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#event-loop

2 stories

Programming Languages Bug Report

Health checks timed out during report exports: CPU work blocked the Node.js event loop

Lucas Moreau · Jun 29, 2025 · 8 min read

Whenever someone exported a large CSV report, our Node.js API stopped answering everything else, including liveness probes, and pods restarted mid-export. Building 200,000 rows synchronously blocked the event loop for seconds. How we measured it and moved the work off the main thread.

Banner: Node.js event loop phases with timers, check and microtask queues racing in different orders

Programming Languages Bug Report

Flaky Node.js ordering: setTimeout 0 vs setImmediate vs process.nextTick

John Nguyen · Dec 19, 2024 · 8 min read

A batching test in our Node.js telemetry library failed about one run in twenty on CI and never locally. The code assumed setTimeout 0 fires before setImmediate, which Node does not guarantee in the main module. Moving to ESM later flipped nextTick and promise order too.