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Added percentile of partition sizes and sstables
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Cameron Zemek
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Aug 8, 2018
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,180 @@ | ||
| package com.instaclustr.sstabletools; | ||
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| import java.util.Arrays; | ||
| import java.util.Random; | ||
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| /** | ||
| * Implements a histogram using Algorithm R by Jeffrey Vitter. See https://en.wikipedia.org/wiki/Reservoir_sampling | ||
| */ | ||
| public class Histogram { | ||
| /** | ||
| * Default sampling size. | ||
| */ | ||
| private static final int DEFAULT_SIZE = 1028; | ||
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| /** | ||
| * Number of values recorded. | ||
| */ | ||
| protected int count = 0; | ||
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| /** | ||
| * Reservoir of values as per the Algorithm R. | ||
| */ | ||
| protected long[] reservoir; | ||
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| /** | ||
| * Random index generator. | ||
| */ | ||
| protected final Random random = new Random(); | ||
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| /** | ||
| * The minimum value recorded. | ||
| */ | ||
| protected long min = Long.MAX_VALUE; | ||
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| /** | ||
| * The maximum value recorded. | ||
| */ | ||
| protected long max = 0; | ||
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| /** | ||
| * The total of all values. | ||
| */ | ||
| protected long total = 0; | ||
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| public Histogram() { | ||
| this(DEFAULT_SIZE); | ||
| } | ||
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| public Histogram(int sampleSize) { | ||
| this.reservoir = new long[sampleSize]; | ||
| } | ||
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| /** | ||
| * Count of values recorded. | ||
| * | ||
| * @return number of values recorded | ||
| */ | ||
| public int getCount() { | ||
| return count; | ||
| } | ||
|
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| /** | ||
| * Update histogram with a value. | ||
| * | ||
| * @param value value to add | ||
| */ | ||
| public void update(long value) { | ||
| if (count < reservoir.length) { | ||
| // fill the reservoir array | ||
| reservoir[count] = value; | ||
| } else { | ||
| // replace elements with gradually decreasing probability | ||
| int i = random.nextInt(count + 1); | ||
| if (i < reservoir.length) { | ||
| reservoir[i] = value; | ||
| } | ||
| } | ||
| count++; | ||
| total += value; | ||
| min = Math.min(value, min); | ||
| max = Math.max(value, max); | ||
| } | ||
|
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| /** | ||
| * Snapshot histogram. | ||
| */ | ||
| public void snapshot() { | ||
| Arrays.sort(reservoir); | ||
| } | ||
|
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| /** | ||
| * Get the minimum value. | ||
| * | ||
| * @return the minimum value. | ||
| */ | ||
| public long getMin() { | ||
| return min; | ||
| } | ||
|
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| /** | ||
| * Get the maximum value. | ||
| * | ||
| * @return the maximum value. | ||
| */ | ||
| public long getMax() { | ||
| return max; | ||
| } | ||
|
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| /** | ||
| * Returns the average value. | ||
| * | ||
| * @return the average value | ||
| */ | ||
| public double getMean() { | ||
| return total / (double) count; | ||
| } | ||
|
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| /** | ||
| * Get the total of recorded values. | ||
| * | ||
| * @return the total of all values | ||
| */ | ||
| public long getTotal() { | ||
| return total; | ||
| } | ||
|
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| /** | ||
| * Returns the value at the given quantile. | ||
| * | ||
| * Snapshot histogram before calling this method. | ||
| * | ||
| * @param quantile a given quantile, in {@code [0..1]} | ||
| * @return the value in the distribution at {@code quantile} | ||
| */ | ||
| public double getValue(double quantile) { | ||
| if (quantile < 0.0 || quantile > 1.0 || Double.isNaN(quantile)) { | ||
| throw new IllegalArgumentException(quantile + " is not in [0..1]"); | ||
| } | ||
|
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| if (reservoir.length == 0) { | ||
| return 0.0; | ||
| } | ||
|
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| final double pos = quantile * (reservoir.length + 1); | ||
| final int index = (int) pos; | ||
|
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| if (index < 1) { | ||
| return reservoir[0]; | ||
| } | ||
|
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| if (index >= reservoir.length) { | ||
| return reservoir[reservoir.length - 1]; | ||
| } | ||
|
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| final double lower = reservoir[index - 1]; | ||
| final double upper = reservoir[index]; | ||
| return lower + (pos - Math.floor(pos)) * (upper - lower); | ||
| } | ||
|
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| /** | ||
| * Returns the standard deviation of the values. | ||
| * | ||
| * @return the standard deviation value | ||
| */ | ||
| public double getStdDev() { | ||
| if (reservoir.length <= 1) { | ||
| return 0; | ||
| } | ||
|
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| final double mean = getMean(); | ||
| double sum = 0; | ||
| for (long value : reservoir) { | ||
| final double diff = value - mean; | ||
| sum += diff * diff; | ||
| } | ||
|
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| final double variance = sum / (reservoir.length - 1); | ||
| return Math.sqrt(variance); | ||
| } | ||
| } |
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