feat: expose Lance metrics via OpenTelemetry in Python and Node (#3609)

Bridges Lance's internal `metrics`-crate instrumentation (object store
request counts, bytes, latency, errors, and throttles) into
OpenTelemetry, in both the Python and Node bindings, with a shared
adapter in the Rust core. This is the LanceDB counterpart to
lance-format/lance#7537.

## Rust core (`rust/lancedb`)
Two new, **off-by-default** features:
- `metrics` — re-exports the [`metrics`](https://docs.rs/metrics) crate
as `lancedb::metrics` and turns on Lance's object-store instrumentation.
Install any `metrics`-compatible recorder to collect them.
- `metrics-otel` — adds `lancedb::metrics_otel`, a pull-based adapter
that installs a process-global recorder aggregating into lock-free
cumulative storage and exposes a snapshot/catalog API
(`register_metrics_recorder`, `metrics_catalog`, `snapshot_metrics`,
`MetricPoint`/`MetricValue`/`MetricKind`/`MetricDescription`). Both
bindings build on this.

## Python
`lancedb.otel.instrument_lancedb_metrics()` registers each metric as an
OpenTelemetry observable instrument on the given (or global)
`MeterProvider`. Available via the `otel` extra (`pip install
lancedb[otel]`), which pulls in only `opentelemetry-api` — the
application supplies and configures the SDK.

## Node
`instrumentLanceDbMetrics()` provides the equivalent wiring against
`@opentelemetry/api`. This is the only public entry point; the
underlying recorder/catalog/snapshot functions stay internal.

Because OpenTelemetry has no asynchronous histogram instrument,
histograms are exported Prometheus-style as `<name>_bucket` (with an
`le` attribute), `<name>_count`, and `<name>_sum`. Only `_sum` carries
the histogram's unit; `_bucket` and `_count` observe cumulative counts
and are unitless. The adapter is enabled by default in the Python and
Node builds, and off by default in the Rust crate.

## Notes
- Requires Lance ≥ `v9.0.0-beta.19`, which ships the object-store
metrics APIs (upstream lance-format/lance#7537, now merged). `main` is
already on beta.19, so this is a single feature commit with no
dependency bump.
- Tests: 8 Rust unit tests, 3 Python tests, 2 Node tests, all covering
the end-to-end object-store-metrics → OpenTelemetry path.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nodejs/Cargo.toml

@@ -44,6 +44,6 @@ aws-lc-rs = "=1.16.3"
 napi-build = "2.3.1"
 
 [features]
-default = ["remote", "lancedb/aws", "lancedb/gcs", "lancedb/azure", "lancedb/dynamodb", "lancedb/oss", "lancedb/huggingface", "lancedb/goosefs"]
+default = ["remote", "lancedb/aws", "lancedb/gcs", "lancedb/azure", "lancedb/dynamodb", "lancedb/oss", "lancedb/huggingface", "lancedb/goosefs", "lancedb/metrics-otel"]
 fp16kernels = ["lancedb/fp16kernels"]
 remote = ["lancedb/remote"]

