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Re: ra_dav compression question

From: Branko Čibej <brane_at_xbc.nu>
Date: 2003-06-24 01:42:44 CEST

cmpilato@collab.net wrote:

>Chris Hecker <checker@d6.com> writes:
>>A delta/diff is different from a compressed stream. Sure, it's not
>>sending the parts that didn't change, but the changes aren't
>>compressed (and, as someone said, adds are the special case where it
>>all changes), if I understand things correctly. Not that sending
>>diffs isn't great, but you really want the compression to go both
>>ways, especially since that's part of the reason one is supposed to
>>use apache as the server from the manual ("wire compression for free").
>Generally speaking, you're correct. But Subversion uses a binary
>diffing format that not only sends just the differences, but even
>those differences are transmitted in a gzip-like fashion. I forget
>the stats someone figured out, but there definitely is some
>compression going on.
Quite a lot, actually. The last numbers I got are that we're within 10%
of "diff -e | gzip -9", and we'll beat that consistently once Dan
Berlin's svndiff patch goes in (i.e., once I get the time and
inclination to finally bring it up to date).

> In other words, if your differences are that
>you added the phrase "Chris is a pleasant programmer" in ten different
>places through a file, the trasmitted data might list that string only
>once, and then refer to it ten times.
It gets even better than that -- the two "is " in there would get
compressed to one, probably. :-)

>Additionally, as you noted, we can have real Zlib compression on top
>of that, compliments of Apache and Neon.
Yeah. And I'm wondering if compressing our delta stream is really worth
the effort.

Brane Čibej   <brane_at_xbc.nu>   http://www.xbc.nu/brane/
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Received on Tue Jun 24 01:43:31 2003

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