidate, which is documented in RFC 5861. With this plugin, you are allowed to serve objects stale in cache, while one request goes to origin to fetch the new version. Combined with read-while-write, and the fuzzy logic feature, this is a good alternative to the Open-Retry feature. The downside is that the current implementation is not complete, and needs changes to the core / cache to solve the problem completely.

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Allow for more precise configurations, other than using the overridable configurations. An example would be to for example allow cache.config to specify different fuzzy parameters based on matching regular expressions.

Allow read-while-write to collapse immediately

We could perhaps allow read-while-write to allow immediate collapsed forwarding, IF a cached objects was going stale. It's reasonable to think that the refreshed version will also be cacheable, and it would be pretty safe to do this. We would of course have to deal the case where the response comes back as non-cacheable, then any additional collapsed connections must dislodge from the first connection, and initiate its own origin session.

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