Re: New Version Notification for draft-vkrasnov-h2-compression-dictionaries-01.txt

Jyrki Alakuijala <jyrki@google.com> Thu, 03 November 2016 10:36 UTC

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From: Jyrki Alakuijala <jyrki@google.com>
Date: Thu, 3 Nov 2016 11:32:14 +0100
Message-ID: <CAPapA7TfTMdOA4XB=9b6959CUxqfZFe=A8nVnQB3xd3pG8HBRg@mail.gmail.com>
To: Vlad Krasnov <vlad@cloudflare.com>
Cc: Matthew Kerwin <matthew@kerwin.net.au>, Martin Thomson <martin.thomson@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
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Subject: Re: New Version Notification for draft-vkrasnov-h2-compression-dictionaries-01.txt
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On Thu, Nov 3, 2016 at 6:43 AM, Vlad Krasnov <vlad@cloudflare.com> wrote:

> This is indeed not unlike SDCH and “quasi dictionaries” only your
> dictionary defined by a stream and not a different url. In fact it can be
> used with SDCH just as well.
> My proposal tries to be as algorithm agnostic as possible.
> However brolti compresses much better in that case. In fact from what I
> have seen brotli+”quasi” beats sdch+”quasi”+brotli (but maybe
> sdch+”quasi”+brotli+”quasi” will do even better?).
>

Yes, this is consistent with our experiments. Brotli + custom dictionary is
more efficient than SDCH + custom dictionary with further gzip or brotli
compression.

With small (~150 kB) dictionaries brotli wins SDCH by 10-20 % (20 % at
brotli quality 11, 10 % at quality 6), with larger (1 MB) dictionaries
more, 20-30 % (30 % at brotli quality 11, 20 % at quality 6). The larger
the custom dictionary, the more powerful brotli comes in comparison to
SDCH. All our experiments indicate that SDCH is fully redundant and can be
abandoned if we add custom dictionary support to brotli content encoding.