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From Graham Leggett <minf...@sharp.fm>
Subject Re: mod_proxy Cache-Control: no-cache=<directive> support Apache1.3
Date Wed, 06 Mar 2002 18:29:05 GMT
Igor Sysoev wrote:

> mod_accel is not proxy. It's accelarator. It can not work as usual proxy.
> I did not even try to implement it - Apache 1.3 is poor proxy. Squid or
> Oops are much better.

Until recently you were not aware that the proxy had been updated - I
would look at the code again before passing this judgement ;)

For example, you pointed out some problems with Squid and content
negotiation - mod_proxy doesn't have these problems.

> mod_accel can ignore client's 'Pragma: no-cache' and
> 'Cache-Control: no-cache'. These headers are sent if you press Reload
> button in Netscape or Mozilla. By default if mod_accel gets these headers
> then it does not look cache but send request to backend.
> Webmaster can set 'AccelIgnoreNoCache on' if he sure that
> backend did not give fresh data and such requests only overload backend.

This design is broken.

If the client sent a cache-control or pragma header it was because the
client specifically wanted that behaviour. If this causes grief on the
backend, then your backend needs to be redesigned so that it does not
have such a performance hit.

Breaking the HTTP protocol isn't the fix to a broken backend.

> > In theory mod_proxy (and mod_cache) should allow results to be logged
> > via the normal logging modules. If this is not yet possible, it should
> > be fixed.
> 
> In theory but not in practice.

Then it needs fixing.

> > Everything under /blah is proxied, except for everything under
> > /blah/somewhere/else.
> 
> Yes. But '!' is already implemented ?

Yes it is.

> > > *) proxy mass name-based virtual hosts with one directive on frontend:
> > >    AccelPass   /      http://192.168.1.1/    [PH]
> > >    [PH] means preserve hostname, i.e. request to backend would go with
> > >    original 'Host' header.
> >
> > mod_accel does this in one directive, mod_proxy does it in two - but the
> > effect is the same. Should we consider adding a combined directive to
> > mod_proxy the same way mod_accel works...?
> 
> What are two mod_proxy's directives ?
> As far as I know mod_proxy always change 'Host' header.

Use the ProxyPreserveHost option.

> No. mod_proxy tries it but code is broken. If connection failed it try
> to connect with the same socket. It should make new socket.
> Anyway mod_accel tries another backend if connection failed, backend
> has not sent header, and backend has send 5xx response.

This should be fixed.

> mod_accel can send part of answer to client even backend has not sent
> whole answer. But even in this case slow client never block backend -
> I use nonblocking operations and select().
> Would it be possible with mod_cache ?

The idea behind mod_cache was to separate the "send" threads from the
"receive" thread. This means that if a response is half-way downloaded,
and a new request comes in, the new request will be served from the
half-cached half-downloaded file, and not from a new request. When the
original request is finished, the backend is released, and the "receive"
threads carry on regardless.

> > Both busy locks and limiting concurrent connections can be useful in a
> > normal Apache server using mod_cgi, or one of the Java servlet
> > connectors. Adding this to proxy means it can only be used in proxy -
> > which is a bad idea.
> 
> Probably but Apache 1.3.x has not such module and I needed it too much
> in mod_accel.

You should have created a separate module for this, and run it alongside
mod_accel. This can still be done though.

> > This is the job of mod_rewrite.
> 
> mod_rewrite can not do it.

Then rewrite should be patched to do it.

Regards,
Graham
-- 
-----------------------------------------
minfrin@sharp.fm		"There's a moon
					over Bourbon Street
						tonight..."
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