nodejs/__test__/otel.test.ts

@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+import {
+  MeterProvider,
+  type MetricData,
+  MetricReader,
+} from "@opentelemetry/sdk-metrics";
+import * as tmp from "tmp";
+import { connect, instrumentLanceDbMetrics } from "../lancedb";
+// snapshotLancedbMetrics is internal plumbing (not part of the public API), so
+// it is imported from the native module rather than the package entry point.
+import { snapshotLancedbMetrics } from "../lancedb/native";
+
+// The metrics recorder is process-global and installed once, so the whole
+// bridge is exercised in a single test to avoid cross-test global-state coupling.
+
+// A minimal pull-based reader whose `collect()` we drive directly, invoking the
+// observable-instrument callbacks. `@opentelemetry/sdk-metrics` ships no
+// in-memory reader, so we subclass the abstract base.
+class TestMetricReader extends MetricReader {
+  protected async onForceFlush(): Promise<void> {
+    // no-op: collection is driven directly via collect()
+  }
+  protected async onShutdown(): Promise<void> {
+    // no-op: nothing to release
+  }
+}
+
+async function metricsByName(
+  reader: TestMetricReader,
+): Promise<Map<string, MetricData>> {
+  const collected = await reader.collect();
+  const result = new Map<string, MetricData>();
+  for (const scope of collected.resourceMetrics.scopeMetrics) {
+    for (const metric of scope.metrics) {
+      result.set(metric.descriptor.name, metric);
+    }
+  }
+  return result;
+}
+
+describe("OpenTelemetry metrics bridge", () => {
+  let tmpDir: tmp.DirResult;
+  beforeEach(() => {
+    tmpDir = tmp.dirSync({ unsafeCleanup: true });
+  });
+  afterEach(() => tmpDir.removeCallback());
+
+  it("snapshot is safe to call regardless of install state", () => {
+    expect(Array.isArray(snapshotLancedbMetrics())).toBe(true);
+  });
+
+  it("exports object store metrics via observable instruments", async () => {
+    const reader = new TestMetricReader();
+    const provider = new MeterProvider({ readers: [reader] });
+    expect(instrumentLanceDbMetrics(provider)).toBe(true);
+
+    // Generate object store activity on the local filesystem (scheme "file").
+    const db = await connect(tmpDir.name);
+    const data = Array.from({ length: 256 }, (_, i) => ({ id: i }));
+    const table = await db.createTable("t", data);
+    expect(await table.countRows()).toBe(256);
+
+    const metrics = await metricsByName(reader);
+
+    const requests = metrics.get("lance_object_store_requests_total");
+    expect(requests).toBeDefined();
+    // biome-ignore lint/suspicious/noExplicitAny: SDK point shape
+    const requestPoints = (requests!.dataPoints as any[]) ?? [];
+    expect(requestPoints.length).toBeGreaterThan(0);
+    for (const p of requestPoints) {
+      // Labelled by `operation` and `base` (the store scheme by default).
+      expect(p.attributes).toHaveProperty("base");
+      expect(p.attributes).toHaveProperty("operation");
+    }
+    const totalRequests = requestPoints.reduce((acc, p) => acc + p.value, 0);
+    expect(totalRequests).toBeGreaterThan(0);
+
+    // Histograms are decomposed into bucket / count / sum observable counters.
+    const bucket = metrics.get(
+      "lance_object_store_request_duration_seconds_bucket",
+    );
+    expect(bucket).toBeDefined();
+    // biome-ignore lint/suspicious/noExplicitAny: SDK point shape
+    const bucketPoints = (bucket!.dataPoints as any[]) ?? [];
+    expect(bucketPoints.length).toBeGreaterThan(0);
+    expect(bucketPoints.every((p) => "le" in p.attributes)).toBe(true);
+    // The implicit +Inf bucket must be present.
+    expect(bucketPoints.some((p) => p.attributes.le === "+Inf")).toBe(true);
+
+    const count = metrics.get(
+      "lance_object_store_request_duration_seconds_count",
+    );
+    expect(count).toBeDefined();
+    // biome-ignore lint/suspicious/noExplicitAny: SDK point shape
+    const countPoints = (count!.dataPoints as any[]) ?? [];
+    expect(countPoints.reduce((acc, p) => acc + p.value, 0)).toBeGreaterThan(0);
+
+    const sum = metrics.get("lance_object_store_request_duration_seconds_sum");
+    expect(sum).toBeDefined();
+    // biome-ignore lint/suspicious/noExplicitAny: SDK point shape
+    const sumPoints = (sum!.dataPoints as any[]) ?? [];
+    expect(sumPoints.reduce((acc, p) => acc + p.value, 0)).toBeGreaterThan(0);
+
+    // Unit handling: only `_sum` keeps the histogram's unit (seconds); `_bucket`
+    // and `_count` observe cumulative counts and are unitless.
+    expect(sum!.descriptor.unit).toBe("s");
+    expect(bucket!.descriptor.unit).toBe("");
+    expect(count!.descriptor.unit).toBe("");
+
+    await provider.shutdown();
+  });
+});

