This is not a response to any post on this subject, but more of a comment. Here is a real world example of how we use deflate and etags with our cache. (Note this is very similar to mod_cache, but I do not know the inner workings of it as well).

1. Generate key from URI and ap_get_servername
2. open cached object.  Is it "Vary?" no, goto step 5.
3. Is "Vary." Generate new key.
4. Open cached object.
5. Check expiry time, "exit" if expired.
6. Load headers.
7. Call ap_meets_conditions (etags, IMS, etc.)  If yes, return 304 (or 
whatever).
8. If not meets_conditions, serve from cache.

So, multiple variants of the same object can have the same Etag, but still be different cached objects.

This probably has no bearing on the current conversation, but perhaps I am not fully appreciating the core of the debate??

--
Brian Akins
Chief Operations Engineer
Turner Digital Media Technologies

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