Re: Design Issue: Max Concurrent Streams Limit and Unidirectional Streams
James M Snell <jasnell@gmail.com> Wed, 01 May 2013 17:28 UTC
Return-Path: <ietf-http-wg-request@listhub.w3.org>
X-Original-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Delivered-To: ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 1D1FC21F9A07 for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Wed, 1 May 2013 10:28:10 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -10.411
X-Spam-Level:
X-Spam-Status: No, score=-10.411 tagged_above=-999 required=5 tests=[AWL=-0.112, BAYES_00=-2.599, MIME_8BIT_HEADER=0.3, RCVD_IN_DNSWL_HI=-8]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Yi4u-GqRiJFy for <ietfarch-httpbisa-archive-bis2Juki@ietfa.amsl.com>; Wed, 1 May 2013 10:28:03 -0700 (PDT)
Received: from frink.w3.org (frink.w3.org [128.30.52.56]) by ietfa.amsl.com (Postfix) with ESMTP id B84AC21F9A64 for <httpbisa-archive-bis2Juki@lists.ietf.org>; Wed, 1 May 2013 10:28:03 -0700 (PDT)
Received: from lists by frink.w3.org with local (Exim 4.72) (envelope-from <ietf-http-wg-request@listhub.w3.org>) id 1UXaoN-0006jb-82 for ietf-http-wg-dist@listhub.w3.org; Wed, 01 May 2013 17:27:23 +0000
Resent-Date: Wed, 01 May 2013 17:27:23 +0000
Resent-Message-Id: <E1UXaoN-0006jb-82@frink.w3.org>
Received: from lisa.w3.org ([128.30.52.41]) by frink.w3.org with esmtp (Exim 4.72) (envelope-from <jasnell@gmail.com>) id 1UXaoD-0006hh-Jm for ietf-http-wg@listhub.w3.org; Wed, 01 May 2013 17:27:13 +0000
Received: from mail-ob0-f180.google.com ([209.85.214.180]) by lisa.w3.org with esmtps (TLS1.0:RSA_ARCFOUR_SHA1:16) (Exim 4.72) (envelope-from <jasnell@gmail.com>) id 1UXaoC-0006oZ-7x for ietf-http-wg@w3.org; Wed, 01 May 2013 17:27:13 +0000
Received: by mail-ob0-f180.google.com with SMTP id uk5so1483669obc.11 for <ietf-http-wg@w3.org>; Wed, 01 May 2013 10:26:46 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:mime-version:in-reply-to:references:from:date:message-id :subject:to:cc:content-type:content-transfer-encoding; bh=OKtRVmn+i0l/Jzqpq3RqD3okqFvJVjtRrWgZ2brocVo=; b=fLOL6TW1GTqHEDfutg/eQTx2YwwD9KpIgChB+Macdlf3fT2GzMCnnFzX0dfHm2M3KW vgMakk9HrWsFGKd8idiwN17/6Mwc27S8IWKS7iS/ziLFvpAoG8eeKLE22R7LM6i/Hghu 8ixyr4iAiVirRkywvqSQOwry5kvbPRtaDdOma5kdt7ySJTUVvPn3+ErMr9xosYEztgc0 P/jTwF275WlsGZeBBbm20snPatoycvWx4q/eBMe7TnL5v2da9Y+qRKvcPMfSMI/PqQXe Ubhys05ajRH3TOXWoZ5ZxzetsgvnH2AYO1eRQdMNXdAhzJ08BhV6Bu0Ga3jDENh3u38l k7gg==
X-Received: by 10.60.42.135 with SMTP id o7mr841408oel.97.1367429206299; Wed, 01 May 2013 10:26:46 -0700 (PDT)
MIME-Version: 1.0
Received: by 10.60.3.137 with HTTP; Wed, 1 May 2013 10:26:26 -0700 (PDT)
In-Reply-To: <CAA4WUYgAT64jj=Am06MsA02A+eAcDrVbbgb4opO37bnMkWTPfg@mail.gmail.com>
References: <CABP7RbdBe-Xkx+CMvpN=_oNAqm6SyLyL+XNHRUKSqn8mjSDw1Q@mail.gmail.com> <CAA4WUYgCiyWerT0tUUVKcbNPqdTGuXHd_MG59DjcUsEWst5t7g@mail.gmail.com> <CABkgnnVdU=cZ53Bqg5Un=E80NMpcgYO37DVmwUFW0O-i7SNf8w@mail.gmail.com> <CAA4WUYhz64FsEGgGhx91RfWwuPPxWdAkesOV-bmqWVWE7ZxdjA@mail.gmail.com> <CABP7RbcKQkn1o4WZscwNmSmm6YzqE_TKxPr4jnozNdaVqpZ7=A@mail.gmail.com> <CAA4WUYhF6rAZoYEaz4aJO6xawaJxzxGt=Bkg4H9eBOP-LBSRmQ@mail.gmail.com> <CAP+FsNezQzxdZEJY_2_0h_TR2pBbVsGyGBhQhKcm-65pt6S8rQ@mail.gmail.com> <CABP7RbevS8M0q9OxzPncqY_gE34q5-ymdg2hOX2SQgSUNkhzsw@mail.gmail.com> <CAA4WUYjAbuUqz9RdO+-p3a4EsyuS=Gv0rS-U-Vh+ZCjtDjFy6w@mail.gmail.com> <CAP+FsNec2LLZMjtGhSX-1q8qg66WtBoM5K0yMrs5m4VKXb5OVg@mail.gmail.com> <CAA4WUYgAT64jj=Am06MsA02A+eAcDrVbbgb4opO37bnMkWTPfg@mail.gmail.com>
