Your Node.js API Was Fast. Now It's Slow. Here's How to Diagnose It.

The article you've shared provides a comprehensive guide for diagnosing and addressing performance issues in Node.js applications. Here are the key takeaways:

Key Points

1. Event Loop Delay Measurement:

   • Use perf_hooks.monitorEventLoopDelay to monitor event loop delays.
   • This helps rule out blocking code that might be causing performance degradation.

2. Connection Pool Wait Count:

   • Check the connection pool wait count using tools like clinic flame.
   • High wait counts indicate potential database exhaustion, which can cause latency issues.

3. Heap Growth Monitoring:

   • Monitor heap growth over a period (e.g., 30 minutes) to identify memory leaks or GC pressure.
   • Common sources of memory leaks include event listeners not cleaned up, closures holding references, unbounded caches, and global state accumulation.

4. CPU Profiling with Clinic Flame:

   • Use clinic flame under load to identify CPU hotspots.
   • This helps pinpoint specific areas in the code that are consuming excessive resources.

5. Dependency Changes Review:

   • Check recent dependency changes using git log -- package-lock.json.
   • Sometimes, updates to dependencies can introduce performance issues or

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