With sampling rate 0, transactions are still recorded

[PankajSati-apl]

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/react

SDK Version

9.28.1

Framework Version

18.3.0

Link to Sentry event

No response

Reproduction Example/SDK Setup

Sentry.init({
   ...
    tracesSampler(_) {
      return getCurrentSamplingRate(); // Reads global variable, updated when user data is initialized. We want to only record the paid users
    },
   ...
})

Steps to Reproduce

1. Initialised Sentry with tracesSampler
2. Added samplingRate as custom attribute
3. Observed that transactions with sampling Rate 0 are reported in Sentry

Expected Result

Transactions with sampling Rate 0 should be dropped

Actual Result

Transactions with sampling Rate 0 are getting reported to Sentry

[Lms24]

Hey @PankajSati-apl thanks for writing in!

Can you provide a minimal reproduction for this bug report? The currently posted code is not enough for us to reproduce this.

Added samplingRate as custom attribute
Observed that transactions with sampling Rate 0 are reported in Sentry

While I'm not 100% sure, I guess you mean that you add a span attribute with the sample rate you attach onto the global variable? Are you reading this variable at exactly the same time as when the tracesSampler callback is called? I'm asking because based on your description, I could see tracesSampler initially returning a >0 rate and the global variable being updated only later to 0 when the root span was already started. Though again, without a reproduction, this is only a wild guess.

[PankajSati-apl]

@Lms24
Here is my current setup (Have omitted beforeSend from the snippet)

  Sentry.init({
    environment: process.env.SENTRY_ENV,
    enabled: true, 
    dsn: SENTRY_DSN,
    attachStacktrace: true,
    tracesSampler(_) {
       return getCurrentSamplingRate();
    },
    profilesSampleRate: 0.01,
    ignoreErrors: SentryIgnoreList,
  });

In my App component, I am setting the sampling rate based on user_id and their subscription status.

export function getCurrentSamplingRate(): number {
  return window.__SENTRY_TRACES_SAMPLER__ ?? 0;
}

//Calculated in AppComponent. Goal is to sample all transactions of the paid users i.e. samplingRate = 1.0 and others should be dropped (0 sampling rate)
function setSamplingRate(rate: number): void {
  window.__SENTRY_TRACES_SAMPLER__ = rate;
}

---

1. One observation is that I am using 0 sampling rate when app is loaded (before my AppComponent is even mounted). This should result in sampling rate 0 and all page load transactions should be dropped. However, I am still seeing pageload events in Sentry dashboard.

2. Using Traces dashboard, I added sampling_rate column (Query: has:sampling_rate). Can you tell what this represents? Is this the sampling rate for the current span/transaction? This value is not sent from the app.