Varnish bypassing cache when if-modified-since header present?

Poul-Henning Kamp phk at
Mon Jul 2 21:07:24 CEST 2007

In message <20070702182201.GF5005 at>, Mike Hedlund writes:
>Hey guys,
>       I've been playing with varnish for the last few days, trying
>to eval it as a squid replacement my image serving farm. I enabled
>it on one of the squids friday (replacing 2 seperate squid processes
>on a single server), and seen pretty awesome results:

That's a pretty typical experience :-)

>[...] varnish config is always re-validating
>if-modified-since headers (when supplied by the client)[...]

This shouldn't happen, but there is on case where it will: if your
varnish and backend don't agree what time it is.

Could you check that ?

If you want to fill in some debugging look for "res_do_304" in

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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