next.js

7b01c98a - [turbopack-trace-server] Performance improvements for span event handling (#93179)

[turbopack-trace-server] Performance improvements for span event handling (#93179) ## What? Performance improvements for the turbopack-trace-server, optimizing how span events are stored, sorted, and retrieved. ## Why? When processing large traces, the trace server was spending significant time on: 1. Repeated sorting of events for each render in ExecutionOrder mode 2. Recomputing corrected self time on repeated lookups 3. Memory pressure from very large traces ## How? ### Lazy Sorting with LazySortedVec Introduces a new `LazySortedVec<T>` data structure that stores events unsorted and defers sorting until first read via `Deref`. Uses `UnsafeCell` + `Once` for thread-safe one-time sorting. This avoids repeated sorting overhead during trace ingestion. ### Pre-sorted Span Events by Start Time - `SpanEvent::Child` now stores its `start: Timestamp` alongside the index - `SpanEvent` implements `Ord` to sort by start time (with SelfTime before Child for equal timestamps) - The viewer's `ExecutionOrder` mode no longer needs to sort - events are already in order ### Cached Corrected Self Time - `SpanEvent::SelfTime` now wraps a `SpanEventSelfTime` struct containing an `OnceLock<Timestamp>` for `corrected_self_time` - The expensive tree lookup is performed once and cached for subsequent accesses - `SpanEventSelfTimeRef` provides access to the cached value via `corrected_self_time()` ### DROP_SPANS Environment Variable Adds `DROP_SPANS=<count>` env var to skip the first N spans when loading traces: - Useful for reducing memory usage with very large traces - Tracks dropped span IDs to also skip their subsequent events (End, SelfTime, etc.) - Stats output shows dropped span progress (e.g., "1000 spans, 500/1000 dropped") <!-- NEXT_JS_LLM_PR --> --------- Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>