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Re: Lost initial MAX_PUSH_ID is unfortunate

Lucas Pardue <lucaspardue.24.7@gmail.com> Wed, 28 August 2019 19:27 UTC

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From: Lucas Pardue <lucaspardue.24.7@gmail.com>
Date: Wed, 28 Aug 2019 20:27:26 +0100
Message-ID: <CALGR9oavwv9n1+EH6zmzCwQkbfTh=bvag0NfeiN9UsvP-e-Wtw@mail.gmail.com>
Subject: Re: Lost initial MAX_PUSH_ID is unfortunate
To: Nick Harper <nharper=40google.com@dmarc.ietf.org>
Cc: QUIC WG <quic@ietf.org>
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Lets take an extreme case, the client sends an initial max push ID of 1. On
the first request the server sends a push promise - now its out of credit
when chances are it wanted to push more than one thing. So it's back to
"waiting" for a MAX_PUSH_ID or just giving up on push. The server needs all
the logic to manage this exhaustion case.

I think we are ok with what we have. But if we want off the wall ideas:
allow MAX_PUSH_ID frames on request streams before HEADERS (solving the
sequencing problem) and relax the rules for connection errors on limit
decrement.

On Wed, 28 Aug 2019, 19:39 Nick Harper, <nharper=40google.com@dmarc.ietf.org>
wrote:

>
>
> On Tue, Aug 27, 2019 at 8:00 PM Martin Thomson <mt@lowentropy.net> wrote:
>
>> On Wed, Aug 28, 2019, at 08:48, Ryan Hamilton wrote:
>> > In some testing we've been doing, we realized that if the packet
>> > containing the initial MAX_PUSH_ID frame is lost (or reordered until
>> > after the first request) then the server is unable to push responses.
>> > This is a bit unfortunate. We could, of course, bundle the MAX_PUSH_ID
>> > with all packets that send a new request until the MAX_PUSH_ID is
>> > ACK'd. This feels a tad inelegant and I wondered if there's any
>> > appetite for an alternative.
>>
>> I don't think that this is great justification for that sort of change.
>> We explicitly removed head of line blocking from the processing of
>> SETTINGS.  In practice, I suspect that this situation also results in no
>> access to QPACK also.
>>
>> Performance might suffer, but at least you can send something sensible in
>> a round trip when you would otherwise (with h2 for instance) be twiddling
>> thumbs.
>>
>> Why can't we have the best of both worlds? If we put this signal in the
> crypto handshake, the application protocol can guarantee that it arrives
> before any STREAM frames, and we don't introduce any more head of line
> blocking because the connection is already blocked on the crypto handshake
> messages to derive 0-RTT or 1-RTT application data keys.
>

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