diff --git a/CHANGELOG.md b/CHANGELOG.md index 5dd11bd6ca2..3eff87a349d 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -44,7 +44,7 @@ The next release will require at least [Go 1.24]. - `RPCGRPCResponseMetadata` - Add `ErrorType` attribute helper function to the `go.opentelmetry.io/otel/semconv/v1.34.0` package. (#6962) - Add `WithAllowKeyDuplication` in `go.opentelemetry.io/otel/sdk/log` which can be used to disable deduplication for log records. (#6968) -- Add `WithCardinalityLimit` option to configure the cardinality limit in `go.opentelemetry.io/otel/sdk/metric`. (#6996, #7065, #7081, #7164, #7165) +- Add `WithCardinalityLimit` option to configure the cardinality limit in `go.opentelemetry.io/otel/sdk/metric`. (#6996, #7065, #7081, #7164, #7165, #7179) - Add `Clone` method to `Record` in `go.opentelemetry.io/otel/log` that returns a copy of the record with no shared state. (#7001) - The `go.opentelemetry.io/otel/semconv/v1.36.0` package. The package contains semantic conventions from the `v1.36.0` version of the OpenTelemetry Semantic Conventions. diff --git a/sdk/metric/doc.go b/sdk/metric/doc.go index 90a4ae16c1a..5f8cfd58d50 100644 --- a/sdk/metric/doc.go +++ b/sdk/metric/doc.go @@ -39,6 +39,30 @@ // Meter.RegisterCallback and Registration.Unregister to add and remove // callbacks without leaking memory. // +// # Cardinality Limits +// +// Cardinality refers to the number of unique attributes collected. High cardinality can lead to +// excessive memory usage, increased storage costs, and backend performance issues. +// +// Currently, the OpenTelemetry Go Metric SDK does not enforce a cardinality limit by default +// (note that this may change in a future release). Use [WithCardinalityLimit] to set the +// cardinality limit as desired. +// +// New attribute sets are dropped when the cardinality limit is reached. The measurement of +// these sets are aggregated into +// a special attribute set containing "otel.metric.overflow" attribute with "true" value. +// This ensures total metric values (e.g., Sum, Count) remain correct for the +// collection cycle, but information about the specific dropped sets +// is not preserved. +// +// Recommendations: +// +// - Set the limit based on the theoretical maximum combinations or expected +// active combinations. The OpenTelemetry Specification recommends a default of 2000. +// - A too high of a limit increases worst-case memory overhead in the SDK and may cause downstream +// issues for databases that cannot handle high cardinality. +// - A too low of a limit causes loss of attribute detail as more data falls into overflow. +// // See [go.opentelemetry.io/otel/metric] for more information about // the metric API. //