Module metrics 

Observability for the streaming engine.

The scheduler can optionally report, for every completed HTTP request, a RequestStats record and, when the stream ends, an aggregate StreamSummary. These are surfaced through the StreamObserver trait, which is attached explicitly via Client::stream_arrow_with_observer.

StreamMetrics is a ready-made, thread-safe observer implementation (atomics plus a small fixed histogram) that the caller constructs, passes in, and reads from during or after the stream. Power users can implement StreamObserver themselves to collect raw RequestStats (for exact percentiles, custom exporters, etc.).

When no observer is attached the engine does no metrics work at all — there is zero overhead on the default streaming paths.

Structs

RequestStats

Metrics for a single completed HTTP request, reported via StreamObserver::on_request.

StreamMetrics

Thread-safe aggregate metrics handle.

StreamSummary

Aggregate summary of a stream run, produced by StreamMetrics::summary and passed to StreamObserver::on_finish.

Enums

RequestKind

Whether a scheduled request extended the frontier or backfilled a gap left by an earlier truncated response.

Constants

NUM_SIZE_BUCKETS

Number of size-vs-target histogram buckets.

SIZE_BUCKET_LABELS

Human-readable labels for the size-vs-target histogram buckets, relative to response_bytes_target.

Traits

StreamObserver

Observer that receives streaming metrics.