Module org.elasticsearch.exponentialhistogram
Package org.elasticsearch.exponentialhistogram

Class ExponentialScaleUtils

java.lang.Object
org.elasticsearch.exponentialhistogram.ExponentialScaleUtils
public class ExponentialScaleUtils extends Object
A collection of utility methods for working with indices and scales of exponential bucket histograms.

  • Constructor Details

    • ExponentialScaleUtils

      public ExponentialScaleUtils()

  • Method Details

    • compareExponentiallyScaledValues

      public static int compareExponentiallyScaledValues(long idxA, int scaleA, long idxB, int scaleB)
      Compares the lower boundaries of two buckets, which may have different scales. This is equivalent to a mathematically correct comparison of the lower bucket boundaries. Note that this method allows for scales and indices of the full numeric range of the types.
      Parameters:
      idxA - the index of the first bucket
      scaleA - the scale of the first bucket
      idxB - the index of the second bucket
      scaleB - the scale of the second bucket
      Returns:
      a negative integer, zero, or a positive integer as the first bucket's lower boundary is less than, equal to, or greater than the second bucket's lower boundary

    • getMaximumScaleIncrease

      public static int getMaximumScaleIncrease(long index)
      Returns the maximum permissible scale increase that does not cause the index to grow out of the [ExponentialHistogram.MIN_INDEX, ExponentialHistogram.MIN_INDEX] range.
      Parameters:
      index - the index to check
      Returns:
      the maximum permissible scale increase

    • getUpperBucketBoundary

      public static double getUpperBucketBoundary(long index, int scale)
      Returns the upper boundary of the bucket with the given index and scale.
      Parameters:
      index - the index of the bucket
      scale - the scale of the bucket
      Returns:
      the upper boundary of the bucket

    • getLowerBucketBoundary

      public static double getLowerBucketBoundary(long index, int scale)
      Returns the lower boundary of the bucket with the given index and scale.
      Parameters:
      index - the index of the bucket in the [ExponentialHistogram.MIN_INDEX, ExponentialHistogram.MAX_INDEX] range.
      scale - the scale of the bucket
      Returns:
      the lower boundary of the bucket

    • getPointOfLeastRelativeError

      public static double getPointOfLeastRelativeError(long bucketIndex, int scale)
      For a bucket with the given index, computes the point x in the bucket such that (x - l) / l equals (u - x) / u, where l is the lower bucket boundary and u is the upper bucket boundary.
      In other words, we select the point in the bucket that has the least relative error with respect to any other point in the bucket.
      Parameters:
      bucketIndex - the index of the bucket
      scale - the scale of the bucket
      Returns:
      the point of least relative error

    • computeIndex

      public static long computeIndex(double value, int scale)
      Provides the index of the bucket of the exponential histogram with the given scale that contains the provided value.
      Parameters:
      value - the value to find the bucket for
      scale - the scale of the histogram
      Returns:
      the index of the bucket