On 31/07/2012 3:20 AM, Oz Linden (Scott Lawrence) wrote: > On 2012-07-29 13:58 , Sheet Spotter wrote: >> Does increasing the HTTP connection limit also increase the burden on the >> server and network? >> >> Increasing the HTTP connection limit on one client might improve the >> experience for one person. It might also diminish the experience for >> everyone else on the same server. > Exactly so. The effect is more complex than just consuming file > descriptors on the server side, as well. TCP congestion control works > far better when dealing with a smaller number of connections. Any > packets that are not subject to congestion control that are sharing the > same network path as a TCP connection increase the likelihood of a > dropped packet in the connection flow, which causes the connection to > immediately cut its transmission window by half. The viewer already puts > a lot of UDP traffic into the same path. The handshake packets that open > and close TCP connections are also not subject to the congestion control > - which means that opening each new connection increases the chances > that each of your existing connections will slow down by half. Opening > many connections also puts additional strain on routers in the path that > are doing connection tracking (which too many do), adding another > possible source of problems. > > In general, when persistent connections and pipelined requests (having > more than one request in flight on a connection at a time) are used, > HTTP performs far better with a small number of connections than with > more. As we begin deploying support for this way of using it on the > server side, we'll be able to do good experiments to determine what the > right tradeoffs are for network behavior and server load to provide > optimal experience for users. > > Also, a badly behaving connection (eg: one that is dropping packets) leaves the connection open longer, while delivering less data per unit time. That's basically a *waste* of server resources. If I overload my crappy consumer router with connections it can't properly handle, I'm indirectly impacting the experience of other users. Not a desirable situation.
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