[squid-users] Understanding the use of must-revalidate/proxy-revalidate

Hi all,

I'm struggling with the configuration of a PHP based content management system served from Apache behind a squid 2.6 reverse proxy. Specifically, it's serving out stale content, ie. responses that are past their "Expires" time.

I've added "must-revalidate" to the "Cache-Control" header but squid is still caching the (old) response. I thought it would re-cache the URL after the "Expires" time. Is that not the case?

Also note, the application is configured to send a "304 Not Modified" Status-Code where appropriate.

This request was made at Mon, 20 Sep 2010 05:05:45 GMT but is still being severed by squid hours after becoming "stale".

HTTP/1.0 200 OK
Date Sun, 19 Sep 2010 03:42:44 GMT
Server Apache/2.2.3 (Red Hat)
X-Powered-By PHP/5.1.6
Expires Sun, 19 Sep 2010 12:34:05 GMT
Cache-Control max-age=43200, public, must-revalidate
Pragma cache
Last-Modified Fri, 17 Sep 2010 06:50:06 GMT
Vary Accept-Encoding,User-Agent,X-SSL
Content-Encoding gzip
Content-Length 5009
Content-Type text/html; charset=utf-8
Age 1
X-Cache HIT from webcms-prod02.mysite.com
X-Cache-Lookup HIT from webcms-prod02.mysite.com:3128
Via 1.0 webcms-prod02.mysite.com:3128 (squid/2.6.STABLE21)
Connection keep-alive

--
Regards,
Sean.
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