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Re: FSFS format7 and compressed XML bundles

From: Ben Reser <ben_at_reser.org>
Date: Fri, 1 Mar 2013 18:31:32 -0800

On Fri, Mar 1, 2013 at 5:49 PM, Julian Foad <julianfoad_at_btopenworld.com> wrote:
> No, that's not true. I think the article Ben read was inaccurate. The '--rsyncable' option doesn't reset the compression after a fixed number of bytes, but rather at every point where a rolling checksum of the last N bytes leading up to that point has a certain value. It will resynchronize after an insertion or deletion. The intervals between resets are irregular but deterministic.
>
> Here's an old but readable description and proof-of-concept: <http://svana.org/kleptog/rgzip.html>.
>
> Here's an announcement of implementation in pigz: <http://mail.zlib.net/pipermail/pigz-announce_zlib.net/2012-January/000003.html>. It's described in more detail in a big comment near the beginning of 'pigz.c' in the source tarball available at <http://zlib.net/pigz/>.

This is the patch that Debian is actually applying to gzip:
http://ozlabs.org/~rusty/gzip.rsync.patch

This was the article I had read which sadly is misleading:
http://beeznest.wordpress.com/2005/02/03/rsyncable-gzip/

Julian is right, the window is rolling and so it works for inserts and
deletions.
Received on 2013-03-02 03:32:21 CET

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