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Gzip useful or not (was: "Going fast on the Mobile Web" - input for MWABP?)

From: Dominique Hazael-Massieux <dom@w3.org>
Date: Tue, 01 Jul 2008 13:40:55 +0200
To: Rotan Hanrahan <rotan.hanrahan@mobileaware.com>
Cc: public-bpwg <public-bpwg@w3.org>
Message-Id: <1214912455.7290.15.camel@altocumulustier>

Le mardi 01 juillet 2008 à 07:24 -0400, Rotan Hanrahan a écrit :
> This is particularly the case when delivering a rich presentation. A
> mobile page will be relatively simple in terms of its text content,
> and (hopefully) not too complex with respect to scripting (if
> present), and there will probably be a few images too. The image
> payload of a rich presentation will be the significant majority, and
> if JPEG is used, this majority portion of the data is already
> compressed.

I think that while this is most likely true for mobile web pages, when
considering mobile web applications, the equation becomes a bit more
complicated - you may actually be hitting large javascript files, or
large data set retrieved through AJAX operations.

I think there are 2 key questions to consider when deciding whether
something should be sent gzipped or not (if the browser supports it,
obviously):
 * the amount of time saved by downloading less data must be superior to
the amount of time taken to decompress the data; the first depends on
the compression rate and the bandwidth considered, the second on the
performance of the CPU. I'm still trying to collect data on these
parameters to see if there are good thumb rules we could give in the
MWABP
 * resources that are served compressed cannot be rendered progressively
(i.e. as data come in through the pipes), creating a perceived latency
from the user perspective, so should probably be avoided for
technologies that can use progressive rendering; typically, gzipping a
javascript file is likely more interesting than gzipping a big HTML
file, since that would prevent the browser from starting to render it
before it completed the download

More data on this later, hopefully.

Dom
Received on Tuesday, 1 July 2008 11:42:18 UTC

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