org.glowroot.shaded.HdrHistogram.Histogram Maven / Gradle / Ivy
/**
* Written by Gil Tene of Azul Systems, and released to the public domain,
* as explained at http://creativecommons.org/publicdomain/zero/1.0/
*
* @author Gil Tene
*/
package org.glowroot.shaded.HdrHistogram;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.nio.ByteBuffer;
import java.nio.LongBuffer;
import java.util.Arrays;
import java.util.zip.DataFormatException;
/**
* A High Dynamic Range (HDR) Histogram
*
* {@link Histogram} supports the recording and analyzing sampled data value counts across a configurable integer value
* range with configurable value precision within the range. Value precision is expressed as the number of significant
* digits in the value recording, and provides control over value quantization behavior across the value range and the
* subsequent value resolution at any given level.
*
* For example, a Histogram could be configured to track the counts of observed integer values between 0 and
* 3,600,000,000 while maintaining a value precision of 3 significant digits across that range. Value quantization
* within the range will thus be no larger than 1/1,000th (or 0.1%) of any value. This example Histogram could
* be used to track and analyze the counts of observed response times ranging between 1 microsecond and 1 hour
* in magnitude, while maintaining a value resolution of 1 microsecond up to 1 millisecond, a resolution of
* 1 millisecond (or better) up to one second, and a resolution of 1 second (or better) up to 1,000 seconds. At its
* maximum tracked value (1 hour), it would still maintain a resolution of 3.6 seconds (or better).
*
* Histogram tracks value counts in long fields. Smaller field types are available in the
* {@link IntCountsHistogram} and {@link ShortCountsHistogram} implementations of
* {@link org.glowroot.shaded.HdrHistogram.AbstractHistogram}.
*
* Auto-resizing: When constructed with no specified value range range (or when auto-resize is turned on with {@link
* Histogram#setAutoResize}) a {@link Histogram} will auto-resize its dynamic range to include recorded values as
* they are encountered. Note that recording calls that cause auto-resizing may take longer to execute, as resizing
* incurs allocation and copying of internal data structures.
*
* See package description for {@link org.glowroot.shaded.HdrHistogram} for details.
*/
public class Histogram extends AbstractHistogram {
long totalCount;
long[] counts;
int normalizingIndexOffset;
@Override
long getCountAtIndex(final int index) {
return counts[normalizeIndex(index, normalizingIndexOffset, countsArrayLength)];
}
@Override
long getCountAtNormalizedIndex(final int index) {
return counts[index];
}
@Override
void incrementCountAtIndex(final int index) {
counts[normalizeIndex(index, normalizingIndexOffset, countsArrayLength)]++;
}
@Override
void addToCountAtIndex(final int index, final long value) {
counts[normalizeIndex(index, normalizingIndexOffset, countsArrayLength)] += value;
}
@Override
void setCountAtIndex(int index, long value) {
counts[normalizeIndex(index, normalizingIndexOffset, countsArrayLength)] = value;
}
@Override
void setCountAtNormalizedIndex(int index, long value) {
counts[index] = value;
}
@Override
int getNormalizingIndexOffset() {
return normalizingIndexOffset;
}
@Override
void setNormalizingIndexOffset(int normalizingIndexOffset) {
this.normalizingIndexOffset = normalizingIndexOffset;
}
@Override
void shiftNormalizingIndexByOffset(int offsetToAdd, boolean lowestHalfBucketPopulated) {
nonConcurrentNormalizingIndexShift(offsetToAdd, lowestHalfBucketPopulated);
}
@Override
void clearCounts() {
java.util.Arrays.fill(counts, 0);
totalCount = 0;
}
@Override
public Histogram copy() {
Histogram copy = new Histogram(this);
copy.add(this);
return copy;
}
@Override
public Histogram copyCorrectedForCoordinatedOmission(final long expectedIntervalBetweenValueSamples) {
Histogram copy = new Histogram(this);
copy.addWhileCorrectingForCoordinatedOmission(this, expectedIntervalBetweenValueSamples);
return copy;
}
@Override
public long getTotalCount() {
return totalCount;
}
@Override
void setTotalCount(final long totalCount) {
this.totalCount = totalCount;
}
@Override
void incrementTotalCount() {
totalCount++;
}
@Override
void addToTotalCount(final long value) {
totalCount += value;
}
@Override
int _getEstimatedFootprintInBytes() {
return (512 + (8 * counts.length));
}
@Override
void resize(long newHighestTrackableValue) {
int oldNormalizedZeroIndex = normalizeIndex(0, normalizingIndexOffset, countsArrayLength);
establishSize(newHighestTrackableValue);
int countsDelta = countsArrayLength - counts.length;
counts = Arrays.copyOf(counts, countsArrayLength);
if (oldNormalizedZeroIndex != 0) {
// We need to shift the stuff from the zero index and up to the end of the array:
int newNormalizedZeroIndex = oldNormalizedZeroIndex + countsDelta;
int lengthToCopy = (countsArrayLength - countsDelta) - oldNormalizedZeroIndex;
System.arraycopy(counts, oldNormalizedZeroIndex, counts, newNormalizedZeroIndex, lengthToCopy);
}
}
/**
* Construct an auto-resizing histogram with a lowest discernible value of 1 and an auto-adjusting
* highestTrackableValue. Can auto-resize up to track values up to (Long.MAX_VALUE / 2).
*
* @param numberOfSignificantValueDigits Specifies the precision to use. This is the number of significant
* decimal digits to which the histogram will maintain value resolution
* and separation. Must be a non-negative integer between 0 and 5.
