Performance Profiling & Memory Leaks - Inspecting V8 Heaps & Event Loop Lag

Because Node.js servers run continuously for months without restarting, even a tiny memory leak of 500 KB per hour will eventually exhaust V8's default memory ceiling (~1.4 GB on 64-bit systems), causing a catastrophic process crash (FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory).

Programmatic Heap Snapshot Generation

// memoryProfiler.js
const v8 = require('v8');
const path = require('path');

function takeHeapSnapshot() {
  const fileName = path.join(process.cwd(), `snapshot-${Date.now()}.heapsnapshot`);
  const snapshotPath = v8.writeHeapSnapshot(fileName);
  console.log('[HEAP SNAPSHOT WRITTEN]:', snapshotPath);
}

// Take snapshot if memory exceeds threshold
setInterval(() => {
  const memory = process.memoryUsage();
  const heapUsedMB = memory.heapUsed / 1024 / 1024;

  if (heapUsedMB > 500) { // If heap exceeds 500 MB
    console.warn(`[WARNING] High Heap Usage: ${heapUsedMB.toFixed(2)} MB. Generating snapshot...`);
    takeHeapSnapshot();
  }
}, 30000);

Monitoring Event Loop Delay with perf_hooks

const { monitorEventLoopDelay } = require('perf_hooks');

// Monitor event loop delay histogram with 20ms resolution
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();

setInterval(() => {
  console.log({
    minDelayMs: (h.min / 1e6).toFixed(2),
    maxDelayMs: (h.max / 1e6).toFixed(2),
    meanDelayMs: (h.mean / 1e6).toFixed(2),
    p99DelayMs: (h.percentile(99) / 1e6).toFixed(2)
  });
  h.reset();
}, 5000);