Motivation

The LoggingEmitter currently emits all metrics it receives without filtering. On busy clusters with high query throughput, this can result in a very large volume of metric logs - on some of our clusters, we've seen ~3M metric logs in 15 minutes.

Proposed changes

• Add a file to capture the default metrics for the LoggingEmitter, similar to the Prometheus and Dropwizard emitters (e.g., defaultMetricDimensions.json).
• This file can contain the list of allowed metrics.
• In the future, we can extend this file to annotate additional user-defined dimensions, if needed.
• In the LoggingEmitter emit(Event event) method, check the allowlist metrics map and decide whether to include the event or not.

Rationale

Typically, the LoggingEmitter is used in conjunction with a composite emitter that handles low- to medium-cardinality metrics, such as Prometheus, Dropwizard, or Kafka forwarding to a downstream system. Filtering out metrics that are already covered by these emitters would help reduce logging costs while continuing to rely on the appropriate emitter for low- to medium-cardinality metrics.

Operational impact

None. By default, all metrics will continue to be emitted for backwards compatibility with a runtime property. Operators can opt-in to enable filtering with the property.