*/
public Histogram(final int numberOfSignificantValueDigits) {
this(1, 2, numberOfSignificantValueDigits);
setAutoResize(true);
}
/**
* Construct a Histogram given the Highest value to be tracked and a number of significant decimal digits. The
* histogram will be constructed to implicitly track (distinguish from 0) values as low as 1.
*
* @param highestTrackableValue The highest value to be tracked by the histogram. Must be a positive
* integer that is {@literal >=} 2.
* @param numberOfSignificantValueDigits Specifies the precision to use. This is the number of significant
* decimal digits to which the histogram will maintain value resolution
* and separation. Must be a non-negative integer between 0 and 5.
*/
public Histogram(final long highestTrackableValue, final int numberOfSignificantValueDigits) {
this(1, highestTrackableValue, numberOfSignificantValueDigits);
}
/**
* Construct a Histogram given the Lowest and Highest values to be tracked and a number of significant
* decimal digits. Providing a lowestDiscernibleValue is useful is situations where the units used
* for the histogram's values are much smaller that the minimal accuracy required. E.g. when tracking
* time values stated in nanosecond units, where the minimal accuracy required is a microsecond, the
* proper value for lowestDiscernibleValue would be 1000.
*
* @param lowestDiscernibleValue The lowest value that can be discerned (distinguished from 0) by the
* histogram. Must be a positive integer that is {@literal >=} 1. May be
* internally rounded down to nearest power of 2.
* @param highestTrackableValue The highest value to be tracked by the histogram. Must be a positive
* integer that is {@literal >=} (2 * lowestDiscernibleValue).
* @param numberOfSignificantValueDigits Specifies the precision to use. This is the number of significant
* decimal digits to which the histogram will maintain value resolution
* and separation. Must be a non-negative integer between 0 and 5.
*/
public Histogram(final long lowestDiscernibleValue, final long highestTrackableValue,
final int numberOfSignificantValueDigits) {
this(lowestDiscernibleValue, highestTrackableValue, numberOfSignificantValueDigits, true);
}
/**
* Construct a histogram with the same range settings as a given source histogram,
* duplicating the source's start/end timestamps (but NOT its contents)
* @param source The source histogram to duplicate
*/
public Histogram(final AbstractHistogram source) {
this(source, true);
}
Histogram(final AbstractHistogram source, boolean allocateCountsArray) {
super(source);
if (allocateCountsArray) {
counts = new long[countsArrayLength];
}
wordSizeInBytes = 8;
}
Histogram(final long lowestDiscernibleValue, final long highestTrackableValue,
final int numberOfSignificantValueDigits, boolean allocateCountsArray) {
super(lowestDiscernibleValue, highestTrackableValue, numberOfSignificantValueDigits);
if (allocateCountsArray) {
counts = new long[countsArrayLength];
}
wordSizeInBytes = 8;
}
/**
* Construct a new histogram by decoding it from a ByteBuffer.
* @param buffer The buffer to decode from
* @param minBarForHighestTrackableValue Force highestTrackableValue to be set at least this high
* @return The newly constructed histogram
*/
public static Histogram decodeFromByteBuffer(final ByteBuffer buffer,
final long minBarForHighestTrackableValue) {
return (Histogram) decodeFromByteBuffer(buffer, Histogram.class, minBarForHighestTrackableValue);
}
/**
* Construct a new histogram by decoding it from a compressed form in a ByteBuffer.
* @param buffer The buffer to decode from
* @param minBarForHighestTrackableValue Force highestTrackableValue to be set at least this high
* @return The newly constructed histogram
* @throws DataFormatException on error parsing/decompressing the buffer
*/
public static Histogram decodeFromCompressedByteBuffer(final ByteBuffer buffer,
final long minBarForHighestTrackableValue) throws DataFormatException {
return (Histogram) decodeFromCompressedByteBuffer(buffer, Histogram.class,
minBarForHighestTrackableValue);
}
private void readObject(final ObjectInputStream o)
throws IOException, ClassNotFoundException {
o.defaultReadObject();
}
@Override
synchronized void fillCountsArrayFromBuffer(final ByteBuffer buffer, final int length) {
buffer.asLongBuffer().get(counts, 0, length);
}
// We try to cache the LongBuffer used in output cases, as repeated
// output form the same histogram using the same buffer is likely:
private LongBuffer cachedDstLongBuffer = null;
private ByteBuffer cachedDstByteBuffer = null;
private int cachedDstByteBufferPosition = 0;
@Override
synchronized void fillBufferFromCountsArray(final ByteBuffer buffer, final int length) {
if ((cachedDstLongBuffer == null) ||
(buffer != cachedDstByteBuffer) ||
(buffer.position() != cachedDstByteBufferPosition)) {
cachedDstByteBuffer = buffer;
cachedDstByteBufferPosition = buffer.position();
cachedDstLongBuffer = buffer.asLongBuffer();
}
cachedDstLongBuffer.rewind();
int zeroIndex = normalizeIndex(0, getNormalizingIndexOffset(), countsArrayLength);
int lengthFromZeroIndexToEnd = Math.min(length, (countsArrayLength - zeroIndex));
int remainingLengthFromNormalizedZeroIndex = length - lengthFromZeroIndexToEnd;
cachedDstLongBuffer.put(counts, zeroIndex, lengthFromZeroIndexToEnd);
cachedDstLongBuffer.put(counts, 0, remainingLengthFromNormalizedZeroIndex);
}
}