HTTP/2 Concurrent streams question

Simone Bordet simone.bordet at
Wed Nov 7 12:00:25 UTC 2018


On Wed, Nov 7, 2018 at 11:44 AM Michael McMahon
<michael.x.mcmahon at> wrote:
> Hi,
> This is the right place to ask! It was implemented that way because RFC 7540
> recommends that:
>    Clients SHOULD NOT open more than one HTTP/2 connection to a given
>    host and port pair, where the host is derived from a URI, a selected
>    alternative service [ALT-SVC], or a configured proxy.
> One workaround would be to create a second HttpClient in that situation.

>From the Jetty experience in the field, opening just one connection is
most often impractical.

The first reason is that the typical session flow control window will
be (almost) immediately exhausted and you get a large performance hit
due to the flow control frames roundtrips.
The second reason is that even enlarging the session flow control
window to very large values, you then end up hitting TCP flow control,
with the same effects on performance.

Opening few connections (many many less that you would with HTTP/1.1)
showed to be a good compromise between resource utilization and
performance (and outperforms HTTP/1.1).

Simone Bordet
Finally, no matter how good the architecture and design are,
to deliver bug-free software with optimal performance and reliability,
the implementation technique must be flawless.   Victoria Livschitz

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