HTTP Cache Control max-age, must-revalidate

Question

I have a couple of queries related to Cache-Control.

If I specify Cache-Control "max-age=3600, must-revalidate" for a static html/js/images/css file, with Last Modified Header defined in HTTP header,

a. Does browser/proxy cache(liek Squid/Akamai) go all the way to orgin server to validate before max-age expires? Or will it serve content from cache till max-age expires?

b. After max-age expiry(that is expiry from cache), is there a IMS check or is content re-downloaded from origin server w/o IMS check?

Answer 1

a. Look at the ‘Stats’ tab on this page and see what happens.

b. After expiration the browser will check at the server if the file is updated. If not, the server will respond with a 304 Not Modified header and nothing is downloaded.

You can check this behaviour yourself by looking at the ‘Net’ panel in Firebug or similar tools. Just re-enter the URL in the address bar and compare the number of HTTP requests with the number of requests when your cache is empty.