Cómo Diagnosticar y Solucionar Memory Leaks en Aplicaciones Node.js

Detecting and resolving memory leaks is essential in applications developed with Node.js due to the environment's memory limit (by default, 2 GB). A memory leak occurs when a program accumulates memory continuously without freeing it, causing an exaggerated growth of consumption, which eventually causes the application to fail.

What is a memory leak in Node.js?

A memory leak occurs when a program accumulates memory without freeing it at any time. The problem arises when exceeding the predetermined heap capacity (allocated memory), causing the application to stop due to lack of available memory.

The maximum heap memory in Node.js is generally 2 GB, which means that a bad memory management can cause our process to fail irreversibly when exceeding this barrier.

How to diagnose a memory leak?

To identify memory leaks, it is crucial to constantly monitor the memory used by our application, especially under significant loads. To do so, we can follow the following practical steps:

• Create regular metrics using functions such as process.memoryUsage().
• Use tools such as autocanon to simulate heavy loads on our endpoints and detect persistent memory spikes.
• Monitor applications in real time using tools such as Solid, observing the evolution of parameters such as:
• Total Heap usage.
• Current memory usage.
• Frequency and effectiveness of the garbage collector (GC).

What techniques exist to identify problematic memory areas?

A prominent technique for further analysis is the capture and evaluation of a heap snapshot, i.e., a snapshot of the current memory state that can be analyzed with Chrome Developer Tools or similar tools. The essential steps involve:

• Capture multiple snapshots at different intervals or situations.
• Compare those snapshots to identify objects that grow in retained memory size.
• Analyze retained size to discover persistent references to unnecessary objects, which may be generating the memory leak.

What was the practical example of the memory leak?

In the practical exercise shown, we detected how storing a function that directly references the request object in an array keeps unnecessary objects in memory.

By permanently storing these functions in an array generated with:

const listener  = (data)  => console.log('event received:', data.url);listeners.push(listener);emitter.on('Data', listener);

Each request preserves references that should be freed, causing an unnecessary and growing backlog in memory. This happens specifically by retaining the entire request object, which could be collected once each request is completed.

How can we solve this problem in our applications?

The effective solution is to avoid unnecessarily retaining references to objects with short life cycles, such as request objects. By replacing these references with simple or isolated values, we will avoid excessive memory retention.

For example, by avoiding directly retaining the URL of the original request object within long-lived arrays:

emitter.emit('Data',  { message: 'hello' });

By performing this simple modification, we manage to stop the unwanted memory increase.

Do you have any experience detecting memory leaks in Node.js? Share your learning and doubts in the comments!