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RE: Massive HTTP/2 parallel requests

From: Lucas Pardue <>
Date: Mon, 14 Mar 2016 14:04:07 +0000

Molina wrote:

> You can find it here:

Thanks for the link and the background investigation and information, this is really interesting.

> Yes, I think I can drop some light on this issue. If you take a look at the last message of the chain [4] it can be seen that the distance between server and client is so big that, as you mentioned, the client does not send on time the WINDOW_UPDATE request. But why? The client sends it when it’s current window is at half of its capacity, which is suddenly filled when it receives packages from the server. The problem is that the server does not receive this message on time either, so it doesn’t send any more packages while this request is arriving.

Daniel Stenberg wrote:

> We need to promise a big enough HTTP/2 window that allows the other end to send at full speed and for us to send back window updates in due time. I wonder if we could make so that we get some RTT timing back from nghttp2 and we could use that as input for how large window to set... Or perhaps we could even make such a window scaling option into nghttp2 itself.

So it sounds like the overall throughput is governed by half the maximum window size. I like the sound of an auto scaling window, you could PING (frame) the server early in the connection and use that as an early indicator of RTT and scale up window size in some manner. Or you could be more aggressive with sending WINDOW_UPDATES e.g. after every frame received.


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Received on 2016-03-14