StableMetric ExemplarReservoir return empty data points

[bryce-b]

Summary

When an exemplar reservoir's collectAndReset method is called, no care is taken to verify which cells are populated, thus empty exemplar datapoints are returned in the array.

opentelemetry-swift/Sources/OpenTelemetrySdk/Metrics/Stable/Exemplar/ExemplarReservoir.swift

Line 43 in 7125823

public class FixedSizedExemplarReservoir: ExemplarReservoir {

Detail

The storage is initialized with size number of ReservoirCell.

But the buckets have default values, and are only populated when offer measurement is called:

If any cell has measurements, the method will return results from all cells, even if they haven't been populated.

[bryce-b]

The Java sdk uses the ReservoirCell getAndResetDouble or getAndResetLong for this method, which will return null if attributes is unset.
https://github.com/open-telemetry/opentelemetry-java/blob/main/sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/exemplar/ReservoirCell.java#L105

[bryce-b]

mistakenly closed this issue