org.tikv.common.statistics

Class Histogram

java.lang.Object

org.tikv.common.statistics.Histogram

public class Histogram
extends Object

Histogram represents core statistics for a column or index.

Each Histogram will have at most 256 buckets, each bucket contains a lower bound, a upper bound and the number of rows contain in such bound. With this information, SQL layer will be able to estimate how many rows will a index scan selects and determine which index to use will have the lowest cost.

See Also:

for moreinformation on the core data structure.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Histogram.Builder

Method Summary

Modifier and Type	Method and Description
List<Bucket>	getBuckets()
long	getId()
long	getLastUpdateVersion()
long	getNullCount()
long	getNumberOfDistinctValue()
double	lessAndEqRowCount(Key values) lessAndEqRowCount estimates the row count where the column less than or equal to value.
void	mergeBlock(int bucketIdx) mergeBuckets is used to merge every two neighbor buckets.
static Histogram.Builder	newBuilder()
String	toString()
double	totalRowCount()

Methods inherited from class java.lang.Object

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

Method Detail

newBuilder

public static Histogram.Builder newBuilder()

getNumberOfDistinctValue

public long getNumberOfDistinctValue()

getBuckets

public List<Bucket> getBuckets()

getNullCount

public long getNullCount()

getLastUpdateVersion

public long getLastUpdateVersion()

getId

public long getId()

lessAndEqRowCount

public double lessAndEqRowCount(Key values)

lessAndEqRowCount estimates the row count where the column less than or equal to value.

totalRowCount

public double totalRowCount()

mergeBlock

public void mergeBlock(int bucketIdx)

mergeBuckets is used to merge every two neighbor buckets.

Parameters:

bucketIdx: - index of the last bucket.

toString

public String toString()

Overrides:

toString in class Object