Network I/O- The Underhood of Node.js
By Rajesh krishnakumar — “Go above and beyond!”
Does Node Js use libuv Thread Pool for Network I/O?
Everyone is confused that network request from node application is handled by event loop or libuv (ThreadPool).
Interviewed multiple candidates but many of them were confused about it. Let’s clear the confusion
Let’s discuss a few technical words that always come across with node js
libuv is a C library originally written for Node.js to abstract non-blocking I/O operations, Lifting all the heavy jobs.
Libuv assigns tasks to a pool of worker threads. However, all call-backs that occur on task completion are executed on the main thread.
By default size of UV_THREADPOOL_SIZE is 4.
Let us all assume that network call is blocking operation so event loop sent to thread pool do the task.
Yes, you are right but here is the catch if a request is called with the hostname then *dns.lookup()* is used so it go-to thread pool, If you called by IP or doing a lookup by yourself then dns.lookup is avoided and we can make thread pool free for another job.
Most of us call API by hostname in the node server so that means if you do >4 DNS lookups in parallel then you’re going to block the libuv thread pool.
In node js DNS.lookup() calls getaddrinfo(), a function in the system resolver library that makes blocking socket calls and cannot be integrated into the polling loop, like fs* it’s called in the thread pool. Everything else is async in DNS except DNS.lookup.
Let’s say you have 100 concurrent connections everything started using thread pool it will degrade the performance, either you need to increase the thread pool or add more CPU or come out of thread pool.
Note: It doesn’t block the main thread.
Try to resolve the DNS yourself on event loop or use proxy DNS caching or calling by IP
Various networking APIs will call
dns.lookup() internally to resolve host names. If that is an issue, consider resolving the hostname to an address using
dns.resolve() and using the address instead of a hostname. Also, some networking APIs (such as
dgram.createSocket()) allow the default resolver,
dns.lookup()to be replaced.
Npm package for cacheable DNS cacheable-lookup
OS level you can refer to this article
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