Not measuring App Start on consequent start

[rodolfoBee]

What React Native libraries do you use?

Expo (mobile only)

Are you using sentry.io or on-premise?

sentry.io (SaS)

@sentry/react-native SDK Version

6.1.0

How does your development environment look like?

NA

Sentry.init()

const nativeTracingIntegration = Sentry.reactNativeTracingIntegration({
idleTimeoutMs: 20000
});
const navigationIntegration = Sentry.reactNavigationIntegration({
enableTimeToInitialDisplay: true,
routeChangeTimeoutMs: 20000,
ignoreEmptyBackNavigationTransactions: false
});

Sentry.init({
dsn: CONFIG.SENTRY.DSN,
enableAutoSessionTracking: true,
environment: CONFIG.SENTRY.ENVIRONMENT,
normalizeDepth: 5,
tracesSampleRate: 1,
profilesSampleRate: 0,
integrations: [nativeTracingIntegration, navigationIntegration],
debug: DEV,
});

Steps to Reproduce

1. Build the app and run it on an Android device
2. Start the app and use any other tool to estimate the TTID of the app.
3. Close the app
4. Repeat step 2

I was not able to reproduce due to the lack of available test devices.

Expected Result

The measurement you make matches the TTID shown in the Sentry transactions reported by the application.

Actual Result

The TTID reported when the application is opened for the second time (step 4) does not match the measurements made.

In the tests, both load time take about 7 seconds. The first trace reported by sentry contains the cold start measurement and matches the user loading time experience:

The second app start also takes about 7 seconds, but the transaction and TTID display in Sentry do not reflect it:

The second transaction also do not report the app as "cold start".

[krystofwoldrich]

Thank you @rodolfoBee for the details.

To investigate this, we would need the JS logs from the second application start.

From what I can see in the screenshots the reason for the shorter TTID is the missing app start as you mentioned.

There are multiple reasons for the app start to be missing, the logs would help us to investigate it further.

sentry-react-native/packages/core/src/js/tracing/integrations/appStart.ts

Lines 219 to 255 in e0ccb78

	const appStart = await NATIVE.fetchNativeAppStart();
	if (!appStart) {
	logger.warn('[AppStart] Failed to retrieve the app start metrics from the native layer.');
	return;
	}
	if (appStart.has_fetched) {
	logger.warn('[AppStart] Measured app start metrics were already reported from the native layer.');
	return;
	}
	const appStartTimestampMs = appStart.app_start_timestamp_ms;
	if (!appStartTimestampMs) {
	logger.warn('[AppStart] App start timestamp could not be loaded from the native layer.');
	return;
	}
	const appStartEndTimestampMs = recordedAppStartEndTimestampMs || getBundleStartTimestampMs();
	if (!appStartEndTimestampMs) {
	logger.warn(
	'[AppStart] Javascript failed to record app start end. `setAppStartEndTimestampMs` was not called nor could the bundle start be found.',
	);
	return;
	}
	const isAppStartWithinBounds =
	!!event.start_timestamp && appStartTimestampMs >= event.start_timestamp - MAX_APP_START_AGE_MS;
	if (!__DEV__ && !isAppStartWithinBounds) {
	logger.warn('[AppStart] App start timestamp is too far in the past to be used for app start span.');
	return;
	}
	const appStartDurationMs = appStartEndTimestampMs - appStartTimestampMs;
	if (!__DEV__ && appStartDurationMs >= MAX_APP_START_DURATION_MS) {
	// Dev builds can have long app start waiting over minute for the first bundle to be produced
	logger.warn('[AppStart] App start duration is over a minute long, not adding app start span.');
	return;
	}