nodejs/lancedb/index.ts

@@ -20,6 +20,11 @@ import { HeaderProvider } from "./header";
 // Re-export native header provider for use with connectWithHeaderProvider
 export { JsHeaderProvider as NativeJsHeaderProvider } from "./native.js";
 
+// OpenTelemetry metrics bridge. Only the high-level entry point is public; the
+// underlying recorder/catalog/snapshot functions remain internal plumbing that
+// `otel.ts` consumes from the native module.
+export { instrumentLanceDbMetrics } from "./otel";
+
 export {
   AddColumnsSql,
   ConnectionOptions,

nodejs/lancedb/otel.ts

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+import {
+  type Attributes,
+  type MeterProvider,
+  type ObservableResult,
+  metrics,
+} from "@opentelemetry/api";
+
+import {
+  lancedbMetricsCatalog,
+  registerLancedbMetricsRecorder,
+  snapshotLancedbMetrics,
+} from "./native";
+
+let instrumented = false;
+
+/**
+ * Register LanceDB metrics as OpenTelemetry observable instruments.
+ *
+ * Installs a process-global metrics recorder and creates one observable
+ * instrument per LanceDB metric (currently object store request counts, bytes,
+ * latency, errors, and throttles) on the given (or global) `MeterProvider`. The
+ * configured `MetricReader` then collects them on its own schedule.
+ *
+ * Counters and gauges map directly to observable counters/gauges. Because
+ * OpenTelemetry has no asynchronous histogram instrument, each histogram is
+ * exported Prometheus-style as cumulative `le` bucket counts (`<name>_bucket`,
+ * with an `le` attribute) plus `<name>_count` and `<name>_sum`.
+ *
+ * Requires `@opentelemetry/api` (a dependency) and, to actually export, an
+ * OpenTelemetry SDK such as `@opentelemetry/sdk-metrics`.
+ *
+ * @param meterProvider The provider to register instruments on. Defaults to the
+ *   global provider from `@opentelemetry/api`.
+ * @returns `true` if the recorder is installed and instruments are registered.
+ *   `false` if a different `metrics` recorder is already installed in this
+ *   process (only one global recorder is permitted), in which case a warning is
+ *   emitted and no instruments are created. Calling this more than once is safe;
+ *   instruments are created only on the first successful call.
+ */
+export function instrumentLanceDbMetrics(
+  meterProvider?: MeterProvider,
+): boolean {
+  if (!registerLancedbMetricsRecorder()) {
+    console.warn(
+      "Could not install the LanceDB metrics recorder: another `metrics` " +
+        "recorder is already installed in this process. LanceDB metrics will " +
+        "not be exported via OpenTelemetry.",
+    );
+    return false;
+  }
+
+  if (instrumented) {
+    return true;
+  }
+
+  const provider = meterProvider ?? metrics.getMeterProvider();
+  const meter = provider.getMeter("lancedb");
+
+  const scalarCallback = (metricName: string) => (result: ObservableResult) => {
+    for (const point of snapshotLancedbMetrics()) {
+      if (point.name === metricName && point.value != null) {
+        result.observe(point.value, point.attributes);
+      }
+    }
+  };
+
+  const bucketCallback = (metricName: string) => (result: ObservableResult) => {
+    for (const point of snapshotLancedbMetrics()) {
+      if (point.name !== metricName || point.buckets == null) {
+        continue;
+      }
+      for (const bucket of point.buckets) {
+        const attributes: Attributes = {
+          ...point.attributes,
+          le: bucket.le,
+        };
+        result.observe(bucket.cumulativeCount, attributes);
+      }
+    }
+  };
+
+  const fieldCallback =
+    (metricName: string, field: "count" | "sum") =>
+    (result: ObservableResult) => {
+      for (const point of snapshotLancedbMetrics()) {
+        if (point.name !== metricName) {
+          continue;
+        }
+        const value = point[field];
+        if (value != null) {
+          result.observe(value, point.attributes);
+        }
+      }
+    };
+
+  for (const desc of lancedbMetricsCatalog()) {
+    const unit = desc.unit ?? "";
+    if (desc.kind === "counter") {
+      const counter = meter.createObservableCounter(desc.name, {
+        unit,
+        description: desc.description,
+      });
+      counter.addCallback(scalarCallback(desc.name));
+    } else if (desc.kind === "gauge") {
+      const gauge = meter.createObservableGauge(desc.name, {
+        unit,
+        description: desc.description,
+      });
+      gauge.addCallback(scalarCallback(desc.name));
+    } else if (desc.kind === "histogram") {
+      // `_bucket` and `_count` observe cumulative sample counts, not the
+      // histogram's measured quantity, so they are unitless; only `_sum`
+      // carries the histogram's unit.
+      const bucket = meter.createObservableCounter(`${desc.name}_bucket`, {
+        description: `${desc.description} (cumulative buckets)`,
+      });
+      bucket.addCallback(bucketCallback(desc.name));
+
+      const count = meter.createObservableCounter(`${desc.name}_count`, {
+        description: `${desc.description} (count)`,
+      });
+      count.addCallback(fieldCallback(desc.name, "count"));
+
+      const sum = meter.createObservableCounter(`${desc.name}_sum`, {
+        unit,
+        description: `${desc.description} (sum)`,
+      });
+      sum.addCallback(fieldCallback(desc.name, "sum"));
+    }
+  }
+
+  instrumented = true;
+  return true;
+}

