When investigating slow app starts or TTFD, users currently need to dig into individual HTTP request spans to determine if network activity was the cause. Adding aggregate network measurements to the parent span would answer "was this slow startup caused by network?" at a glance.
Proposed measurements on app start and TTFD spans:
- Request count
- Failed request count
- Total duration
- Slowest request duration + host
Feasibility Assessment (Jul 2026)
Not yet covered — individual HTTP child spans exist under app start/TTFD transactions, but no aggregation onto the parent span.
Cross-SDK alignment: No other Sentry SDK (Cocoa, Android, Flutter) aggregates HTTP request data onto app start or TTFD spans. This would be RN-first with no cross-SDK precedent.
Spec: No develop.sentry.dev spec defines aggregate HTTP measurement keys. The span data conventions only cover individual HTTP span attributes. A new spec would need to be proposed.
Dashboard visibility: Custom measurements are queryable in Discover/custom widgets, but would not appear in the built-in Performance/App Starts pages (hardcoded to standard measurements). Also, Relay enforces a limit of ~10 custom measurements per event — adding 4-5 measurements would consume significant budget and could displace user-defined custom measurements.
Note: The modern direction (especially in JS SDK) is moving toward span attributes rather than transaction-level measurements, with span metrics infrastructure extracting data. Consider span attributes over measurements when designing.
Implementation approach
Collect HTTP request child spans during the app start / TTFD window and compute aggregates at span finalization time. Needs cross-integration coordination between HTTP instrumentation and app start/TTFD span lifecycle.
When investigating slow app starts or TTFD, users currently need to dig into individual HTTP request spans to determine if network activity was the cause. Adding aggregate network measurements to the parent span would answer "was this slow startup caused by network?" at a glance.
Proposed measurements on app start and TTFD spans:
Feasibility Assessment (Jul 2026)
Not yet covered — individual HTTP child spans exist under app start/TTFD transactions, but no aggregation onto the parent span.
Cross-SDK alignment: No other Sentry SDK (Cocoa, Android, Flutter) aggregates HTTP request data onto app start or TTFD spans. This would be RN-first with no cross-SDK precedent.
Spec: No develop.sentry.dev spec defines aggregate HTTP measurement keys. The span data conventions only cover individual HTTP span attributes. A new spec would need to be proposed.
Dashboard visibility: Custom measurements are queryable in Discover/custom widgets, but would not appear in the built-in Performance/App Starts pages (hardcoded to standard measurements). Also, Relay enforces a limit of ~10 custom measurements per event — adding 4-5 measurements would consume significant budget and could displace user-defined custom measurements.
Note: The modern direction (especially in JS SDK) is moving toward span attributes rather than transaction-level measurements, with span metrics infrastructure extracting data. Consider span attributes over measurements when designing.
Implementation approach
Collect HTTP request child spans during the app start / TTFD window and compute aggregates at span finalization time. Needs cross-integration coordination between HTTP instrumentation and app start/TTFD span lifecycle.