Load required subfields only for aggregate_metric_double #136084
Description
Description
The AggregateMetricDoubleBlock is a composite block that consists of 4 blocks representing the 4 values that it could potentially consist of min, max, sum, value_count.
Currently, when the AggregateMetricDoubleFieldMapper loads a block for ES|QL is loads all 4 blocks without taking into consideration which blocks are needed for the query. This is what we want to change. We would like to analyse an ES|QL query and only load the blocks that are needed to respond to this query.
Notes:
Something similar is being done in GeoShapeWithDocValuesFieldMapper which uses the BlockLoaderContext to inform the respective mapper on what to load. It might be a good place to start looking.