obj.cacheable vs expires headers?

Luc Stroobant lstroobant at gmail.com
Mon Feb 8 21:39:28 CET 2010

Poul-Henning Kamp wrote:
> In message <4B707314.5090205 at gmail.com>, Luc Stroobant writes:
>> obj.ttl seems to be zero indeed, but I still don't get how his would 
>> make the request cacheable. At least it's not the behaviour one would 
>> expect?
> We distinguish between "can be cached" and "how long should it be cached"
> because they are very different questions.
> "can be cached" is a matter of correctness, whereas "how long" is 
> just a performance issue.

So you mean: the object /can/ be cached, but it would only be cached for 
zero seconds?

>> Secondly: I also thought that Varnish never caches requests with a 
>> Set-cookie header?
> Varnish has a special kind of cache entries called "hit-for-pass".
> This is a cache entry that says that the object can not be cached,
> that solves a pile-up issue on busy objects.
> The fact that you see zero TTL, can be indicative of the clock on
> the varnish-host and the clock on the backend not agreeing what
> time it is.  Check your ntpd.

I don't think it's a clock issue. Varnish and the webserver are running 
on the same host. We wanted to use Varnish to cache some static files on 
an overloaded prefork Apache + mod-php (and it did a great job, till we 
started to see weird session issues).


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