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From Andreas Veithen <andreas.veit...@gmail.com>
Subject Re: HTTP Core Performance and Reactor Buffer Size
Date Sun, 24 Nov 2013 18:00:07 GMT
On Sun, Nov 24, 2013 at 5:40 PM, Andreas Veithen
<andreas.veithen@gmail.com> wrote:
> What I still don't understand completely is why this causes such a
> slowdown. The effect of the issue in httpcore-nio is that the peer
> sees the TCP window size gradually drop from 43690 to 8192. Would that
> trigger some mechanism in the TCP stack of the peer that delays the
> transmission of TCP segments (even if the window is not 0)?

After reviewing some aspects of TCP, I think that the most likely
candidate to explain this behavior is actually the "silly window
syndrome" avoidance algorithm. Since the problem occurs in an
integration test, all communication goes over the loopback interface
where MSS=65495. This means that the window size gets much smaller
than both the MSS and the initial/maximum window size. Probably Linux
considers this as "silly" small and starts delaying transmission in an
attempt to allow the window to grow to a more reasonable size (which
of course never happens).


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