Re: [squid-users] Collapsed forwarding question

tor 2007-05-17 klockan 19:33 -0400 skrev BARRY J BLUMENFELD:
> Hello,
> We have made some progress. We actually have two squids in parallel with DNS load balancing.
> We had been running them as each others parents so that we could try to reduce the load on the backend server. If we stop cache_peering, then the timeouts go away. The relevant lines
> for server1 are
> cache_peer server2.domain parent 3128 3130
> acl SERVER src server1.domain server2.domain
> cache_peer_access server2.domain allow !SERVER

That way might end up with request loops then depending on timing of the
requests to two servers, and due to collapsed_forwarding the loop isn't
noticed.

Explanation: Two different requests for the same URL hits both servers
at approximately the same time. They both forward to the other and
deadlock with the two waiting on each other and none talking to the
origin..

> We configure the two as parents rather than as siblings, because, for an expired file, squid won't
> bother querying a sibling. So, at this point, we have a choice between collapsed_forwarding or
> the cache_peer relationship. Is there some better configuration setup we can try?

You could look into removing the sibling restriction from cache
validations. But be warned that it's there to stop cache bouncing where
old content in some conditions ends up bouncing between the servers.

Deploying a second layer of proxies is one solution.

Implementing intra-array CARP routing another. Currently only
inter-array CARP routing exists in Squid.

The end goal of the above two solutions is to ensure that for each given
URL there is always one designated proxy which is responsible for
fetching this URL from the origin server, and that data then propagates
out to the other from there. This way request routing and freshness is
fully deterministic.

Regards
Henrik