How do I know if increasing the thread pool size helped?
Monitor response times, CPU usage, and event loop lag before and after the change. If performance improves, keep it. If it does not or CPU is saturated, revert. Always measure; do not guess when tuning performance.
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More FAQs in How to Tune the Thread Pool Size in Node.js for Performance
Set UV_THREADPOOL_SIZE in the environment before starting Node.js. The default is 4. Increase it if your app does many concurrent fs, DNS, or crypto operations. Monitor CPU usage and event loop lag after changing.
When your app does many concurrent file system operations, DNS lookups, or crypto operations, and the default 4 threads are a bottleneck. Monitor to confirm the bottleneck is in thread-pool operations, not elsewhere.
No. Network I/O does not use the thread pool; it uses the OS's async capabilities directly. Increasing the pool size only helps for fs, DNS, and crypto operations that use the thread pool.
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