On Thu, 4 Dec 2003, Manfred Milhofer wrote: > Now, I have already started to learn the Apache techniques to configure > these headers (Apache powers Oracle Portal), but my question is this: > given the lack of freshness information here, would it not be expected > for a proxy server to always retrieve from the origin server, in case > its cached copy was out of date?
No. It is to be expected that proxy servers will apply heuristics based on the document age (Date - Last-Modified) for guessing when it needs to recheck with the origin server. In case of Squid this heuristics defaults to 20% of the document age. > Or is it precisely this lack of information that would lead to > inconsistent results (which has been the client's experience), i.e. > sometimes getting the up to date document, sometimes not. Correct. And by adding the proper headers you can give more accurate information to the caches. In the optimal case it is known when the document will be updated next and in such case a Expires header should be used. But most often the best that can be done is to instruct caches that they must recheck the freshness of the object if it is older than X. Regards Henrik
