Maximum number of node.js processes in cluster mode

Question

Why all examples of cluster mode in node.js forks to number of processes that equals number of CPUs?

var cluster = require('cluster'); var numCPUs = require('os').cpus().length;  if (cluster.isMaster) {     // Fork workers.     for (var i = 0; i < numCPUs; i++) {         cluster.fork();     }      cluster.on('exit', function(worker, code, signal) {         console.log('worker ' + worker.process.pid + ' died');     }); } else {     // worker process     // do the job.... } 

Is it possible to fork to higher number of processes? I've tried this code with 10 processes on core-4 and it seems to be working. But- is it a good idea?

Answer 1

The reason why the number of forks equals the number of CPU cores, is because that is the optimal number. Increasing it past that, can decrease performance, reason being is that since if your processor has N number of cores, it can only process N number of processes at the same time.

For example: if you have 4 cores, and you have 10 processes where each process will have at minimum 1 thread, only 4 of these threads can ever be executed by your CPU concurrently. The rest of the threads will be waiting for their turn to be executed by the processor. Your OS will then intermittently perform a context switch , whereby it will pause a running thread, and switch to a thread that is waiting, and execute that thread instead. This "switching" process results in additional processing overhead. Therefore, for the most efficient use of your CPU cycles, you want the number of your forks (processes) to match the number of your cores in order to minimize context switches.