nodejs/package.json

@@ -44,6 +44,7 @@
     "@biomejs/biome": "^1.7.3",
     "@jest/globals": "^29.7.0",
     "@napi-rs/cli": "3.7.0",
+    "@opentelemetry/sdk-metrics": "^1.30.0",
     "@types/axios": "^0.14.0",
     "@types/jest": "^29.1.2",
     "@types/node": "22.7.4",
@@ -92,6 +93,7 @@
     "version": "napi version"
   },
   "dependencies": {
+    "@opentelemetry/api": "^1.9.0",
     "reflect-metadata": "^0.2.2"
   },
   "optionalDependencies": {

nodejs/pnpm-lock.yaml

@@ -8,6 +8,9 @@ importers:
 
   .:
     dependencies:
+      '@opentelemetry/api':
+        specifier: ^1.9.0
+        version: 1.9.1
       apache-arrow:
         specifier: '>=15.0.0 <=18.1.0'
         version: 18.1.0
@@ -33,6 +36,9 @@ importers:
       '@napi-rs/cli':
         specifier: 3.7.0
         version: 3.7.0(@emnapi/core@1.10.0)(@emnapi/runtime@1.10.0)(@types/node@22.7.4)
+      '@opentelemetry/sdk-metrics':
+        specifier: ^1.30.0
+        version: 1.30.1(@opentelemetry/api@1.9.1)
       '@types/axios':
         specifier: ^0.14.0
         version: 0.14.4
@@ -1307,6 +1313,32 @@ packages:
   '@octokit/types@16.0.0':
     resolution: {integrity: sha512-sKq+9r1Mm4efXW1FCk7hFSeJo4QKreL/tTbR0rz/qx/r1Oa2VV83LTA/H/MuCOX7uCIJmQVRKBcbmWoySjAnSg==}
 
