sum/min/max/avg over a numeric field: bleve folds the accumulators from doc values, OpenSearch reads them from a stats aggregation, the service layer reduces them to the value of the kind after the cross-space merge. The proto gains MetricDefinition, MetricKind and Metric, which travels as accumulators (sum, count, min, max) so the merge works whatever the kind; value is set after the merge and absent for a metric without a single value. A metric is only valid on a numeric field, and only one of bucketDefinition and metricDefinition at a time. AGG-06, 18 and 21 in the parity suite.
Dominik Schmidt
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