What is "Collecting build traces" doing?

[selalipop]

Summary

It's adding 10 minutes to my CI build, and I assumed it was the tracing required for 'standalone' builds.

But now even with next build + next start it's running and taking more time than the actual build.

Is this behavior expected? This isn't an extremely large project either.

Additional information

No response

Example

No response

[icyJoseph]

This is documented in long form here, https://nextjs.org/docs/app/api-reference/config/next-config-js/output

During a build, Next.js will automatically trace each page and its dependencies to determine all of the files that are needed for deploying a production version of your application.

This feature helps reduce the size of deployments drastically. Previously, when deploying with Docker you would need to have all files from your package's dependencies installed to run next start. Starting with Next.js 12, you can leverage Output File Tracing in the .next/ directory to only include the necessary files.

One of the special things with standalone builds, is that:

Next.js can automatically create a standalone folder that copies only the necessary files for a production deployment including select files in node_modules.

[samson501]

Having the same issue. I'm trying to speed up my Next.js CI test build, which just needs to test for a successful build, and doesn't need build traces.

[m0sa]

Same here, please add an opt out!

[icyJoseph]

Has anyone tried out Turbopack for builds? It uses Turbotracer (I think that's the name), and should be way faster.

[samson501]

Has anyone tried out Turbopack for builds? It uses Turbotracer (I think that's the name), and should be way faster.

Using the --turbopack flag does improve the speed of the Compiling step, however the issue here is moreso that there are other unecessary steps taking significant time with no way to skip them. Turbopack is also unavailable to anyone on projects below Next 15.

[icyJoseph]

Are you guys using sentry btw?

[samson501]

I seem to have found a solution on Next.js 14, however it says that this will no longer be an option in the next major version (15). No idea what would compel them to remove this feature.

Setting outputFileTracing to false in the Next config still results in them displaying in the output log, however they will finish immediatley.

/** @type {import('next').NextConfig} */
const nextConfig = {
  ...
  outputFileTracing: false,
  ...
}

Implementing this has cut my CI's next build times in half. I can only hope that they introduce something similar in Next.js 16.

[icyJoseph]

I guess you can still exclude them with a glob pattern like, for CI only.