+  '@opentelemetry/api@1.9.1':
+    resolution: {integrity: sha512-gLyJlPHPZYdAk1JENA9LeHejZe1Ti77/pTeFm/nMXmQH/HFZlcS/O2XJB+L8fkbrNSqhdtlvjBVjxwUYanNH5Q==}
+    engines: {node: '>=8.0.0'}
+
+  '@opentelemetry/core@1.30.1':
+    resolution: {integrity: sha512-OOCM2C/QIURhJMuKaekP3TRBxBKxG/TWWA0TL2J6nXUtDnuCtccy49LUJF8xPFXMX+0LMcxFpCo8M9cGY1W6rQ==}
+    engines: {node: '>=14'}
+    peerDependencies:
+      '@opentelemetry/api': '>=1.0.0 <1.10.0'
+
+  '@opentelemetry/resources@1.30.1':
+    resolution: {integrity: sha512-5UxZqiAgLYGFjS4s9qm5mBVo433u+dSPUFWVWXmLAD4wB65oMCoXaJP1KJa9DIYYMeHu3z4BZcStG3LC593cWA==}
+    engines: {node: '>=14'}
+    peerDependencies:
+      '@opentelemetry/api': '>=1.0.0 <1.10.0'
+
+  '@opentelemetry/sdk-metrics@1.30.1':
+    resolution: {integrity: sha512-q9zcZ0Okl8jRgmy7eNW3Ku1XSgg3sDLa5evHZpCwjspw7E8Is4K/haRPDJrBcX3YSn/Y7gUvFnByNYEKQNbNog==}
+    engines: {node: '>=14'}
+    peerDependencies:
+      '@opentelemetry/api': '>=1.3.0 <1.10.0'
+
+  '@opentelemetry/semantic-conventions@1.28.0':
+    resolution: {integrity: sha512-lp4qAiMTD4sNWW4DbKLBkfiMZ4jbAboJIGOQr5DvciMRI494OapieI9qiODpOt0XBr1LjIDy1xAGAnVs5supTA==}
+    engines: {node: '>=14'}
+
   '@protobufjs/aspromise@1.1.2':
     resolution: {integrity: sha512-j+gKExEuLmKwvz3OgROXtrJ2UG2x8Ch2YZUxahh+s1F2HZ+wAceUNLkvy6zKCPVRkU++ZWQrdxsUeQXmcg4uoQ==}
 
@@ -4925,6 +4957,27 @@ snapshots:
     dependencies:
       '@octokit/openapi-types': 27.0.0
 
+  '@opentelemetry/api@1.9.1': {}
+
+  '@opentelemetry/core@1.30.1(@opentelemetry/api@1.9.1)':
+    dependencies:
+      '@opentelemetry/api': 1.9.1
+      '@opentelemetry/semantic-conventions': 1.28.0
+
+  '@opentelemetry/resources@1.30.1(@opentelemetry/api@1.9.1)':
+    dependencies:
+      '@opentelemetry/api': 1.9.1
+      '@opentelemetry/core': 1.30.1(@opentelemetry/api@1.9.1)
+      '@opentelemetry/semantic-conventions': 1.28.0
+
+  '@opentelemetry/sdk-metrics@1.30.1(@opentelemetry/api@1.9.1)':
+    dependencies:
+      '@opentelemetry/api': 1.9.1
+      '@opentelemetry/core': 1.30.1(@opentelemetry/api@1.9.1)
+      '@opentelemetry/resources': 1.30.1(@opentelemetry/api@1.9.1)
+
+  '@opentelemetry/semantic-conventions@1.28.0': {}
+
   '@protobufjs/aspromise@1.1.2':
     optional: true
 

nodejs/src/lib.rs

@@ -12,6 +12,7 @@ mod header;
 mod index;
 mod iterator;
 pub mod merge;
+pub mod otel;
 pub mod permutation;
 mod query;
 pub mod remote;

