Cache Digests

From: Niall Doherty <>
Date: Fri, 11 Sep 1998 16:39:18 +0100


Some questions about Cache Digests maybe someone more familiar with
the code will be able to answer.

One of the main problems we had in our mesh was with FALSE HITs -
where a client asks a sibling for an object through HTTP after
ICP indicates it's present and it has been deleted in between the
two queries. I know it happens fairly infrequently but it causes lots
of grief for users.

The way around it is to allow all siblings to have miss_access. We
made this easier by setting up an automated list (using the cache-
announcements) of squid servers (29 now!). It works but it's not

So - we're just trying out Cache Digests now.

Will deletion from Cache Digests be supported in 1.2 ?

Has the only-if-cached solution to False Hits been implemented yet
in 1.2 for Cache Digest queries ?

Can this be used for HTTP queries that are a result of UDP_HITs ?
The server side of this should be easy to implement. The client
side should be the same for a HTTP query resulting from a

The paper on Cache Digests by DW and AR states that the current
implementation always forwards directly to the origin server if
there's no CACHE_DIGEST_HIT. If there are neighbours using ICP
I presume these will be used. If not, it wouldn't be possible to
reach the origin server if you're behind a firewall...

Have there been any other changes in the cache digest implementation
in Squid since the paper was written for the WWW Caching Conference ?


P.S. Does anyone know if any commercial products are/will be supporting
Cache Digests soon ?

Niall Doherty          |
Systems Engineer       |
Voice: +353 1 207 7506 | Ericsson Systems Expertise Ltd.,
Fax:   +353 1 207 7115 | Beech Hill, Clonskeagh, Dublin 4, Ireland.
Received on Fri Sep 11 1998 - 08:41:01 MDT

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