DubboMergingDigest (Apache Dubbo 3.2.9 API)

java.lang.Object
- com.tdunning.math.stats.TDigest
- - org.apache.dubbo.metrics.aggregate.DubboAbstractTDigest
  - - org.apache.dubbo.metrics.aggregate.DubboMergingDigest

All Implemented Interfaces:

Serializable
```
public class DubboMergingDigest
extends DubboAbstractTDigest
```
Maintains a t-digest by collecting new points in a buffer that is then sorted occasionally and merged into a sorted array that contains previously computed centroids.
This can be very fast because the cost of sorting and merging is amortized over several insertion. If we keep N centroids total and have the input array is k long, then the amortized cost is something like
N/k + log k
These costs even out when N/k = log k. Balancing costs is often a good place to start in optimizing an algorithm. For different values of compression factor, the following table shows estimated asymptotic values of N and suggested values of k:

Compression N k

50 78 25

100 157 42

200 314 73

Sizing considerations for t-digest

The virtues of this kind of t-digest implementation include:
- No allocation is required after initialization
- The data structure automatically compresses existing centroids when possible
- No Java object overhead is incurred for centroids since data is kept in primitive arrays
The current implementation takes the liberty of using ping-pong buffers for implementing the merge resulting in a substantial memory penalty, but the complexity of an in place merge was not considered as worthwhile since even with the overhead, the memory cost is less than 40 bytes per centroid which is much less than half what the AVLTreeDigest uses and no dynamic allocation is required at all.
See Also:

Serialized Form

Sizing considerations for t-digest
Compression	N	k
50	78	25
100	157	42
200	314	73

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

static class DubboMergingDigest.Encoding

Nested Classes
Modifier and Type	Class and Description
`static class`	`DubboMergingDigest.Encoding`

Field Summary

Fields
Modifier and Type Field and Description

boolean useAlternatingSort

boolean useTwoLevelCompression

static boolean useWeightLimit

Fields
Modifier and Type	Field and Description
`boolean`	`useAlternatingSort`
`boolean`	`useTwoLevelCompression`
`static boolean`	`useWeightLimit`

Constructor Summary

Constructors
Constructor and Description
`DubboMergingDigest(double compression)` Allocates a buffer merging t-digest.
`DubboMergingDigest(double compression, int bufferSize)` If you know the size of the temporary buffer for incoming points, you can use this entry point.
`DubboMergingDigest(double compression, int bufferSize, int size)` Fully specified constructor.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`add(double x, int w)`
`void`	`add(List<? extends com.tdunning.math.stats.TDigest> others)`
`void`	`asBytes(ByteBuffer buf)`
`void`	`asSmallBytes(ByteBuffer buf)`
`int`	`byteSize()`
`double`	`cdf(double x)`
`int`	`centroidCount()`
`Collection<com.tdunning.math.stats.Centroid>`	`centroids()`
`void`	`compress()` Merges any pending inputs and compresses the data down to the public setting.
`double`	`compression()`
`double`	`getMax()`
`double`	`getMin()`
`com.tdunning.math.stats.ScaleFunction`	`getScaleFunction()`
`double`	`quantile(double q)`
`com.tdunning.math.stats.TDigest`	`recordAllData()` Turns on internal data recording.
`void`	`setScaleFunction(com.tdunning.math.stats.ScaleFunction scaleFunction)`
`long`	`size()`
`int`	`smallByteSize()`
`String`	`toString()`

Methods inherited from class org.apache.dubbo.metrics.aggregate.DubboAbstractTDigest
add, add, isRecording

Methods inherited from class com.tdunning.math.stats.TDigest
createAvlTreeDigest, createDigest, createMergingDigest

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

- Field Detail
  - useAlternatingSort
```
public boolean useAlternatingSort
```
  - useTwoLevelCompression
```
public boolean useTwoLevelCompression
```
  - useWeightLimit
```
public static boolean useWeightLimit
```
- Constructor Detail
  - DubboMergingDigest
```
public DubboMergingDigest(double compression)
```
    Allocates a buffer merging t-digest. This is the normally used constructor that allocates default sized internal arrays. Other versions are available, but should only be used for special cases.
    
