simpledb

Class StringHistogram

java.lang.Object

simpledb.StringHistogram

public class StringHistogram
extends java.lang.Object

A class to represent a fixed-width histogram over a single String-based field.

Field Summary

Fields

Modifier and Type	Field and Description
(package private) IntHistogram	hist

Constructor Summary

Constructors

Constructor and Description
StringHistogram(int buckets) Create a new StringHistogram with a specified number of buckets.

Method Summary

Modifier and Type	Method and Description
void	addValue(java.lang.String s) Add a new value to thte histogram
double	avgSelectivity()
double	estimateSelectivity(Predicate.Op op, java.lang.String s) Estimate the selectivity (as a double between 0 and 1) of the specified predicate over the specified string
(package private) int	maxVal()
(package private) int	minVal()
private int	stringToInt(java.lang.String s)

Methods inherited from class java.lang.Object

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

Field Detail

hist

IntHistogram hist

Constructor Detail

StringHistogram

public StringHistogram(int buckets)

Create a new StringHistogram with a specified number of buckets.

Our implementation is written in terms of an IntHistogram by converting each String to an integer.

Parameters:

buckets - the number of buckets

Method Detail

stringToInt

private int stringToInt(java.lang.String s)

maxVal

int maxVal()

Returns:

the maximum value indexed by the histogram

minVal

int minVal()

Returns:

the minimum value indexed by the histogram

addValue

public void addValue(java.lang.String s)

Add a new value to thte histogram

estimateSelectivity

public double estimateSelectivity(Predicate.Op op,
                                  java.lang.String s)

Estimate the selectivity (as a double between 0 and 1) of the specified predicate over the specified string

Parameters:

op - The operation being applied

s - The string to apply op to

avgSelectivity

public double avgSelectivity()

Returns:

the average selectivity of this histogram. This is not an indispensable method to implement the basic join optimization. It may be needed if you want to implement a more efficient optimization