Re: Design Issue: Max Concurrent Streams Limit and Unidirectional Streams
Roberto Peon <grmocg@gmail.com> Mon, 29 April 2013 21:40 UTC
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Date: Mon, 29 Apr 2013 14:39:39 -0700
Message-ID: <CAP+FsNec2LLZMjtGhSX-1q8qg66WtBoM5K0yMrs5m4VKXb5OVg@mail.gmail.com>
From: Roberto Peon <grmocg@gmail.com>
To: "William Chan (陈智昌)" <willchan@chromium.org>
Cc: James M Snell <jasnell@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>, Martin Thomson <martin.thomson@gmail.com>
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Subject: Re: Design Issue: Max Concurrent Streams Limit and Unidirectional Streams
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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