nextjs pageload transactions should exclude <Link/> prefetch #18175
Description
Is there an existing issue for this?
- I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
- I have reviewed the documentation https://docs.sentry.io/
- I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases
How do you use Sentry?
Sentry Saas (sentry.io)
Which SDK are you using?
@sentry/nextjs
SDK Version
10.25.0
Framework Version
Next 15.5.4 (app router, webpack bundler)
Link to Sentry event
event -- this particular trace is from SDK 10.14.0 but the issue exists on latest release, too.
Reproduction Example/SDK Setup
Basically normal configuration...
Sentry.init({
dsn: process.env.NEXT_PUBLIC_SENTRY_DSN,
environment: process.env.NEXT_PUBLIC_SENTRY_ENV,
release: process.env.NEXT_PUBLIC_SENTRY_RELEASE,
tracesSampleRate: Number(process.env.NEXT_PUBLIC_SENTRY_SAMPLE_RATE),
tracePropagationTargets: [
`^${process.env.NEXT_PUBLIC_BACKEND_URL}/api`, // regex to match backend for distributed tracing
`^${process.env.NEXT_PUBLIC_HAVEN_URL}`, // regex to match haven for distributed tracing
],
sendDefaultPii: false,
});Steps to Reproduce
You can make an app router page with a <Link> to another page in next 15, and your pageload transactions will start including child spans for ?_rsc prefetches. Note that next doesn't do the prefetch when running the dev server, so you have to run a production build to cause those child spans.
Expected Result
I'd expect prefetch to be excluded from pageload timings because the prefetch happens after the page is rendered and interactive.
Actual Result
The prefetches extend pageload timings, sometimes by multiple seconds (our users often have low bandwidth).
Additional Context
Pageload appears to based on idleTimeout. Child spans are being created well after pageload that keep the pageload transaction open. This leads to significantly broken reporting of nextjs pageload timings.
Excluding ?_rsc spans
I can exclude these spans by configuring the browserTracingIntegration:
browserTracingIntegration({
shouldCreateSpanForRequest: (url: string) => {
// Exclude RSC preloads
// Note: this also excludes these spans from navigation transactions, but that's an acceptable trade...
if (url.includes("?_rsc=") || url.includes("&_rsc=")) {
return false;
}
// Create spans for all other requests
return true;
},
}),...but that has the unfortunate side effect (as noted in the comment) of also excluding them for navigation transactions, for which they are one of the most important spans!
Filtering spans higher in the config
The top-level sentry config provides another hook called beforeSendTransaction that exposes various spans (where we could filter out rsc), but I'm not confident modifying that span array wouldn't break something else. E.g. just poking around I found another property that reference the span count.
Mostly, though, I'd expect the sdk to exclude these prefetch spans without additional configuration, as for most sites their inclusion will distort timing.