It seems to me it's not because the Node.js test used a remote machine to drive the connections whereas this one is driving the connections from the same machin

It seems to me it's not because the Node.js test used a remote machine to drive the connections whereas this one is driving the connections from the same machine. Running the server and test harness on the same machine bypasses a whole lot of networking stack. Also, it seems the limitation in Node.js is the maximum heap size of around 1.4GB [1]. This test used a heap size of 3GB which is just not possible in Node (until the limitation is removed, anyway). [1]: http://blog.caustik.com/2012/04/10/node-js-w250k-concurrent-connections/ http://blog.caustik.com/2012/04/10/node-js-w250k-concurrent-...