fix(trace-stats)!: add grpc_method to aggregation key#2151
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Spans with different gRPC methods were previously merged into the same stats group (only the first span's method was kept). Adding grpc_method to FixedAggregationKey ensures each method gets a separate bucket. The OtlpExactGroup.grpc_method field is now sourced from the key rather than a GroupedStats sidecar. The agent /v0.6/stats protobuf wire format is unchanged (no grpc_method field in ClientGroupedStats). SHM_VERSION bumped to 2 because FixedAggregationKey<StringRef> is #[repr(C)] and the new field changes the layout; mismatched sidecar/worker pairs will safely fail with a version-mismatch error. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Bincode encodes struct fields positionally. Inserting grpc_method before http_status_code shifted all subsequent field positions, breaking IPC fallback decoding (OwnedShmSpanInput) between mismatched worker/sidecar versions. Moving it to the end of the struct preserves all existing field positions, so old-format IPC messages are decoded correctly up to the grpc_method field; the decode then fails with EOF rather than silently misinterpreting existing fields. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Some concerns regarding cardinality for non-otlp exporter otherwise LGTM
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…xport span.resource already carries the full gRPC method path for gRPC spans (e.g. /package.Service/Method). Adding grpc_method as a separate aggregation dimension or OTLP attribute is redundant and adds cardinality. Removes: - grpc_method from FixedAggregationKey - grpc_method from OtlpExactGroup - rpc.method from the OTLP data-point attributes emitted by build_attributes - GRPC_METHOD_FIELD constant and get_grpc_method() helper Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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What does this PR do?
Removes `grpc_method` / `rpc.method` entirely from the OTLP trace metrics pipeline.
Previously `grpc_method` was a sidecar on `GroupedStats` — present in the OTLP metric payload as an explicit attribute, but not part of the aggregation key. This PR removes it from both:
Rationale
For gRPC spans, `span.resource` already carries the full method path (e.g. `/package.Service/Method`). Emitting `rpc.method` as a separate OTLP attribute is redundant — `span.resource` (mapped to `span.name` on the data point) is the authoritative carrier of gRPC method identity and is already an aggregation dimension.
Adding `rpc.method` as a separate dimension would also increase cardinality for gRPC services without providing any information not already present on the metric.
Note: `rpc.response.status_code` (from `grpc.status.code`) is kept as a first-class aggregation dimension — it is not redundant with any existing field.
Motivation
Correctness and cleanliness for the OTLP trace metrics feature landed in #2067.
Risk
Breaking changes (major semver):
Blast radius is limited because:
Urgency: low. No live production systems are affected. This must land before the next release that ships the OTLP metrics feature.
How to test the change?