Currently, proxy.config.spdy.initial_window_size_in is set to the default value 64K (suggested in
http://www.chromium.org/spdy/spdy-protocol/spdy-protocol-draft3-1). This suggested value is perhaps due to historic reasons when the window_size was only allowed 2 octets in the older spdy versions.
Note that, ideally, the client (sender) should still be able to defer the upload when the send window is exhausted until the server (receiver) sends an WINDOW_UPDATE frame indicating to resume the sending.
Even so, 64K may still be too small and may result in increasing upload
latencies, especially, in case of large concurrent upload scenarios. Hence, I would like to bump up the default value for the spdy initial window
size to a higher value (preferably to 1 mb like some of the more popular spdy enabled web servers are using).
Here's some basic benchmarking data (thanks to yzlai):
5 parallel uploads from APAC to the US with a total of 2,299,250 bytes.
spdy=off, 2.34 secs
spdy=on, spdy.initial_window_size_in=64k: 11.28 secs
spdy=on, spdy.initial_window_size_in=1M: 1.99 secs
spdy=on, spdy.initial_window_size_in=10M: 2.01 secs