Re: Design Issue: Max Concurrent Streams Limit and Unidirectional Streams
James M Snell <jasnell@gmail.com> Mon, 29 April 2013 21:18 UTC
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Date: Mon, 29 Apr 2013 14:17:36 -0700
Message-ID: <CABP7RbevS8M0q9OxzPncqY_gE34q5-ymdg2hOX2SQgSUNkhzsw@mail.gmail.com>
From: James M Snell <jasnell@gmail.com>
To: Roberto Peon <grmocg@gmail.com>
Cc: "ChanWilliam(陈智昌)" <willchan@chromium.org>, 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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+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. > > As for PUSH'd streams, the easiest solution is likely to assume that the > stream starts out in a half-closed state. > -=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