Why is the main thread the most important in Node.js?
Because it is where your JavaScript code runs and the event loop processes callbacks. Blocking the main thread with sync code or CPU-heavy work stops all requests, making it the biggest performance concern in Node.js.
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More FAQs in Node.js Performance and Threading Explained: Single Thread, Thread Pool, and Workers
Three concepts: the single main thread (where JavaScript runs and the event loop processes callbacks), the libuv thread pool (4 default threads for I/O that cannot be async), and worker threads (your threads for CPU-heavy work).
The main thread runs your code and the event loop. fs.readFile operations go to the thread pool if needed, with callbacks running on the main thread. For CPU-heavy computation, you create worker threads to offload work from the main thread.
For fs-heavy, DNS, or crypto-heavy apps where the 4 default thread pool threads can bottleneck. Tune UV_THREADPOOL_SIZE. For network-I/O-heavy apps, the thread pool does not matter, since network I/O uses the OS's async capabilities directly.
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