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Re: Pipelining and compression effect on HTTP/1.1 proxies

From: Henrik Frystyk Nielsen <frystyk@w3.org>
Date: Tue, 22 Apr 1997 17:52:57 -0400
Message-Id: <3.0.1.32.19970422175257.00985b70@pop.w3.org>
To: Benjamin Franz <snowhare@netimages.com>, http-wg@cuckoo.hpl.hp.com
At 12:16 PM 4/22/97 -0700, Benjamin Franz wrote:

>My figures on www.xmission.com (a large server with many different
>commercial and non-commercial residents) from a sample of 27 gigabytes of
>recent measured traffic indicates that only about 13% of the traffic is
>text/*.  This slashes the potential savings to a mere 13% x 57.5% = 7.5%
>from compressing the text/* files. And this overlooks the fact that the
>majority of people browsing are doing so over modem links that *already*
>perform pretty good on the fly compression of the data flowing through
>them - thus reducing the potential savings to the end user from
>pre-compressing text/* to negligible.

Figures showing (potentially lack of) savings using compression compared to
all other data formats are all very good, but is in fact not what our data
results are all about.

1) In typical browsing mode, the very first packet on a connection contains
an HTML page - the images are not requested until the HTML has arrived and
started being parsed. TCPs behavior over time is a non-linear function
where the first packet is much more expensive than the last. Therefore, it
is likely to be a win to concentrate our efforts on the first packet. This
is exactly what compressing HTML gives us.

2) Modem compression has on several occasions been indicated to have
"pretty good" performance. Our data show otherwise - but not explicitly. I
just made some simple tests of modem compression with and without deflated
data and the figures are compelling - gaining about 2/3 in both time and
packets when using deflate. Look at

   http://www.w3.org/pub/WWW/Protocols/HTTP/Performance/Compression/PPP.html

for details. Compression also helps on a LAN - see the figures at

   http://www.w3.org/pub/WWW/Protocols/HTTP/Performance/Compression/LAN.html

3) On the more speculative side, I don't consider the current composition
of data formats in caches being constant. The paper describes the potential
benefits of using style sheets and other data formats than the more
traditional gif and jpeg. Style sheets are just starting to be deployed and
it may change the contents significantly over the next 6 months. CSS1 style
style sheets compress just as well as HTML, so there is yet another point
counting for compression.

So, the _actual_data_ that we have now for the effect of compression seems
to indicate with little doubt that it is worth doing!

Thanks,

Henrik
--
Henrik Frystyk Nielsen, <frystyk@w3.org>
World Wide Web Consortium, MIT/LCS NE43-346
545 Technology Square, Cambridge MA 02139, USA
Received on Tuesday, 22 April 1997 14:57:57 EDT

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