CODEWITHSUNDEEP
javascriptnode.jsprocess
Madhusudhan
Madhusudhan

Reputation: 8563

async operations in nodejs express

I am having a route

app.get('/posts', function (req, res) {
  res.json([
    // data
  ]);

  // what would happen to the code below
  // Suppose it is processing a million records
  processMillionRecords();
});

function processMillionRecords () {
  // process million records
}

Once the response is sent, another function is called which is quite an expensive operation. What would happen if this continues? Are there any implications?

I know the ideal way of doing it is using background processes. So I replaced it with the below.

res.json([
  // data
]);

var child = require('child_process');
child.fork('worker.js');

// worker.js
function processMillionRecords () {
  // process million records
}

Which one is more preferred and in which cases?

Upvotes: 2

Views: 204

Answers (2)

rdegges
rdegges

Reputation: 33864

What will happen in the situation described above (as mentioned by Timothy), is this:

  • Your app will return data to the user quickly.
  • Your Node process will continue to run the async code behind the scenes until the process has finished.

If you're building an app that is expecting a lot of traffic, or a lot of CPU intensive workload, it's best to move this stuff into a separate server specifically meant for processing long-running tasks. This reduces the chance that:

  • Your web server reboots -- destroying your background processing stuff.
  • Your web server is processing too many background tasks to properly handle incoming user requests.

Hope that helps.

Upvotes: 0

Timothy Strimple
Timothy Strimple

Reputation: 23070

Node is built to handle long asynchronous operations. Unless it's very CPU heavy, you probably don't need to fork a new worker process. Just write your processMillionRecords to be async and make sure it doesn't block the event loop.

Upvotes: 2

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