Scalability, latency, and throughput are key performance indicators for web servers. Keeping the latency low and the throughput high while scaling up and out is not easy. Node.js is a JavaScript runtime environment that achieves low latency and high throughput by taking a “non-blocking” approach to serving requests. In other words, Node.js wastes no time or resources on waiting for I/O requests to return.
In the traditional approach to creating web servers, for each incoming request or connection the server spawns a new thread of execution or even forks a new process to handle the request and send a response. Conceptually, this makes perfect sense, but in practice it incurs a great deal of overhead.
While spawning threads incurs less memory and CPU overhead than forking processes, it can still be inefficient. The presence of a large number of threads can cause a heavily loaded system to spend precious cycles on thread scheduling and context switching, which adds latency and imposes limits on scalability and throughput.
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