nodejs/src/otel.rs

@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright The LanceDB Authors
+
+//! Node.js bindings over [`lancedb::metrics_otel`].
+//!
+//! The aggregation, catalog, and histogram bucketing all live in the LanceDB
+//! core crate; this module only converts the core snapshot types into napi
+//! objects and exposes the three entry points to JavaScript, where
+//! `lancedb/otel.ts` bridges them into the user's OpenTelemetry `MeterProvider`.
+
+use std::collections::HashMap;
+
+use lancedb::metrics_otel::{MetricPoint as CoreMetricPoint, MetricValue};
+use napi_derive::napi;
+
+/// One cumulative histogram bucket: all samples with value `<= le`.
+#[napi(object)]
+pub struct MetricBucket {
+    /// The inclusive upper bound of the bucket, or `"+Inf"` for the final bucket.
+    pub le: String,
+    /// Cumulative number of samples less than or equal to `le`.
+    pub cumulative_count: f64,
+}
+
+/// One aggregated metric data point. For counters and gauges only `value` is
+/// set; for histograms `buckets` (cumulative `le` counts), `count`, and `sum`
+/// are set.
+#[napi(object)]
+pub struct MetricPoint {
+    pub name: String,
+    pub kind: String,
+    pub attributes: HashMap<String, String>,
+    pub value: Option<f64>,
+    pub buckets: Option<Vec<MetricBucket>>,
+    pub count: Option<f64>,
+    pub sum: Option<f64>,
+}
+
+impl From<CoreMetricPoint> for MetricPoint {
+    fn from(point: CoreMetricPoint) -> Self {
+        let kind = point.kind.as_str().to_string();
+        let (value, buckets, count, sum) = match point.value {
+            MetricValue::Scalar(v) => (Some(v), None, None, None),
+            MetricValue::Histogram {
+                buckets,
+                count,
+                sum,
+            } => (
+                None,
+                Some(
+                    buckets
+                        .into_iter()
+                        // Counts stay well within the f64-exact integer range
+                        // (2^53), so this cast is lossless in practice and keeps
+                        // the values plain JS numbers for OpenTelemetry.
+                        .map(|(le, cumulative_count)| MetricBucket {
+                            le,
+                            cumulative_count: cumulative_count as f64,
+                        })
+                        .collect(),
+                ),
+                Some(count as f64),
+                Some(sum),
+            ),
+        };
+        Self {
+            name: point.name,
+            kind,
+            attributes: point.attributes,
+            value,
+            buckets,
+            count,
+            sum,
+        }
+    }
+}
+
+/// A described metric, used by the JavaScript layer to create instruments up front.
+#[napi(object)]
+pub struct MetricDescription {
+    pub name: String,
+    pub kind: String,
+    pub unit: Option<String>,
+    pub description: String,
+}
+
+/// Install the LanceDB metrics recorder as the process-global `metrics` recorder.
+///
+/// Returns `true` if the recorder is installed (now or previously). Returns
+/// `false` if a *different* recorder is already installed — `metrics` allows
+/// only one global recorder per process, so LanceDB cannot coexist with another.
+#[napi]
+pub fn register_lancedb_metrics_recorder() -> bool {
+    lancedb::metrics_otel::register_metrics_recorder()
+}
+
+/// The catalog of described LanceDB metrics. Empty until the recorder is installed.
+#[napi]
+pub fn lancedb_metrics_catalog() -> Vec<MetricDescription> {
+    lancedb::metrics_otel::metrics_catalog()
+        .into_iter()
+        .map(|desc| MetricDescription {
+            name: desc.name,
+            kind: desc.kind.as_str().to_string(),
+            unit: desc.unit,
+            description: desc.description,
+        })
+        .collect()
+}
+
+/// A point-in-time snapshot of every recorded metric. Empty until the recorder
+/// is installed.
+#[napi]
+pub fn snapshot_lancedb_metrics() -> Vec<MetricPoint> {
+    lancedb::metrics_otel::snapshot_metrics()
+        .into_iter()
+        .map(MetricPoint::from)
+        .collect()
+}