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From "Bill Stoddard" <b...@wstoddard.com>
Subject Re: Piplined requests in HTTP/1.1
Date Thu, 22 Mar 2001 01:36:17 GMT

>
> Yes, pipelined requests are really used.  They are a huge performance win,
> because fewer packets are used for the same request.
>
Where have you seen them used?  Jeff says IE 5.? may use them.

Yea, I know what they are for and how they work. The biggest win in pipelined requests is
the
reduced latency (i.e., you don;t have to wait a round trip for each and every request/response
pair). I suspect pipelined requests don't significantly reduce the number of packets sent
except in
somewhat contrived or special cases where responses to requests are significantly smaller
than an
ethernet packet payload.

And my rub is this... Apache has a lot of code path dedicated to checking for pipelined requests.
Apache 1.3 ap_bhalfduplex does an extra select on almost every single request, regardless
of whether
the connection is HTTP/1.0, HTTP/1.1, keep-alive or not (2.0 does similar things) all because
the
client -might- pipeline a request.  That extra select is expensive. Thus my question if pipelined
requests are really being used.

Bill


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