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From Joshua Slive <>
Subject Re: [users@httpd] pipelined requests
Date Thu, 26 Jun 2003 14:08:10 GMT

I'm not really an expert on this area, but I can provide a little help.

On Wed, 25 Jun 2003, Kelly, Terence wrote:
> Does Apache 2.0 handle pipelined requests?

Yes.  It is a complete HTTP/1.1 implimentation.

> If so, does it handle them well/efficiently?

That's a rather vague question.

> For instance, if Apache httpd is running on
> a 4-CPU machine and it receives four pipelined
> requests to four different CGI scripts, are
> those scripts executed simultaneously (assuming
> that the machine is very lightly loaded when
> the requests arrive)?

My guess would be no.  In fact, I doubt that doing this would be in any
way reasonable for an http server.  For example, if the client requests
cgi1, cgi2, cgi3, and cgi4, in that order, and cgi4 starts to deliver
output before cgi1 is finished, what is the server supposed to do?  Queue
up all the output until the other three cgi scripts are finished?  Ouch!

No, in general pipelining was not designed to allow simultanous execution.
It was designed simply to minimize network latency by optimally filling up
network packets.

> My impression from non-authoritative sources
> (e.g., years-old material that I found out on the
> Web via Google) is that Apache httpd has handled
> pipelined requests since the late 1990s, but
> there have been both functionality and efficiency
> problems.  I haven't been able to determine which
> of these problems remain.

If you want any response to that, you'll need to provide more detailed

> A detailed description of how pipelined requests
> are handled by the implementation would be very
> helpful.

I don't think you'll find any such thing.  But you can always look at the


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