DistributedRandomSampler (Flink : Java 1.20.1-cp2 API)

java.lang.Object
- org.apache.flink.api.java.sampling.RandomSampler<T>
- - org.apache.flink.api.java.sampling.DistributedRandomSampler<T>

Type Parameters:

T - The input data type.

Direct Known Subclasses:

ReservoirSamplerWithoutReplacement, ReservoirSamplerWithReplacement
```
@Internal
public abstract class DistributedRandomSampler<T>
extends RandomSampler<T>
```
For sampling with fraction, the sample algorithms are natively distributed, while it's not true for fixed size sample algorithms. The fixed size sample algorithms require two-phases sampling (according to our current implementation). In the first phase, each distributed partition is sampled independently. The partial sampling results are handled by a central coordinator. The central coordinator combines the partial sampling results to form the final result.

Field Summary

Fields
Modifier and Type Field Description

protected Iterator<IntermediateSampleData<T>> emptyIntermediateIterable

protected int numSamples
- Fields inherited from class org.apache.flink.api.java.sampling.RandomSampler
  emptyIterable, EPSILON

Constructor Summary

Constructors
Constructor Description

DistributedRandomSampler(int numSamples)

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`Iterator<T>`	`sample(Iterator<T> input)`	Combine the first phase and second phase in sequence, implemented for test purpose only.
`Iterator<T>`	`sampleInCoordinator(Iterator<IntermediateSampleData<T>> input)`	Sample algorithm for the second phase.
`abstract Iterator<IntermediateSampleData<T>>`	`sampleInPartition(Iterator<T> input)`	Sample algorithm for the first phase.

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

- Field Detail
  - numSamples
```
protected final int numSamples
```
  - emptyIntermediateIterable
```
protected final Iterator<IntermediateSampleData<T>> emptyIntermediateIterable
```
- Constructor Detail
  - DistributedRandomSampler
```
public DistributedRandomSampler(int numSamples)
```
- Method Detail
  - sampleInPartition
```
public abstract Iterator<IntermediateSampleData<T>> sampleInPartition(Iterator<T> input)
```
    Sample algorithm for the first phase. It operates on a single partition.
    
    Parameters:
    
    input - The DataSet input of each partition.
    
    Returns:
    
    Intermediate sample output which will be used as the input of the second phase.
  - sampleInCoordinator
```
public Iterator<T> sampleInCoordinator(Iterator<IntermediateSampleData<T>> input)
```
    Sample algorithm for the second phase. This operation should be executed as the UDF of an all reduce operation.
    
    Parameters:
    
    input - The intermediate sample output generated in the first phase.
    
    Returns:
    
    The sampled output.
  - sample
```
public Iterator<T> sample(Iterator<T> input)
```
    Combine the first phase and second phase in sequence, implemented for test purpose only.
    
    Specified by:
    
    sample in class RandomSampler<T>
    
    Parameters:
    
    input - Source data.
    
    Returns:
    
    Sample result in sequence.