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Re: Strange performance discrepancy with proxy

From: Daniel Stenberg <>
Date: Fri, 15 Mar 2013 10:43:56 +0100 (CET)

On Wed, 13 Mar 2013, Matt Kunze wrote:

> We have recently integrated libcurl into our application to provide the
> underlying HTTP transport (replacing WinINET, which is a huge improvement,
> thanks!).

Nice. If you have anything additional to add to about this transition and possibly
some reasons for it, then do let us know!

> I'm seeing strange behavior where requests are _much_ faster when routed
> through a proxy (in this case the Fiddler diagnostic tool). Note that this
> is not a caching proxy, and all the requests are POSTs anyway, so I don't
> think that is the explanation. If I run the app with an HTTP_PROXY
> environment variable defined it is much faster than without - the code is
> the same in both cases. I've instrumented the code as well to display the
> progression of requests, and it appears to be the same in both cases except
> the proxied requests return much faster.

That is very curious indeed. There's in fact no particular different code path
within libcurl either! Using a proxy or a direct server will still use the
same functions and code, leading me to suspect that you see this difference
because of something in your network/setup that actually makes the proxy use
the network better... It isn't very easy for me to start guessing any more
details though.

I assume you're talking about plain HTTP here? What libcurl version are you
using on what Windows version?

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Received on 2013-03-15