From: James M Snell <jasnell@gmail.com>
Date: Wed, 01 May 2013 10:26:26 -0700
Message-ID: <CABP7Rbdgz=kRZPfjHK5UUfieq8uz=ToQZjFt1-+s9scj1CogmA@mail.gmail.com>
To: "William Chan (陈智昌)" <willchan@chromium.org>
Cc: Roberto Peon <grmocg@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>, Martin Thomson <martin.thomson@gmail.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Received-SPF: pass client-ip=209.85.214.180; envelope-from=jasnell@gmail.com; helo=mail-ob0-f180.google.com
X-W3C-Hub-Spam-Status: No, score=-3.5
X-W3C-Hub-Spam-Report: AWL=-2.700, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_LOW=-0.7, SPF_PASS=-0.001
X-W3C-Scan-Sig: lisa.w3.org 1UXaoC-0006oZ-7x ee54f23ea527108e1299376f241c1406
X-Original-To: ietf-http-wg@w3.org
Subject: Re: Design Issue: Max Concurrent Streams Limit and Unidirectional Streams
Archived-At: <http://www.w3.org/mid/CABP7Rbdgz=kRZPfjHK5UUfieq8uz=ToQZjFt1-+s9scj1CogmA@mail.gmail.com>
Resent-From: ietf-http-wg@w3.org
X-Mailing-List: <ietf-http-wg@w3.org> archive/latest/17764
X-Loop: ietf-http-wg@w3.org
Resent-Sender: ietf-http-wg-request@w3.org
Precedence: list
List-Id: <ietf-http-wg.w3.org>
List-Help: <http://www.w3.org/Mail/>
List-Post: <mailto:ietf-http-wg@w3.org>
List-Unsubscribe: <mailto:ietf-http-wg-request@w3.org?subject=unsubscribe>
Why not just bring the UNIDIRECTIONAL flag back as a PUSH_PROMISE frame-specific flag? If a PUSH_PROMISE frame has the unidirectional flag set, the stream is automatically half-closed in the return direction. If the flag is unset, the promised stream remains half-open until the client half-closes or a rst_stream is sent. On Mon, Apr 29, 2013 at 2:44 PM, William Chan (陈智昌) <willchan@chromium.org> wrote: > Remember we originally *had* a flag for UNIDIRECTIONAL, which we removed > because it was redundant in the traditional HTTP use cases. > > > On Mon, Apr 29, 2013 at 6:39 PM, Roberto Peon <grmocg@gmail.com> wrote: >> >> At worst, we burn a flag which states it is half-closed or unidirectional, >> or provide some other information which identifies the IANA port number for >> the overlayed protocol or something. >> Anyway, *shrug*. >> -=R >> >> >> On Mon, Apr 29, 2013 at 2:32 PM, William Chan (陈智昌) >> <willchan@chromium.org> wrote: >>> >>> On Mon, Apr 29, 2013 at 6:17 PM, James M Snell <jasnell@gmail.com> wrote: >>>> >>>> +1 on this. I like this approach. >>>> >>>> On Apr 29, 2013 2:15 PM, "Roberto Peon" <grmocg@gmail.com> wrote: >>>>> >>>>> I had thought to provide no explicit limit for PUSH_PROMISE, just as >>>>> there is no limit to the size of a webpage, or the number of links upon it. >>>>> The memory requirements for PUSH are similar or the same (push should >>>>> consume a single additional bit of overhead per url, when one considers that >>>>> the URL should be parsed, enqueued, etc.). >>>>> If the browser isn't done efficiently, or, the server is for some >>>>> unknown reason being stupid and attempting to DoS the browser with many >>>>> resources