Re: [squid-users] Two squid instances based on file types? Is it good?

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