subms-otel

OpenTelemetry bridge for the subms perf harness. Plugs into the harness's SubMsObserver hook and the post-bench SubMsBenchSummary / SubMsTimer types to emit Histogram + Span data without the harness itself pulling in the OTEL dependency tree.

Pair with the cookbook primer at https://submillisecond.com/cookbook/primers/subms-otel for the walkthrough.

Install

[dependencies]
subms = "0.5"
subms-otel = { version = "0.5", features = ["sync"] }

Pick the feature that matches the cost you're willing to pay on the bench hot path:

Feature	Surface
`bridge`	`export_summary`, `export_timer`, `histogram_boundaries`, `CompositeObserver`
`sync`	`OtelObserver` - synchronous `Histogram::record` per sample
`async`	`OtelObserverAsync` - bounded channel + background drain thread
`otlp`	`OtlpBuilder` - opt-in OTLP exporter wiring
`prometheus`	`PrometheusBuilder` - opt-in Prometheus exporter wiring

Default features pull in just bridge.

Quickstart - wire `OtelObserver`

use std::sync::Arc;
use opentelemetry::metrics::MeterProvider;
use opentelemetry_sdk::metrics::SdkMeterProvider;
use subms::{SubMsPerfHarness, summarize};
use subms_otel::OtelObserver;

let provider = SdkMeterProvider::builder().build();
let meter = provider.meter("my-recipe");

let mut h = SubMsPerfHarness::new("my-workload", "rust")
    .with_observer(Arc::new(OtelObserver::new(meter)));

let put = h.stage("put", 1_000);
for _ in 0..1_000 { put.time(|| { /* work */ }); }

// on_summarize re-emits the full attribute set drawn from inputs + meta.
let _ = summarize(&h);

Semantic conventions

Every emission carries this attribute table (keys are stable, consumers filter on them in dashboards):

Attribute key	Source
`subms.workload`	`ctx.workload` / `summary.workload`
`subms.lang`	`ctx.lang` / `summary.lang`
`subms.stage`	`ctx.stage` / stage name
`subms.stage.kind`	`ctx.stage_kind.as_str()`
`subms.recipe.slug`	`meta["subms.recipe.slug"]`
`subms.recipe.category`	`meta["subms.recipe.category"]`
`subms.workload.feature`	`meta["subms.workload.feature"]`
`subms.workload.entries`	`inputs["entries"]`
`subms.workload.seed`	`inputs["seed"]`
`subms.host`	`meta["host"]`
`subms.hardware.tier`	`meta["hardware_tier"]`
`subms.crate.version`	`meta["crate_version"]`

Inputs and meta arrive only via on_summarize (the harness's ObservationCtx is intentionally minimal). The sync observer therefore records hot-path samples with just the first four attributes; the on_summarize hook re-emits the headline percentiles plus downsampled samples under the fuller set.

Status

Pre-1.0. The harness JSON contract is stable since subms 0.2; the observer surface is stable since subms 0.5.1. The OTLP / Prometheus helpers are thin starter wrappers - production deployments should wire their own MeterProvider for control over batching, resource attrs, and transport.

Licence

Dual licensed under MIT or Apache-2.0.