How to understand that there is a problem in the event loop?

Application slowdown or hang, increased latency when processing requests.

High CPU load, often close to 100%, without intensive computations.

Constant increase in RAM usage not related to data growth (memory leaks).

Failure of scheduled operations (e.g., timers) or their execution with significant delay.

Errors like "Event loop is locking up" or similar warnings in logs.

Using monitoring tools that show prolonged blocking of the Event Loop:

• Node.js core modules: process.hrtime.bigint() for measuring code execution.
• Profilers: node --prof for collecting performance data.
• Libraries for monitoring Event Loop: blocked, eventemitter2 (in debug mode).

// Example of using blocked to detect lockups
const blocked = require('blocked');

blocked((ms) => {
  console.warn(`Event loop blocked for ${ms}ms`);
});

// Simulating a blocking operation
function sleep(ms) {
  const start = process.hrtime.bigint();
  while (process.hrtime.bigint() - start < BigInt(ms * 1e6)) {
    // Blocking loop
  }
}

sleep(100); // Will trigger a warning