To use this aggregator, make sure you include the extension in your config file:

HLLSketchBuild Aggregator

  1. {
  3.   "name" : <output name>,
  4.   "lgK" : <size and accuracy parameter>,
  5.   "tgtHllType" : <target HLL type>,
  6.   "round": <false | true>
  7.  }

It is very common to use HLLSketchBuild in combination with rollup to create a on high-cardinality columns. In this example, a metric called userid_hll is included in the metricsSpec. This will perform a HLL sketch on the userid field at ingestion time, allowing for highly-performant approximate COUNT DISTINCT query operations and improving roll-up ratios when userid is then left out of the dimensionsSpec.

HLLSketchMerge Aggregator

  1. {
  2.   "type" : "HLLSketchMerge",
  4.   "fieldName" : <metric name>,
  5.   "lgK" : <size and accuracy parameter>,
  6.   "tgtHllType" : <target HLL type>,
  7.  }

Post Aggregators

Estimate

Estimate with bounds

Returns a distinct count estimate and error bounds from an HLL sketch. The result will be an array containing three double values: estimate, lower bound and upper bound. The bounds are provided at a given number of standard deviations (optional, defaults to 1). This must be an integer value of 1, 2 or 3 corresponding to approximately 68.3%, 95.4% and 99.7% confidence intervals.

  1. {
  2.   "type"  : "HLLSketchEstimateWithBounds",
  3.   "name": <output name>,
  4.   "field"  : <post aggregator that returns an HLL Sketch>,
  5.   "numStdDev" : <number of standard deviations: 1 (default), 2 or 3>
  6. }

Union

Sketch to string

  1. {
  2.   "type"  : "HLLSketchToString",
  3.   "name": <output name>,