Observability

Lance can publish operational metrics to your monitoring stack. The table below is the authoritative catalogue of the metrics Lance emits, shared verbatim with the Rust lance::metrics module documentation.

Lance publishes metrics through the metrics crate facade. Install any recorder (Prometheus, OpenTelemetry, etc.) in your application and Lance will emit into it; when no recorder is installed, emission is a cheap no-op. Metrics are only emitted when Lance is built with the metrics feature.

Object store metrics

These track I/O against the underlying object store. The base label identifies the store; its cardinality is controlled by the LANCE_OBJECT_STORE_METRICS_LABEL environment variable:

• scheme (default) — the scheme only (s3, gs, az, file, memory); low, bounded cardinality.
• full — the store's unique prefix (s3$my-bucket, az$container@account where Azure's account also matters), so multiple buckets on the same cloud can be told apart. Cardinality grows with the number of stores accessed.
• off — omit the base label entirely.

operation is one of get, put, put_part, head, list, delete, copy, rename, complete_multipart, or abort_multipart.

Request counts are per logical operation: a list or delete that spans many objects is one request, matching how backends batch them.

Metric	Type	Labels	Description
lance_object_store_requests_total	counter	operation, base	Object store requests issued.
lance_object_store_request_bytes_total	counter	operation, base	Bytes transferred by get/put requests. A get is counted once its response body has been fully read.
lance_object_store_request_duration_seconds	histogram	operation, base	Per-request latency, in seconds. For get this covers the full body transfer, not just time-to-first-byte.
lance_object_store_errors_total	counter	operation, base	Requests that returned an error.
lance_object_store_in_flight_requests	gauge	operation, base	Requests currently in flight.
lance_object_store_throttle_total	counter	status, base	Throttle responses (HTTP 429 / 503) seen at the HTTP layer, counted per attempt including retries. The status label is the numeric HTTP status.
lance_object_store_retryable_responses_total	counter	status, base	Retryable responses (HTTP 5xx / 429 / 408) seen at the HTTP layer, counted per attempt including retries. A superset of throttle_total; 409 (conflict) is excluded so commit conflicts are not counted.

lance_object_store_throttle_total and lance_object_store_retryable_responses_total are recorded only for the native cloud stores (S3, GCS, Azure); Opendal-backed stores bypass the HTTP client where the counters are installed, so they report the other object store metrics but not throttle/retryable counts.