Re: QPACK proposal: wrap absolute index values

Dmitri Tikhonov <dtikhonov@litespeedtech.com> Mon, 06 August 2018 03:33 UTC

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Date: Sun, 5 Aug 2018 23:33:30 -0400
From: Dmitri Tikhonov <dtikhonov@litespeedtech.com>
To: Ryan Hamilton <rch=40google.com@dmarc.ietf.org>
Cc: Martin Thomson <martin.thomson@gmail.com>, QUIC WG <quic@ietf.org>
Subject: Re: QPACK proposal: wrap absolute index values
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On Sun, Aug 05, 2018 at 08:14:55PM -0700, Ryan Hamilton wrote:
> Do we have any sense on the overall impact on compression efficiency base
> on typical HTTP workloads?

The "typical" part is somewhat subjective.  The impact is on compression
would be more pronounced in scenarios where the header blocks are smaller
(meaning that the dynamic table has slower churn).  For example, a small
HAR I've been working with as example to our QPACK implementation contains
18 requests.  The header blocks and the encoder stream compress to about
1 KB.  An overhead of 2 bytes per header block would translate to

    18 * 2 / 1024 = ~4%

The penalty is not dramatic, but it's not insignificant, either.

  - Dmitri.