Re: Deadlocking in the transport

Martin Thomson <martin.thomson@gmail.com> Wed, 10 January 2018 21:54 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Thu, 11 Jan 2018 08:54:03 +1100
Message-ID: <CABkgnnVFHu6UhdUJYLUKXJyz7oGVdqKpaYz=eEhUR5_nNOQeXw@mail.gmail.com>
Subject: Re: Deadlocking in the transport
To: "Brian Trammell (IETF)" <ietf@trammell.ch>
Cc: QUIC WG <quic@ietf.org>
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On Wed, Jan 10, 2018 at 6:04 PM, Brian Trammell (IETF) <ietf@trammell.ch>; wrote:
> Do we have any actual numbers on how much efficiency can actually be squeezed out of allowing compression dictionaries to create unbounded dependencies between streams on common, non-pathological workloads?

Dmitri ran some tests with QMIN, which doesn't create dependencies,
and found that for a time compression efficiency degraded noticeably
if it couldn't create dependencies.  I'll let Dmitri speak to that
point.  The shortcoming rectifies itself reasonably quickly, though
Roberto makes the point that this is precisely the point where
compression matters most.  It's a point that the header compression
folks are still debating.

(The dependencies wouldn't be unbounded.  One advantage of the
mechanism that QMIN proposes is that these dependencies are pretty
narrowly constrained and well understood.)