com.facebook.presto.operator.aggregation.approxmostfrequent

Class ApproximateMostFrequent

java.lang.Object

com.facebook.presto.metadata.BuiltInFunction

com.facebook.presto.metadata.SqlAggregationFunction

com.facebook.presto.operator.aggregation.approxmostfrequent.ApproximateMostFrequent

All Implemented Interfaces:

SqlFunction

public final class ApproximateMostFrequent
extends SqlAggregationFunction

Aggregation function that computes the top-K frequent elements approximately. Approximate estimation of the function enables us to pick up the frequent values with less memory. Larger input "capacity" improves the accuracy of underlying algorithm with sacrificing the memory capacity.

The algorithm is based loosely on: Efficient Computation of Frequent and Top-*k* Elements in Data Streams by Ahmed Metwally, Divyakant Agrawal, and Amr El Abbadi

Field Summary

Fields

Modifier and Type	Field and Description
static ApproximateMostFrequent	APPROXIMATE_MOST_FREQUENT
static String	NAME

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ApproximateMostFrequent()

Method Summary

Modifier and Type	Method and Description
static void	combine(ApproximateMostFrequentState state, ApproximateMostFrequentState otherState)
String	getDescription()
static void	input(Type type, ApproximateMostFrequentState state, long buckets, Block valueBlock, int valueIndex, long capacity)
static void	output(ApproximateMostFrequentState state, BlockBuilder out)
BuiltInAggregationFunctionImplementation	specialize(BoundVariables boundVariables, int arity, FunctionAndTypeManager functionAndTypeManager)

Methods inherited from class com.facebook.presto.metadata.SqlAggregationFunction

createFunctionByAnnotations, createFunctionsByAnnotations, getSignature, getVisibility, isDeterministic

Methods inherited from class com.facebook.presto.metadata.BuiltInFunction

isCalledOnNullInput

Methods inherited from class java.lang.Object

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

Field Detail

APPROXIMATE_MOST_FREQUENT

public static final ApproximateMostFrequent APPROXIMATE_MOST_FREQUENT

NAME

public static final String NAME

See Also:

Constant Field Values

Constructor Detail

ApproximateMostFrequent

protected ApproximateMostFrequent()

Method Detail

specialize

public BuiltInAggregationFunctionImplementation specialize(BoundVariables boundVariables,
                                                           int arity,
                                                           FunctionAndTypeManager functionAndTypeManager)

Specified by:

specialize in class SqlAggregationFunction

getDescription

public String getDescription()

input

public static void input(Type type,
                         ApproximateMostFrequentState state,
                         long buckets,
                         Block valueBlock,
                         int valueIndex,
                         long capacity)

combine

public static void combine(ApproximateMostFrequentState state,
                           ApproximateMostFrequentState otherState)

output

public static void output(ApproximateMostFrequentState state,
                          BlockBuilder out)