Re: A start at a users guide

From: <>
Date: Mon, 27 Jan 97 09:48:33 +0000

There must be alot of useful FAQ type responses in the squid-users

At the dumbest level, here's my answer to an "What's accelerator
mode?" email to squid-users.
I have occasionally had trouble explaining accelerators and proxy
caches, usually resulting from mixed up interpretations of "incoming"
and "outgoing". I think in terms of requests; i.e. an outgoing request
is from the local site out to the big bad Internet; the data received
in reply is incoming, of course. Others think in which is the opposite
sense of "a request for incoming data",

An accelerator caches incoming requests for outgoing data, i.e. that
which you publish to the world. It takes load away from your HTTP
server and internal network. You move the server away from port 80 (or
whatever your published port is), and substitute the accelerator,
which then pulls the the HTTP data from the "real" HTTP server (only
the accelerator needs to know where the real server is). The outside
world sees no difference (apart from an increase in speed, with luck).

Quite apart from taking the load of a site's normal web server,
accelerators can also sit outside firewalls or other network
bottlenecks and talk to HTTP servers inside, reducing traffic across
the bottleneck (persistent tcp connections?) and simplifying the
configuration. Two or more accelerators communicating via ICP can
increase the speed and resilience of a web service to any single

The Squid redirector can make one accelerator act as single front end
for multiple servers. If you need to move parts of your filesystem
from one server to another, or if separately administered HTTP servers
should logically appear under a single URL hierarchy, the accelerator
makes the right thing happen. We're in the process of a major
filesystem move, which will be greatly helped by this; we're also
looking at authenticated connections, POSTs and various other changes
to HTTP server functions which can be piloted and developed separately
from the main server by hiding them behind an accelerator.

If you wish only to cache the "rest of the world" to improve local
users browsing performance, then accelerator mode is irrelevant.
Sites which own and publish a URL hierarchy use an accelerator to
improve other sites' access to it. Sites wishing to improve their
local users' access to other sites' URLs use proxy caches. Many sites,
like us, do both and hence run both.

Peter Lister Email:
Computer Centre, Cranfield University Voice: +44 1234 754200 ext 2828
Cranfield, Bedfordshire MK43 0AL UK Fax: +44 1234 751814

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Received on Mon Jan 27 1997 - 01:59:19 MST

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