org.apache.accumulo.core.client.sample

Class AbstractHashSampler

java.lang.Object

org.apache.accumulo.core.client.sample.AbstractHashSampler

All Implemented Interfaces:

Sampler

Direct Known Subclasses:

RowColumnSampler, RowSampler

public abstract class AbstractHashSampler
extends Object
implements Sampler

A base class that can be used to create Samplers based on hashing. This class offers consistent options for configuring the hash function. The subclass decides which parts of the key to hash.

This class support two options passed into init(SamplerConfiguration). One option is hasher which specifies a hashing algorithm. Valid values for this option are md5, sha1, and murmur3_32. If you are not sure, then choose murmur3_32.

The second option is modulus which can have any positive integer as a value.

Any data where hash(data) % modulus == 0 will be selected for the sample.

Since:

1.8.0

Constructor Summary

Constructors

Constructor and Description
AbstractHashSampler()

Method Summary

Modifier and Type	Method and Description
boolean	accept(Key k)
protected abstract void	hash(DataOutput hasher, Key k) Subclass must override this method and hash some portion of the key.
void	init(SamplerConfiguration config) Subclasses with options should override this method and call super.init(config).
protected boolean	isValidOption(String option) Subclasses with options should override this method and return true if the option is valid for the subclass or if super.isValidOption(opt) returns true.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AbstractHashSampler

public AbstractHashSampler()

Method Detail

isValidOption

protected boolean isValidOption(String option)

Subclasses with options should override this method and return true if the option is valid for the subclass or if super.isValidOption(opt) returns true.

init

public void init(SamplerConfiguration config)

Subclasses with options should override this method and call super.init(config).

Specified by:

init in interface Sampler

Parameters:

config - Configuration options for a sampler.

hash

protected abstract void hash(DataOutput hasher,
                             Key k)
                      throws IOException

Subclass must override this method and hash some portion of the key.

Parameters:

hasher - Data written to this will be used to compute the hash for the key.

Throws:

IOException

accept

public boolean accept(Key k)

Specified by:

accept in interface Sampler

Parameters:

k - A key that was written to a rfile.

Returns:

True if the key (and its associtated value) should be stored in the rfile's sample. Return false if it should not be included.