HyperLogLogPlusPlus (Flink : 2.0-preview1 API)

java.lang.Object
- org.apache.flink.table.runtime.functions.aggregate.hyperloglog.HyperLogLogPlusPlus

```
public class HyperLogLogPlusPlus
extends Object
```
The implement of HyperLogLogPlusPlus is inspired from Apache Spark.

Constructor Summary

Constructors
Constructor Description

HyperLogLogPlusPlus(double relativeSD)

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`double`	`estimateBias(double e)`	Estimate the bias using the raw estimates with their respective biases from the HLL++ appendix.
`int`	`getNumWords()`
`void`	`merge(HllBuffer buffer1, HllBuffer buffer2)`	Merge the HLL buffers by iterating through the registers in both buffers and select the maximum number of leading zeros for each register.
`long`	`query(HllBuffer buffer)`	Compute the HyperLogLog estimate.
`double`	`trueRsd()`	The `rsd` of HLL++ is always equal to or better than the `rsd` requested.
`void`	`updateByHashcode(HllBuffer buffer, long hash)`	Update the HLL++ buffer.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - HyperLogLogPlusPlus
```
public HyperLogLogPlusPlus(double relativeSD)
```
- Method Detail
  - getNumWords
```
public int getNumWords()
```
  - updateByHashcode
```
public void updateByHashcode(HllBuffer buffer,
                             long hash)
```
    Update the HLL++ buffer.
  - merge
```
public void merge(HllBuffer buffer1,
                  HllBuffer buffer2)
```
    Merge the HLL buffers by iterating through the registers in both buffers and select the maximum number of leading zeros for each register.
  - estimateBias
```
public double estimateBias(double e)
```
    Estimate the bias using the raw estimates with their respective biases from the HLL++ appendix. We currently use KNN interpolation to determine the bias (as suggested in the paper).
  - query
```
public long query(HllBuffer buffer)
```
    Compute the HyperLogLog estimate.
    Variable names in the HLL++ paper match variable names in the code.
  - trueRsd
```
public double trueRsd()
```
    The rsd of HLL++ is always equal to or better than the rsd requested. This method returns the rsd this instance actually guarantees.
    
    Returns:
    
    the actual rsd.