Depends, in a very low loss environments and with nagle turned off probably less than 2% difference in latency. I find in 90% of cases people who use UDP end up writing 70 or 80 % of the TCP stack eg piggy backing packets , windowing and acks and end up with similar performance. In a low to medium loss environment you can get some benefits by removing the worst case and loss by spamming multiple udp packets ( you can get a order of magnitude improvement in worst case performance) but then again firewalls are an issue.. Also note most routers will drop UDP packets before TCP when they are under stress.
>The overall end-to-end latency between a zmq_msg_send() in one application on one host and zmq_msg_recv() in another application on the same host over the loopback interface is just too high for what we need UDP on the wire will not be better than any system using a tcp loop-back. I suggest your requirement may not be feasible. A congested environment is far more of a latency issue then TCP/UDP and you would almost certainly be better of adding a few NICs just for the high performance channel ( cheaper too) . Note never measure the latency of the first packet on tcp a lot of setting up is done. Ben On Wed, Nov 28, 2012 at 6:25 AM, Dan Goes <[email protected]> wrote: > _send() in one application on one host and zmq_msg_recv() in another > application on the same host over the loopback interface is just too high > for what we need. Initial profiling suggests that a non-negligible amount > of that latency is bound up in zeromq and networking land. Is it possible > to take a swing at how significant a decrease we would see in this latency > by using UDP instead? I.e., are we talking an order of magnitude, or more > like 5-10%? Ultimately, we'll have messages sent inter-host instead of > intra-host, and our environment is not inherently lossy, but possibly > congested. That is, a lot of small messages are going out frequently, but > the total throughput experienced by the network is unlikely to be high. The > drawbacks of U
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