Re: Overhead of HTTP/2 Stream Management.

[Roberto Peon <[e-mail]>]

If that is true, then you may want to write up a server and client
implementation, test/deploy it in the real world, and the write up.submit a
draft.
-=R

On Sun, Apr 5, 2015 at 4:37 PM, Max Bruce <[e-mail]> wrote:

> Well, I proposed a HTTP/1.1 addition to Mark, that prevents HOL blocking &
> allows server pushing in HTTP/1.1, with 100% backwards compatibility, and
> relative ease to implement, and can even start HPACK without any direct
> protocol negotiations. TCP is in charge of ensuring that content gets where
> it needs to go, if that TCP is untimely closed, that's something the client
> just has to re-request. As for the connection/stream overhead, you can have
> only one case of initializing TCP, and zero stream overhead, using 1-2 HTTP
> headers, that allow server pushing and prevent HOL blocking if implemented
> on both client and server(and if not, prepare the responses for the client
> before they ask).
>
> On Sun, Apr 5, 2015 at 4:15 PM, Greg Wilkins <[e-mail]> wrote:
>
>>
>> Max,
>>
>> I don't see much difference between the stream overheads of HTTP/2 vs the
>> connection overheads of HTTP/1.
>>
>> Both need open/close state kept and even in HTTP/1 that state is
>> moderately complex as you can be half closed in and/or half closed out; the
>> response can complete before the request; there are multiple sources of
>> events (application vs network) that can race on state changes; the server
>> has a requirement to reliably deliver a serialised event stream to the
>> application without duplicates or loopbacks.    Unless the server/client
>> keeps good atomic state on the open/closed status, then there are going to
>> be lost events and/or leaked resources.
>>
>> In jetty the vast majority of this state overhead is in common code used
>> by both HTTP/1 and HTTP/2.    This code used to be a lot simpler in older
>> versions of our HTTP/1 on server... but it was wrong code that missed many
>> edge cases when presented with fully asynchronous applications.   Closing
>> asynchronous streams is just complex and multiplexing changes that very
>> little. It just makes the network event stream look a little different and
>> some events are distributed to multiple listeners.
>>
>> cheers
>>
>>
>> On 6 April 2015 at 06:08, Max Bruce <[e-mail]> wrote:
>>
>>> The way HTTP works though, we don't need streams in such a conventional
>>> and TCP-like way. We only need multiplexed packets to carry data over, so
>>> just associate request/response pairs with an ID, and allow server push via
>>> server sending the request path in a header too. Why do we even need a
>>> frame structure? It's unnecessary overhead. Same with the virtual streams.
>>>
>>> On Sun, Apr 5, 2015 at 11:57 AM, Willy Tarreau <[e-mail]> wrote:
>>>
>>>> On Sun, Apr 05, 2015 at 11:45:53AM -0700, Max Bruce wrote:
>>>> > My thoughts is that you just don't use so much overhead. You don't
>>>> get rid
>>>> > of stream IDs, you just don't need so much complex things surrounding
>>>> it.
>>>> > Example: You append a header to HTTP/1.1 request, with a response ID,
>>>> > server responds with it. Server can push responses by sending a
>>>> unsent ID &
>>>> > request path in a header.
>>>>
>>>> You still need the stream IDs in the frames themselves so that you know
>>>> which stream each frame belongs to.
>>>>
>>>> Multiplexed systems always look simple at first, until you start to
>>>> implement them, cover the corner cases (eg: who closes first etc) and
>>>> you finally realize once everything is done how much your system looks
>>>> like tcp...
>>>>
>>>> There was an elegant (in my opinion) simplification in H/2 compared to
>>>> other systems, the stream IDs are always incremented until the largest
>>>> encodable ID is reached, which is where a new connection must be used.
>>>> I find this elegant because you don't need to keep track of IDs in use
>>>> vs available ones and it really simplifies a number of things (eg: no
>>>> risk to have late frames from an old stream using the same ID).
>>>>
>>>> It doesn't please me either to have to implement such a complex system
>>>> but I am absolutely convinced that it can hardly be simplified further
>>>> as long as we want non-blocking, multiplexed streams. I have already
>>>> implemented multiplexed streams in the past for some projects, and it
>>>> resulted in almost the same design (but more complex).
>>>>
>>>> Willy
>>>>
>>>>
>>>
>>
>>
>> --
>> Greg Wilkins <[e-mail]>  @  Webtide - *an Intalio subsidiary*
>> http://eclipse.org/jetty HTTP, SPDY, Websocket server and client that
>> scales
>> http://www.webtide.com  advice and support for jetty and cometd.
>>
>
>