On Mar 4, 2009, at 6:44 AM, JimL wrote:


Thanks Ric,

this is really helping.

I've just noticed the:

Cache-Control: max-age=0, s-maxage=0, private, must-revalidate

header. I'm no expert on any of this, but from what I've just been reading, the max-age=0 means that content is never fresh and Varnish is contacting
the backend every time (i.e. not caching)?

Let me know if I'm wrong. If so that would explain why the performance is
just a tiny bit slower than Plone on its own.

Cheers,  Jim



For shared caches, both 'private' and 's-maxage' take precedence over 'maxage' but the practical effect is the same. This response is never stored in shared caches. It can be stored in the browser cache but is immediately stale (because of 'maxage') which forces a validation header on the next request.

This is the set of headers that you get with CacheFu. The page matches the 'plone-content-types' cache rule, which delegates authenticated requests to 'cache-in-memory' and anonymous to 'cache- with-etag'. Take a look at both header sets in the CacheFu control panel and you'll see all those cache-control tokens set.

The tiny performance difference may just be the extra hop that varnish introduces into the chain. Not usually significant and as Martin already pointed out, more than offset by the speedup of the varnish- cached resources like inline images, css, and javascript.

Ric



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