On Tue, 22 Feb 2005, Marco Crucianelli wrote:
> Why shall I use never_direct? Maybe to force the frontend squid (the one
> caching web stuff) to never ask for multimedia files the origin servers,
> but to redirect these "calls" to the backend squid, the one caching
> multimedia stuff?!?
Yes..
> Maybe I've a wrong idea of how squid works!
Many are confused about the relations of cache_peer, never_direct and
always_direct etc.
cache_peer defines possible paths where Squid MAY forward the request.
cache_peer_access/cache_peer_domain limits when these paths may be
considered.
always_direct forces Squid to ignore all peers and always go direct for
the request.
never_direct (when always_direct is not in effect) tells Squid that it may
not go direct.
when neither always_direct or never_direct is in effect (the default
situation) Squid is free to choose whatever path it sees most fit for the
request, and will do this based on a number of criterias.
- type of request
- hierachy_stoplist
- prefer_direct on/off
- ICP status of the possible peers
- TCP status of the possible peers
- netdb information
- etc..
With the goal of finding a reasonable balance between global cache hit
ratio and request latency.
Normally it selects
1. The "best" ICP peer or Digest HIT peer.
2. Direct
3. Some parent (default, round-robin etc..)
If prefer_direct off then 2 and 3 switches place.
In never_direct then the picture looks somewhat different
1. The "best" ICP peer or Digest HIT peer.
2. Some parent (default, round-robin etc..)
3. All parents.
If always_direct then the picture becomes simply
1. Direct
Regards
Henrik
Received on Tue Feb 22 2005 - 16:00:04 MST
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