    Parameters:
    
    compression - The compression factor
  - DubboMergingDigest
```
public DubboMergingDigest(double compression,
                          int bufferSize)
```
    If you know the size of the temporary buffer for incoming points, you can use this entry point.
    
    Parameters:
    
    compression - Compression factor for t-digest. Same as 1/\delta in the paper.
    
    bufferSize - How many samples to retain before merging.
  - DubboMergingDigest
```
public DubboMergingDigest(double compression,
                          int bufferSize,
                          int size)
```
    Fully specified constructor. Normally only used for deserializing a buffer t-digest.
    
    Parameters:
    
    compression - Compression factor
    
    bufferSize - Number of temporary centroids
    
    size - Size of main buffer
- Method Detail
  - getMin
```
public double getMin()
```
    Overrides:
    
    getMin in class com.tdunning.math.stats.TDigest
  - getMax
```
public double getMax()
```
    Overrides:
    
    getMax in class com.tdunning.math.stats.TDigest
  - recordAllData
```
public com.tdunning.math.stats.TDigest recordAllData()
```
    Turns on internal data recording.
    
    Overrides:
    
    recordAllData in class DubboAbstractTDigest
  - add
```
public void add(double x,
                int w)
```
    Specified by:
    
    add in class com.tdunning.math.stats.TDigest
  - add
```
public void add(List<? extends com.tdunning.math.stats.TDigest> others)
```
    Specified by:
    
    add in class com.tdunning.math.stats.TDigest
  - compress
```
public void compress()
```
    Merges any pending inputs and compresses the data down to the public setting. Note that this typically loses a bit of precision and thus isn't a thing to be doing all the time. It is best done only when we want to show results to the outside world.
    
    Specified by:
    
    compress in class com.tdunning.math.stats.TDigest
  - size
```
public long size()
```
    Specified by:
    
    size in class com.tdunning.math.stats.TDigest
  - cdf
```
public double cdf(double x)
```
    Specified by:
    
    cdf in class com.tdunning.math.stats.TDigest
  - quantile
```
public double quantile(double q)
```
    Specified by:
    
    quantile in class com.tdunning.math.stats.TDigest
  - centroidCount
```
public int centroidCount()
```
    Specified by:
    
    centroidCount in class com.tdunning.math.stats.TDigest
  - centroids
```
public Collection<com.tdunning.math.stats.Centroid> centroids()
```
    Specified by:
    
    centroids in class com.tdunning.math.stats.TDigest
  - compression
```
public double compression()
```
    Specified by:
    
    compression in class com.tdunning.math.stats.TDigest
  - byteSize
```
public int byteSize()
```
    Specified by:
    
    byteSize in class com.tdunning.math.stats.TDigest
  - smallByteSize
```
public int smallByteSize()
```
    Specified by:
    
    smallByteSize in class com.tdunning.math.stats.TDigest
  - getScaleFunction
```
public com.tdunning.math.stats.ScaleFunction getScaleFunction()
```
  - setScaleFunction
```
public void setScaleFunction(com.tdunning.math.stats.ScaleFunction scaleFunction)
```
    Overrides:
    
    setScaleFunction in class com.tdunning.math.stats.TDigest
  - asBytes
```
public void asBytes(ByteBuffer buf)
```
    Specified by:
    
    asBytes in class com.tdunning.math.stats.TDigest
  - asSmallBytes
```
public void asSmallBytes(ByteBuffer buf)
```
    Specified by:
    
    asSmallBytes in class com.tdunning.math.stats.TDigest
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object

Class DubboMergingDigest

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class org.apache.dubbo.metrics.aggregate.DubboAbstractTDigest

Methods inherited from class com.tdunning.math.stats.TDigest

Methods inherited from class java.lang.Object

Field Detail

useAlternatingSort

useTwoLevelCompression

useWeightLimit

Constructor Detail

DubboMergingDigest

DubboMergingDigest

DubboMergingDigest

Method Detail

getMin

getMax

recordAllData

add

add

compress

size

cdf

quantile

centroidCount

centroids

compression

byteSize

smallByteSize

getScaleFunction

setScaleFunction

asBytes

asSmallBytes

toString