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Originally Posted by danielf
Ah, that makes sense, as I was wondering if the proxy had to query for a more recent page, which would increase traffic and defeat the purpose of the proxy unless you only have to retrieve the time stamp of the most recent page.
I presume this expiry time/date is set differently depending on the type of page? (very low for a forum like this) and high(er) for less dynamic pages)?
Or is it just based on recent 'refresh rates'?
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One important thing to note is that a web page is made up of several objects, each of which can have different cacheability HTTP headers:
- Expires (the best since they are explictly set by the content publisher)
- Cache-Control
- Last-Modified
So a forum page should have the frequently updated part as having either a very recently modified date, a short expiry time or else marked as non-cacheable and the relatively static parts (logos, banners etc.) as being older or having longer expiry times.
This will make the page much more responsive than making the whole page uncacheable. Note that these settings are what your local browser cache uses as well, so it's not just for the benefit of proxies).
In fact checking this page via the Cacheability Engine shows this to be true (takes some time to load):
http://www.web-caching.com/cgi-web-c...php%3Ft%3D9354
There's some more info about how this all works (without requiring knowledge of the RFCs) and how to optimise web servers at:
http://www.mnot.net/cache_docs/