Class ExemplarLabelsSupplier

Object
ExemplarLabelsSupplier
@StableApi public class ExemplarLabelsSupplier extends Object
Global holder for a Supplier of additional Labels that are merged into every automatically-sampled Exemplar across the entire application.

This is the global counterpart to the per-metric exemplarLabelsSupplier(...) builder method. Registering a supplier here affects all metrics, including metrics registered by third-party libraries that the application does not control. This makes it the right tool when you cannot modify the code that creates the metrics.

The supplier is invoked on the metric hot path (rate-limited by the exemplar sampler), each time an Exemplar is sampled from a valid, sampled span context. It should therefore be cheap and non-blocking. It may return dynamic, request-scoped values, for example an identifier read from a thread-local: 

ExemplarLabelsSupplier.setExemplarLabelsSupplier(
    () -> Labels.of("management_id", currentManagementId()));

Labels returned by the supplier that collide with trace_id/span_id (or, when a per-metric supplier is also configured, with that supplier's labels) are silently dropped rather than causing an error: the per-metric supplier takes precedence over the global one, and the reserved trace_id/span_id labels always win. If the supplier throws, the exception is swallowed and the Exemplar is created without the additional labels, so a misbehaving supplier never breaks metric collection.