that it will never use, then the client sends RST_STREAM for the >>>>> ones it doesn't want, and makes a request on its own. all tidy. >>> >>> >>> I don't feel too strongly here. I do feel like this is more of an edge >>> case, possibly important for forward proxies (or reverse proxies speaking to >>> backends over a multiplexed channel like HTTP/2). It doesn't really matter >>> for my browser, so unless servers chime in and say they'd prefer a limit, >>> I'm fine with this. >>> >>>>> >>>>> As for PUSH'd streams, the easiest solution is likely to assume that >>>>> the stream starts out in a half-closed state. >>> >>> >>> I looked into our earlier email threads and indeed this is what we agreed >>> on (http://lists.w3.org/Archives/Public/ietf-http-wg/2013JanMar/1106.html). >>> I voiced some mild objection since if you view the HTTP/2 framing layer as a >>> transport for another application protocol, then bidirectional server >>> initiated streams might be nice. But in absence of any such protocol, this >>> is a nice simplification. >>> >>>>> >>>>> -=R >>>>> >>>>> >>>>> On Mon, Apr 29, 2013 at 12:33 PM, William Chan (陈智昌) >>>>> <willchan@chromium.org> wrote: >>>>>> >>>>>> On Mon, Apr 29, 2013 at 3:46 PM, James M Snell <jasnell@gmail.com> >>>>>> wrote: >>>>>>> >>>>>>> >>>>>>> On Apr 29, 2013 11:36 AM, "William Chan (陈智昌)" >>>>>>> <willchan@chromium.org> wrote: >>>>>>> > >>>>>>> [snip] >>>>>>> >>>>>>> > >>>>>>> > >>>>>>> > Oops, forgot about that. See, the issue with that is now we've made >>>>>>> > PUSH_PROMISE as potentially expensive as a HEADERS frame, since it does more >>>>>>> > than just simple stream id allocation. I guess it's not really a huge issue, >>>>>>> > since if it's used correctly (in the matter you described), then it >>>>>>> > shouldn't be too expensive. If clients attempt to abuse it, then servers >>>>>>> > should probably treat it in a similar manner as they treat people trying to >>>>>>> > abuse header compression in all other frames with the header block, and kill >>>>>>> > the connection accordingly. >>>>>>> > >>>>>>> >>>>>>> Not just "potentially" as expensive.. As soon as we get a push >>>>>>> promise we need to allocate state and hold onto it for an indefinite period >>>>>>> of time. We do not yet know exactly when that compression context can be let >>>>>>> go because it has not yet been bound to stream state. Do push streams all >>>>>>> share the same compression state? Do those share the same compression state >>>>>>> as the originating stream? The answers might be obvious but they haven't yet >>>>>>> been written down. >>>>>> >>>>>> >>>>>> I guess I don't see per-stream state as being that expensive. >>>>>> Compression contexts are a fixed state on a per-connection basis, meaning >>>>>> that additional streams don't add to that state. The main cost, as I see it, >>>>>> is the decompressed headers. I said potentially since that basically only >>>>>> means the URL (unless there are other headers important for caching due to >>>>>> Vary), and additional headers can come in the HEADERS frame. Also, >>>>>> PUSH_PROMISE doesn't require allocating other state, like backend/DB >>>>>> connections, if you only want to be able to handle (#MAX_CONCURRENT_STREAMs) >>>>>> of those backend connections in parallel. >>>>>> >>>>>> If they're not specified, then we should specify it, but I've always >>>>>> understood the header compression contexts to be directional and apply to >>>>>> all frames sending headers in a direction. Therefore there should be two >>>>>> compression contexts in a connection, one for header blocks being sent and >>>>>> one for header blocks being received. If this is controversial, let's fork a >>>>>> thread and discuss it. >>>>>> >>>>>>> >>>>>>> >> >>>>>>> >> >>>>>>> >> > As far as the potential problem above, the root problem is that >>>>>>> >> > when you >>>>>>> >> > have limits you can have hangs. We see this all the time today >>>>>>> >> > with browsers >>>>>>> >> > (it's only reason people do domain sharding so they can bypass >>>>>>> >> > limits). I'm >>>>>>> >> > not sure I see the value of introducing the new proposed limits. >>>>>>> >> > They don't >>>>>>> >> > solve the hangs, and I don't think the granularity addresses any >>>>>>> >> > of the >>>>>>> >> > costs in a finer grained manner. I'd like to hear clarification >>>>>>> >> > on what >>>>>>> >> > costs the new proposed limits will address. >>>>>>> >> >>>>>>> >> I don't believe that the proposal improves the situation enough >>>>>>> >> (or at >>>>>>> >> all) to justify the additional complexity. That's something that >>>>>>> >> you >>>>>>> >> need to assess for yourself. This proposal provides more granular >>>>>>> >> control, but it doesn't address the core problem, which is that >>>>>>> >> you >>>>>>> >> and I can only observe each other actions after some delay, which >>>>>>> >> means that we can't coordinate those actions perfectly. Nor can >>>>>>> >> be >>>>>>> >> build a perfect model of the other upon which to observe and act >>>>>>> >> upon. >>>>>>> >> The usual protocol issue. >>>>>>> > >>>>>>> > >>>>>>> > OK then. My proposal is to add a new limit for PUSH_PROMISE frames >>>>>>> > though, separately from the MAX_CONCURRENT_STREAMS limit, since PUSH_PROMISE >>>>>>> > exists as a promise to create a stream, explicitly so we don't have to count >>>>>>> > it toward the existing MAX_CONCURRENT_STREAMS limit (I searched the spec and >>>>>>> > this seems to be inadequately specced). Roberto and I discussed that before >>>>>>> > and may have written an email somewhere in spdy-dev@, but I don't think >>>>>>> > we've ever raised it here. >>>>>>> > >>>>>>> >>>>>>> Well, there is an issue tracking it in the github repo now, at >>>>>>> least. As currently defined in the spec, it definitely needs to be >>>>>>> addressed. >>>>>> >>>>>> Great. You guys are way better than I am about tracking all known >>>>>> issues. I just have it mapped fuzzily in my head :) >>>>> >>>>> >>> >> >
- Design Issue: Max Concurrent Streams Limit and Un… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Poul-Henning Kamp
- RE: Design Issue: Max Concurrent Streams Limit an… RUELLAN Herve
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… Roberto Peon
- Re: Design Issue: Max Concurrent Streams Limit an… William Chan (陈智昌)
- Re: Design Issue: Max Concurrent Streams Limit an… James M Snell
- Re: Design Issue: Max Concurrent Streams Limit an… Martin Thomson