perf(otlp): eliminate unnecessary SpanData clones in tonic and HTTP exporters

The tonic trace exporter deep-cloned every SpanData into a Vec on each
export call, even though SpanBatch already provides borrowed access to
the underlying slice. Replace Arc<Vec<SpanData>> with Arc<SpanBatch> to
wrap the borrowed data directly (~free), matching the existing pattern
used by the tonic logs exporter with Arc<LogBatch>.

The HTTP trace exporter had the same unnecessary clone in
build_trace_export_body — removed by using SpanBatch::as_slice()
directly.

Adds SpanBatch::as_slice() for callers needing &[SpanData].

Author: bryantbiggs

opentelemetry-otlp/CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## vNext
 
-- Updated trace exporters to use borrowed `SpanBatch` interface, reducing allocations in the export path.
+- Updated trace exporters to use borrowed `SpanBatch` interface, eliminating unnecessary `SpanData` deep clones in tonic and HTTP trace exporters.
 - Add `build()` directly on `SpanExporterBuilder`, `MetricExporterBuilder`, and `LogExporterBuilder`
   (before selecting a transport), which auto-selects the transport based on the
   `OTEL_EXPORTER_OTLP_PROTOCOL` environment variable or enabled features.

opentelemetry-otlp/src/exporter/http/mod.rs

@@ -587,8 +587,7 @@ impl OtlpHttpClient {
         spans: SpanBatch<'_>,
     ) -> Result<(Vec<u8>, &'static str, Option<&'static str>), String> {
         use opentelemetry_proto::tonic::collector::trace::v1::ExportTraceServiceRequest;
-        let span_data: Vec<_> = spans.iter().cloned().collect();
-        let resource_spans = group_spans_by_resource_and_scope(&span_data, &self.resource);
+        let resource_spans = group_spans_by_resource_and_scope(spans.as_slice(), &self.resource);
 
         let req = ExportTraceServiceRequest { resource_spans };
         let (body, content_type) = match self.protocol {

opentelemetry-otlp/src/exporter/tonic/trace.rs

@@ -72,7 +72,7 @@ impl TonicTracesClient {
 
 impl SpanExporter for TonicTracesClient {
     async fn export(&self, batch: SpanBatch<'_>) -> OTelSdkResult {
-        let batch: Arc<Vec<_>> = Arc::new(batch.iter().cloned().collect());
+        let batch = Arc::new(batch);
 
         match super::tonic_retry_with_backoff(
             #[cfg(feature = "experimental-grpc-retry")]
@@ -108,7 +108,7 @@ impl SpanExporter for TonicTracesClient {
                     })?;
 
                 let resource_spans =
-                    group_spans_by_resource_and_scope(&batch_clone, &self.resource);
+                    group_spans_by_resource_and_scope(batch_clone.as_slice(), &self.resource);
 
                 otel_debug!(name: "TonicTracesClient.ExportStarted");
 

opentelemetry-sdk/CHANGELOG.md

@@ -5,7 +5,7 @@
 - **Breaking** The SDK `testing` feature is now runtime agnostic. [#3407][3407]
   - `TokioSpanExporter` and `new_tokio_test_exporter` have been renamed to `TestSpanExporter` and `new_test_exporter`.
   - The following transitive dependencies and features have been removed: `tokio/rt`, `tokio/time`, `tokio/macros`, `tokio/rt-multi-thread`, `tokio-stream`, `experimental_async_runtime`
-- **Breaking** `SpanExporter::export` now takes `SpanBatch<'_>` instead of `Vec<SpanData>`, matching the borrowed `LogBatch` pattern used in the logs pipeline. This eliminates per-export `Vec` allocations in `BatchSpanProcessor`. Implementors should update their `export` signatures and use `batch.iter()` to access spans.
+- **Breaking** `SpanExporter::export` now takes `SpanBatch<'_>` instead of `Vec<SpanData>`, matching the borrowed `LogBatch` pattern used in the logs pipeline. This eliminates per-export `Vec` allocations in `BatchSpanProcessor`. Implementors should update their `export` signatures and use `batch.iter()` or `batch.as_slice()` to access spans.
 - Add 32-bit platform support by using `portable-atomic` for `AtomicI64` and `AtomicU64` in the metrics module. This enables compilation on 32-bit ARM targets (e.g., `armv5te-unknown-linux-gnueabi`, `armv7-unknown-linux-gnueabihf`).
 - `Aggregation` enum and `StreamBuilder::with_aggregation()` are now stable and no longer require the `spec_unstable_metrics_views` feature flag.
 - Fix `service.name` Resource attribute fallback to follow OpenTelemetry

opentelemetry-sdk/src/trace/export.rs

@@ -30,6 +30,11 @@ impl<'a> SpanBatch<'a> {
     pub fn iter(&self) -> impl Iterator<Item = &SpanData> {
         self.data.iter()
     }
+
+    /// Returns the underlying slice of span data.
+    pub fn as_slice(&self) -> &'a [SpanData] {
+        self.data
+    }
 }
 
 /// `SpanExporter` defines the interface that protocol-specific exporters must