org.apache.hadoop.util.bloom
Class CountingBloomFilter

java.lang.Object
  org.apache.hadoop.util.bloom.Filter
      org.apache.hadoop.util.bloom.CountingBloomFilter

All Implemented Interfaces:

Writable

public final class CountingBloomFilter
extends Filter

Implements a counting Bloom filter, as defined by Fan et al. in a ToN 2000 paper.

A counting Bloom filter is an improvement to standard a Bloom filter as it allows dynamic additions and deletions of set membership information. This is achieved through the use of a counting vector instead of a bit vector.

Originally created by European Commission One-Lab Project 034819.

See Also:

The general behavior of a filter, Summary cache: a scalable wide-area web cache sharing protocol

Field Summary

Fields inherited from class org.apache.hadoop.util.bloom.Filter

hash, hashType, nbHash, vectorSize

Constructor Summary

CountingBloomFilter()
Default constructor - use with readFields

CountingBloomFilter(int vectorSize, int nbHash, int hashType)
Constructor

Method Summary

void	add(Key key) Adds a key to this filter.
void	and(Filter filter) Peforms a logical AND between this filter and a specified filter.
int	approximateCount(Key key) This method calculates an approximate count of the key, i.e.
void	delete(Key key) Removes a specified key from this counting Bloom filter.
boolean	membershipTest(Key key) Determines wether a specified key belongs to this filter.
void	not() Performs a logical NOT on this filter.
void	or(Filter filter) Peforms a logical OR between this filter and a specified filter.
void	readFields(DataInput in) Deserialize the fields of this object from in.
String	toString()
void	write(DataOutput out) Serialize the fields of this object to out.
void	xor(Filter filter) Peforms a logical XOR between this filter and a specified filter.

Methods inherited from class org.apache.hadoop.util.bloom.Filter

add, add, add

Methods inherited from class java.lang.Object

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

Constructor Detail

CountingBloomFilter

public CountingBloomFilter()

Default constructor - use with readFields

CountingBloomFilter

public CountingBloomFilter(int vectorSize,
                           int nbHash,
                           int hashType)

Constructor

Parameters:

vectorSize - The vector size of this filter.

nbHash - The number of hash function to consider.

hashType - type of the hashing function (see Hash).

Method Detail

add

public void add(Key key)

Description copied from class: Filter

Adds a key to this filter.

Specified by:

add in class Filter

Parameters:

key - The key to add.

delete

public void delete(Key key)

Removes a specified key from this counting Bloom filter.

Invariant: nothing happens if the specified key does not belong to this counter Bloom filter.

Parameters:

key - The key to remove.

and

public void and(Filter filter)

Description copied from class: Filter

Peforms a logical AND between this filter and a specified filter.

Invariant: The result is assigned to this filter.

Specified by:

and in class Filter

Parameters:

filter - The filter to AND with.

membershipTest

public boolean membershipTest(Key key)

Description copied from class: Filter

Determines wether a specified key belongs to this filter.

Specified by:

membershipTest in class Filter

Parameters:

key - The key to test.

Returns:

boolean True if the specified key belongs to this filter. False otherwise.

approximateCount

public int approximateCount(Key key)

This method calculates an approximate count of the key, i.e. how many times the key was added to the filter. This allows the filter to be used as an approximate key -> count map.

NOTE: due to the bucket size of this filter, inserting the same key more than 15 times will cause an overflow at all filter positions associated with this key, and it will significantly increase the error rate for this and other keys. For this reason the filter can only be used to store small count values 0 <= N << 15.

Parameters:

key - key to be tested

Returns:

0 if the key is not present. Otherwise, a positive value v will be returned such that v == count with probability equal to the error rate of this filter, and v > count otherwise. Additionally, if the filter experienced an underflow as a result of delete(Key) operation, the return value may be lower than the count with the probability of the false negative rate of such filter.

not

public void not()

Description copied from class: Filter

Performs a logical NOT on this filter.

The result is assigned to this filter.

Specified by:

not in class Filter

or

public void or(Filter filter)

Description copied from class: Filter

Peforms a logical OR between this filter and a specified filter.

Invariant: The result is assigned to this filter.

Specified by:

or in class Filter

Parameters:

filter - The filter to OR with.

xor

public void xor(Filter filter)

Description copied from class: Filter

Peforms a logical XOR between this filter and a specified filter.

Invariant: The result is assigned to this filter.

Specified by:

xor in class Filter

Parameters:

filter - The filter to XOR with.

toString

public String toString()

Overrides:

toString in class Object

write

public void write(DataOutput out)
           throws IOException

Description copied from interface: Writable

Serialize the fields of this object to out.

Specified by:

write in interface Writable

Overrides:

write in class Filter

Parameters:

out - DataOuput to serialize this object into.

Throws:

IOException

readFields

public void readFields(DataInput in)
                throws IOException

Description copied from interface: Writable

Deserialize the fields of this object from in.

For efficiency, implementations should attempt to re-use storage in the existing object where possible.

Specified by:

readFields in interface Writable

Overrides:

readFields in class Filter

Parameters:

in - DataInput to deseriablize this object from.

Throws:

IOException