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node.jslibuv

Details of how Node JS works?

I want to ask some clarifying questions about NodeJS, which I think are poorly described on the resources I studied.

Many sources say that NodeJS is not suitable for complex calculations, because it is single-threaded and queries are executed sequentially

I created the simplest server on Node and wrote an endpoint that executes a request for about 10 seconds (a cycle). Next, I made 10 consecutive requests via Postman, and indeed, each subsequent request began execution only after the previous one gave a response.

  1. Do I understand correctly that in this case, if the execution time of one endpoint is approximately 300ms, and 700 users will access the server at the same time, then the waiting time for the last user will be a critical 210,000 ms?

  2. I also heard that the advantage of NodeJS is the ability to support a large number of simultaneous connections, then what does this mean and why is it a plus if the answer for the last person from the last question will still be very long

  3. Another statement I came across is that libuv allows you to do many I/O operations at the same time, how does it work if NodeJS processes requests sequentially anyway?

Thank you very much!

Solution

  • TL;DR: I/O operations don't block the single execution thread. CPU intensive tasks DO block the thread and a NodeJS web server is not a good option in that case.

    1. Yes, if your endpoint needs 300ms of synchronous work (cpu) to complete the operation, the last user will wait 210,000ms.
    2. NodeJS is good at handling a large number of connections when the work it needs to do is i/o bound. It is not a good choice if the endpoint needs a lot of CPU time.
    3. I/O operations operate at a different layer and take ZERO CPU time. That means that once the I/O operation is fired, NodeJS can accept new calls to the endpoint. NodeJS then polls the Operating System for completed I/O calls whenever its not using CPU and executes the callbacks. This is what allows it to handle a large number of concurrent requests without one user needing to wait for others to finish.