Re: Squid 2.2 and cache-digest misses?

Hi,

> tested cache-digests but they yielded quite high false-hit ratio
> (resulting in numerous 'Forwarding Denied' error messages) so we had to
> abandon them completely and stick to the good old ICP.

You're not the only one who sees high numbers of False Hits. Check the
FAQ section on Cache Digests - there's a little bit in there that might
help you track down why the False Hits are occurring (I haven't had time
to figure it out yet :-)

Cache Digest Debugging:
  http://squid.nlanr.net/Squid/FAQ/FAQ-16.html#ss16.13

The previous questions/items fill in any info that's required...

> As Squid 2.2 announces the ability to retry failed requests that report
> 504 Gateway Timeout, a question comes out whether the same mechanism
> will be used to process cache-digest false-hits on siblings. This way we
> could use them in spite of false-hits and thus reduce the ICP bandwidth
> overhead and delays.

I'm running 2.2.PRE2 on 2 caches here and I see the reported behaviour.
When a False Hit occurs the sibling shows a 504 error (while before it
either showed access_denied or else, if miss_access was allowed, the
"normal" retrieval method through parents/direct etc.). The local squid
logs do NOT show a CACHE_DIGEST_HIT now. They will show something else,
e.g. going direct or through parent.

So - yes it should be fine to use Cache Digests now with your siblings.
As far as I know, older versions of Squid 2 answered correctly (with 504)
*if* the only-if-cached HTTP header was used (but Squid wasn't using it
in requests - is this right Alex/Duane ?) so they should be ok.

Let us know how it goes ! especially if you get more info on the high
numbers of False Hits.

Cheers,
Niall

PS The FAQ needs to be updated - I'll do it when Squid 2.2 is RELeased.

-- 
Niall Doherty, Systems Engineer          mailto:ndoherty@eei.ericsson.se
Ericsson Systems Expertise Ltd.,                  Voice: +353 1 207 7506
Beech Hill, Clonskeagh, Dublin 4, Ireland.          Fax: +353 1 207 7115
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