DataSketches HLL Sketch module

    2.   "type" : "HLLSketchBuild",
    3.   "fieldName" : <metric name>,
    4.   "lgK" : <size and accuracy parameter>,
    5.   "tgtHllType" : <target HLL type>,
    6.   "round": <false | true>

    Post Aggregators

    Estimate

    1. {
    2.   "type"  : "HLLSketchEstimate",
    3.   "name": <output name>,
    4.   "round" : <if true, round the estimate. Default is false>
    5. }

    Estimate with bounds

    Union

    2.   "type"  : "HLLSketchUnion",
    3.   "name": <output name>,
    4.   "fields"  : <array of post aggregators that return HLL sketches>,
    5.   "lgK": <log2 of K for the target sketch>,
    6.   "tgtHllType" : <target HLL type>

    Sketch to string