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V8 Heap | Create a Dump of the V8 Heap and Inspect It for Your Node App

  idkblogs.com      October 12, 2019

Shubham Verma

Shubham Verma


V8 Heap | Create a Dump of the V8 Heap and Inspect It for Your Node App

V8

dump is basically for memory managemnt, this is an important part of web app development. In the v8 dump you can know about all the aspects of memory like number of object instances, Shallow Size, Retained Size and distance.
In this article, we will learn how we can take a dump of the V8 heap and inspect that heap, and we will also learn how to record heap snapshots with the Chrome DevTools heap profiler and find memory leaks.
Node.js is getting more popular and various types of apps are using Node.js as a back-end solution, thus we need to ensure that our application doesn’t have a memory leak.
To ensure that our app doesn’t have a memory leak, we will take heap dumps. A heap dump can contain data that can help in finding the memory leaks. So, to do this, we will integrate the npm module heap dump into our app.

let's have a look about the terms related to v8 dump:

Constructor:

Constructor represents all objects created using this constructor

Shallow size:

The shallow size column in v8 displays the sum of shallow sizes of all objects - created by a certain constructor function. The shallow size is the size of memory held by an object itself (generally, arrays and strings have larger shallow sizes)

Retained size:

Retained size column displays the maximum retained size among the same set of objects. The size of memory that can be freed once an object is deleted (and this its dependents made no longer reachable) is called the retained size.

Number of object instances:

Number of object instances is displayed in the # column.

Distance:

Distance displays the distance to the root using the shortest simple path of nodes.

Create a Dump of the V8 Heap and Inspect It for Your Node App

Create a Dump of the V8 Heap and Inspect It for Your Node App



For the demonstration, we will create a small Node application that has a file app.js and follows the steps below.

Step 1. Create a Node App:

In this step, we'll create a folder, named "heapdump-demo", and add a file "app.js" into it.

app.js:


                                const heapdump = require('heapdump');
                                const express = require('express');
                                const app = express();
                    
                                app.get('/', (req, res) => {
                                   res.send(`

You are at the best place to learn

`); }) heapdump.writeSnapshot('/' + Date.now() + '.heapsnapshot'); heapdump.writeSnapshot(function (err, filename) { console.log('dump written to', filename); }); app.listen(8080, () => { console.log(`go to http://localhost:8080/`) });

Step 2. Install Dependencies:

Now, its time to install the related dependencies, So open your terminal and go to the file location. Install the dependencies by using the command below:

npm install express heapdumpo
Create a Dump of the V8 Heap and Inspect It for Your Node App

Snapshot of ‘npm install express heapdump’

Step 3. Run the App

Run the app using the below command:

env NODE_HEAPDUMP_OPTIONS=nosignal node app.js
Create a Dump of the V8 Heap and Inspect It for Your Node App

output of command "env NODE_HEAPDUMP_OPTIONS=nosignal node app.js"

Open the browser and hit the URL http://localhost:8080/. (Keep it open.)

Now, in the terminal, there is a message:

"dump written to heapdump-280936526.45328.heapsnapshot"
It means that your heap-snapshot is created. Now you need to use this dump.

You can also see this heap dump file in VS Code. (I am using VS Code.)

Create a Dump of the V8 Heap and Inspect It for Your Node App

Snapshot of file “heapdump-280936526.45328.heapsnapshot”

Now, open your file heapdump-280936526.45328.heapsnapshot in VS Code. It looks like the below image:

Create a Dump of the V8 Heap and Inspect It for Your Node App

file heapdump-280936526.45328.heapsnapshot

Step 4. Upload Heap Dump to Chrome DevTools:

To upload this heap dump, you need to follow the below instructions.
Open the Chrome browser => open Chrome DevTools => go to memory => click on Load button => load the file heapdump-280936526.45328.heapsnapshot from its specific location.

Create a Dump of the V8 Heap and Inspect It for Your Node App

Chrome DevTools

After successfully loading, you can see this file in the left-hand side of the Chrome tool under Profile and HEAP SNAPSHOTS, as below:

Create a Dump of the V8 Heap and Inspect It for Your Node App

Showing uploaded snapshots

Step 5: Inspect Data

Click on the uploaded file heapdump-280936526.45328.heapsnapshot and inspect the data.
You can see a summary here:

Create a Dump of the V8 Heap and Inspect It for Your Node App

Summary

You can see the containment:

Create a Dump of the V8 Heap and Inspect It for Your Node App

Containment

You can see the statistics:

Create a Dump of the V8 Heap and Inspect It for Your Node App

Statistics

Conclusion

In this article, we learned about the v8 dump and also learned how you can create your heap dump based on conditions using the below code and compare the data:


                        heapdump.writeSnapshot('/' + Date.now() + '.heapsnapshot');
                        
                        heapdump.writeSnapshot(function (err, filename) {
                            console.log('dump written to', filename);
                        });
                      

This code is responsible for creating a heap dump. Now you can add this into your project, create a heap dump, and inspect it.

Congratulations, you are becoming an expert in Node.js


If you want to learn more about memory leaks or Node app profiling, or want to know more about heap dumps and its memory, read the RELATED POSTS below:


Thank you

for taking the time to read this article. If you’re interested in Node.js or JavaScript this link will help you a lot.



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