RE: [squid-users] Can we use "no-cache" or "max-age=0" to refresh the cached objects

Thanks Amos,

Detailed explanation and Henrik's response helped us to find the proper
invalidation mechanism.

Cheers,
 Chris

> -----Original Message-----
> From: Amos Jeffries [mailto:squid3_at_treenet.co.nz]
> Sent: Thursday, October 02, 2008 1:01 PM
> To: Christian Tzolov
> Cc: squid-users_at_squid-cache.org
> Subject: Re: [squid-users] Can we use "no-cache" or "max-age=0" to
refresh
> the cached objects
>
> Christian Tzolov wrote:
> > Hi Amos,
> >
> >> Squid would request new data, I believe.
> >> Any time Squid receives new files from an authoritative source it
> > updates
> >> its cached copy with the new content (except possibly in cases of
bug
> > #7).
> >
> > I am scared by the "I believe" part :).
>
> Sorry for that. I'm sure current squid follow the RFC. Just not that I
> understand the RFC well, and have not yet put in the research to be
> authoritative on the answer.
>
> FWIW, if Mark or Henrik speak up they know a LOT more about these
issues
> than I do.
>
> >
> > 1. Can we relay on Squid to always update its cached content if the
> > response is newer (e.g. response has new Expires date and no other
> > validators)?
>
> If it *receives* newer data yes.
>
> The catch is bug #7, if squid receives newer headers, but not actually
a
> newer object.
>
> Some squid releases are subject to bug #7 on all traffic which gets
> swapped to disk cache. All current releases are subject to it under
> certain conditions.
> The best release which escapes most of the bug is currently
2.7.stable4.
> Though one side case with IMS requests was just fixed and solved this
> week.
>
> > 2. Squid does not change/optimize its behavior under high load in
way
> > that could affect assumption (1)?
>
> No Squid always uses the same optimal or sub-optimal behavior. The
only
> things which cause a change are re-configuration. Or a network failure
> causing a change in data source.
>
> > 3. If (1) holds is this a (HTTP) standard behavior or Squid
> > implementation?
>
> HTTP standard. Squid follows the RFC as closely as we can make it.
> Currently it follows the HTTP/1.0 standard closely, with as much as we
> can improved towards HTTP/1.1 behavior, which is backwards-compatible.
>
> Amos
>
> >
> > Thanks,
> > Chris
> >
> >> -----Original Message-----
> >> From: Amos Jeffries [mailto:squid3_at_treenet.co.nz]
> >> Sent: Thursday, October 02, 2008 4:05 AM
> >> To: Christian Tzolov
> >> Cc: squid-users_at_squid-cache.org
> >> Subject: Re: [squid-users] Can we use "no-cache" or "max-age=0" to
> > refresh
> >> the cached objects
> >>
> >>> Dear all,
> >>>
> >>> We have a Squid (2.6) server installed as a reverse proxy and
> > connected
> >> to
> >>> an original-server that uses the "Expire" header field to specify
> > when
> >> the
> >>> response should be considered stale.
> >>>
> >>> If the client requests includes a "no-cache" cache-control
directive
> > can
> >>> we assume that Squid will be forced to *reload* the cached object
> > with a
> >>> fresh response returned by the original server (assuming that the
> >> response
> >>> has a new expiration date set)?
> >>>
> >>> The HTTP header specification
> >>> (http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9.4)
> > says
> >>> that "the server MUST NOT use a cached copy when responding to
such
> > a
> >>> request" but does not say what should happen with the current
cached
> >>> object. Would it be replaced by new response?
> >>>
> >>> What would be the behavior of Squid in case of "max-age=0" request
> >>> directive (assuming again that the response has a newer expiration
> > date
> >>> set)?
> >> Squid would request new data, I believe.
> >> Any time Squid receives new files from an authoritative source it
> > updates
> >> its cached copy with the new content (except possibly in cases of
bug
> > #7).
> >> A few other things come in to play such as whether its allowed to
> > store
> >> the content returned, Vary, ETag etc.
> >>
> >> Amos
> >
> >
> >
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>
> --
> Please use Squid 2.7.STABLE4 or 3.0.STABLE9

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Received on Thu Oct 02 2008 - 16:02:21 MDT