io.prestosql.operator.aggregation.histogram

Class HashUtil

java.lang.Object

io.prestosql.operator.aggregation.histogram.HashUtil

public class HashUtil
extends Object

Method Summary

Modifier and Type	Method and Description
static int	calculateMaxFill(int bucketCount, float fillRatio)
static int	computeBucketCount(int expectedSize, float fillRatio) uses HashCommon.arraySize() which does this calculation.
static int	nextBucketId(int bucketId, int mask, int probe)
static int	nextProbeLinear(int probeCount)
static int	nextSumOfCount(int probeCount)
static int	nextSumOfSquares(int probeCount)

Methods inherited from class java.lang.Object

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

Method Detail

nextProbeLinear

public static int nextProbeLinear(int probeCount)

nextSumOfCount

public static int nextSumOfCount(int probeCount)

nextSumOfSquares

public static int nextSumOfSquares(int probeCount)

nextBucketId

public static int nextBucketId(int bucketId,
                               int mask,
                               int probe)

Parameters:

bucketId - - previous bucketId location

mask - - mask being used (typically # of buckets-1; due to power-of-2 sized bucket arrays, handles wrap-around

probe - - how many buckets to jump to find next bucket

Returns:

next bucketId, including any necessary wrap-around (again mask handles this)

calculateMaxFill

public static int calculateMaxFill(int bucketCount,
                                   float fillRatio)

computeBucketCount

public static int computeBucketCount(int expectedSize,
                                     float fillRatio)

uses HashCommon.arraySize() which does this calculation. this is just a wrapper to name the use of this case

Parameters:

expectedSize - - expected number of elements to store in the hash

fillRatio - - expected fill ratio of buckets by elemements

Returns:

nextPowerOfTwo(expectedSize / fillRatio)