Understanding Memory Leaks in Software Development: How to Identify, Debug, and Prevent Them

At adagger, we’ve encountered and resolved several instances of memory leaks, most notably during a migration from Vue2 to Vue3, where a memory leak surfaced while using Server-Side Rendering (SSR). In this post, we’ll explain what memory leaks are, how to identify and debug them, and how to prevent them in the future.

What is a Memory Leak?

A memory leak occurs when an application unintentionally holds onto memory that it no longer needs. This memory is not freed up for reuse, leading to inefficient resource usage. Over time, the unclaimed memory accumulates, potentially causing the application to slow down or even crash.

In JavaScript-based applications, especially in single-page applications (SPAs) and server-side rendering (SSR) setups, memory leaks can occur if objects, event listeners, or other resources are not properly cleaned up when they are no longer needed.

How to Identify a Memory Leak

Detecting a memory leak can be challenging, but some common symptoms include:

1. Increased Memory Usage Over Time: If the application's memory usage keeps increasing with no significant drop or garbage collection, it's a sign of a possible memory leak.
2. Application Performance Degradation: Gradual performance degradation such as increased load times or UI slowdowns can be linked to poor memory management.
3. Frequent Crashes or Freezes: When an application consumes all available memory, it can cause crashes, especially in environments with limited resources, such as mobile devices or low-powered servers.
4. Out of Memory (OOM) Errors: On the server-side, particularly in SSR, you may encounter “out of memory” errors in the logs, signaling that the application is unable to reclaim unused memory.

In our most recent case, when we were approached by a client to investigate a memory leak that surfaced after the client's frontend was migrated from vue2 to vue3, there were multiple 503 status codes logged in the cloud run instance of the web frontend with the following error message:

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory

When looking at the container memory utilisation chart a jump in memory allocation became obvious after the deployment of the migrated version.

Tools for Identifying Memory Leaks

Fortunately, several tools exist to help developers identify and track down memory leaks. Some of the most common include:

• Chrome DevTools: For frontend applications, Chrome’s Developer Tools offer a heap snapshot feature that allows you to observe memory allocations and identify retained objects.
• Node.js --inspect flag: For server-side or SSR applications, Node.js has built-in memory profiling tools that can be accessed by running Node with the --inspect flag.
• Performance Monitoring Tools: Tools like New Relic, Datadog, or Sentry can also be configured to track memory usage in both frontend and backend environments.

Debugging Memory Leaks: Our Experience Migrating from Vue2 to Vue3

At adagger, we encountered an interesting memory leak issue after a web frontend was migrated from Vue2 to Vue3 with Server-Side Rendering (SSR) using nuxt. Here’s how we debugged and resolved it.

Step-by-Step Debugging Process

1. Build the application locally

Since the memory leak occurred in the production environment, ideally the production build is used to debug the memory consumption. There might be subtle differences between dev and prod builts which might distract when debugging a memory leak. Hence try to run the production build locally. The frontend that was affected was built on top of nuxt3 using the vuetify UI library. The build was created via:

npm run build

2. Run the app locally using Chrome DevTools

Using the --inspect flag in Node.js, we connected to the SSR server via Chrome DevTools.

node --inspect .output/server/index.mjs

This allowed us to take heap snapshots and compare them over time. In these snapshots, we noticed that components and certain instances of data were being retained even after they were no longer in use.

3. Use the frontend

When using the application, the memory usage might either stay constant over time (ideal) or increase significantly over time. In our case it was sufficient to refresh the pages via F5 to create requests which blocked additional memory on every request. However, you might also consider using a software to automatically send requests against your application, similar to a load test.

We then iteratively removed component from the page, re-built the application and again sent requests. Typically at some point memory usage stabilises and then you know which component is the culprit. Another option to identify the problematic component is to take a heap snapshot before sending requests and then again another one after sending multiple requests. Chrome dev tools allow you to drill down the diff in memory allocation and by looking at the objects in memory you might be able to identify which element causes the memory leak.

4. Check github for potential memory-related issues or fixes

Chances are you are not the only one affected by a specific memory issue. It might help to check relevant github repos for memory-leak related issues and potential fixes.

Best Practices to Prevent Memory Leaks

While our Vue migration experience highlighted how memory leaks can crop up in unexpected ways, there are some general best practices that can help you avoid these issues in your projects:

1. Proper Component Cleanup: In frameworks like Vue, React, and Angular, ensure that components are properly unmounted and destroyed when no longer needed. This is particularly important in SSR environments where components might persist across multiple requests.
2. Avoid Global Variables: Avoid keeping large objects or arrays in global scope, as they can easily be overlooked by the garbage collector.
3. Clean Up Event Listeners: In JavaScript, event listeners are a common source of memory leaks. Ensure that event listeners are properly removed when the associated elements are removed from the DOM.
4. Watch Out for Closures: While closures are useful in JavaScript, they can unintentionally retain memory if not used carefully. Be mindful of what variables are being closed over and ensure unnecessary references are cleaned up.
5. Monitor Memory Usage Regularly: Even if your application appears to be running smoothly, regularly monitor memory usage and set up alerts to detect memory spikes early. Tools like New Relic or Sentry can be valuable here.
6. Load tests: Run a load test simulating many requests against your production built prior to deploying it to production. This will prevent your users from being affected by memory leaks.

Conclusion

Memory leaks, if left undetected, can lead to significant performance issues in any application, whether on the frontend or server-side. At adagger, we’ve tackled memory leaks across a range of projects, from frontend frameworks like Vue.js to large-scale backend systems. By using proper monitoring tools, thoroughly profiling your code, and following best practices for resource cleanup, you can ensure your applications remain efficient and performant.

If you’re dealing with memory leaks or facing other performance challenges, we’d be happy to help. Feel free to reach out to our team of experts for a consultation and let’s make your application run as smoothly as possible!

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By sharing this real-world example of how we fixed a memory leak during a Vue.js migration, we hope to provide insight into common pitfalls and best practices, while demonstrating the value of a thorough approach to debugging.