Re: [squid-users] How get negative cache along with origin server error?

Do any of the squid experts have any answers for this?

- Dave

On Thu, Sep 25, 2008 at 02:04:09PM -0500, Dave Dykstra wrote:
> I am running squid on over a thousand computers that are filtering data
> coming out of one of the particle collision detectors on the Large
> Hadron Collider. There are two origin servers, and the application
> layer is designed to try the second server if the local squid returns a
> 5xx HTTP code (server error). I just recently found that before squid
> 2.7 this could never happen because squid would just return stale data
> if the origin server was down (more precisely, I've been testing with
> the server up but the listener process down so it gets 'connection
> refused'). In squid 2.7STABLE4, if squid.conf has 'max_stale 0' or if
> the origin server sends 'Cache-Control: must-revalidate' then squid will
> send a 504 Gateway Timeout error. Unfortunately, this timeout error
> does not get cached, and it gets sent upstream every time no matter what
> negative_ttl is set to. These squids are configured in a hierarchy
> where each feeds 4 others so loading gets spread out, but the fact that
> the error is not cached at all means that if the primary origin server
> is down, the squids near the top of the hierarchy will get hammered with
> hundreds of requests for the server that's down before every request
> that succeeds from the second server.
>
> Any suggestions? Is the fact that negative_ttl doesn't work with
> max_stale a bug, a missing feature, or an unfortunate interpretation of
> the HTTP 1.1 spec?
>
> By the way, I had hoped that 'Cache-Control: max-stale=0' would work the
> same as squid.conf's 'max_stale 0' but I never see an error come back
> when the origin server is down; it returns stale data instead. I wonder
> if that's intentional, a bug, or a missing feature. I also note that
> the HTTP 1.1 spec says that there MUST be a Warning 110 (Response is
> stale) header attached if stale data is returned and I'm not seeing
> those.
>
> - Dave
Received on Tue Sep 30 2008 - 15:38:37 MDT