Introduction to gc-stats

The gc-stats module is a powerful tool for monitoring and generating statistics about garbage collection (GC) in a Node.js application. Tracking these statistics can help developers fine-tune performance, trace memory issues, and understand how their applications behave under various loads. In this guide, we will introduce a number of useful gc-stats APIs and provide code snippets to demonstrate their usage.

Basic Usage

To get started with gc-stats, you first need to install it:

  npm install gc-stats

Once installed, you can require the module in your application:

  const gcStats = require('gc-stats')();

Listening to GC Events

The primary functionality of gc-stats is to provide insights by emitting events every time a garbage collection cycle occurs:

  gcStats.on('stats', (stats) => {
      console.log(`GC Type: ${stats.gctype},
                   Duration: ${stats.pauseMS},
                   Total Memory: ${stats.after.totalHeapSize}`);
  });

Detailed GC Information

Each event emitted contains detailed information about the garbage collection process:

• gctype: Type of garbage collection (Minor, Major, etc.)
• pauseMS: Duration of the pause in milliseconds
• before/after: Heap statistics before and after GC

  gcStats.on('stats', (stats) => {
      console.log(`GC Details:
                     Type: ${stats.gctype},
                     Pause: ${stats.pauseMS}ms,
                     Memory Used Before: ${stats.before.usedHeapSize} bytes,
                     Memory Used After: ${stats.after.usedHeapSize} bytes
                 `);
  });

Integrating with an Application

Here is an example of integrating gc-stats into a Node.js application:

  const http = require('http');
  const gcStats = require('gc-stats')();

  http.createServer((req, res) => {
    let memoryUsage = process.memoryUsage();

    gcStats.on('stats', (stats) => {
        console.log(`GC Event:
                       Type: ${stats.gctype},
                       Pause: ${stats.pauseMS}ms,
                       Heap Used Before: ${stats.before.usedHeapSize},
                       Heap Used After: ${stats.after.usedHeapSize}`);
    });

    res.writeHead(200);
    res.end(`Heap Used: ${memoryUsage.heapUsed}\n`);
  }).listen(8080);

  console.log('Server running on port 8080');

Conclusion

The gc-stats module is an essential tool for Node.js developers aiming to optimize their applications and monitor memory consumption. By utilizing its event-driven architecture, you can proactively track garbage collection events and react accordingly to ensure the best performance of your application.

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