Package org.HdrHistogram

Class PackedHistogram

  • All Implemented Interfaces:
    Serializable, ValueRecorder
    public class PackedHistogram
extends Histogram

    A High Dynamic Range (HDR) Histogram that uses a packed internal representation

    PackedHistogram 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.

    PackedHistogram tracks value counts in a packed internal representation optimized for typical histogram recoded values are sparse in the value range and tend to be incremented in small unit counts. This packed representation tends to require significantly smaller amounts of storage when compared to unpacked representations, but can incur additional recording cost due to resizing and repacking operations that may occur as previously unrecorded values are encountered.

    For example, a PackedHistogram could be configured to track the counts of observed integer values between 0 and 3,600,000,000,000 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 nanosecond 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).

    Auto-resizing: When constructed with no specified value range range (or when auto-resize is turned on with AbstractHistogram.setAutoResize(boolean)) a PackedHistogram 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 org.HdrHistogram for details.

    See Also:
    Serialized Form

    • Constructor Detail

      • PackedHistogram

        public PackedHistogram​(int numberOfSignificantValueDigits)
        Construct an auto-resizing PackedHistogram 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).
        Parameters:
        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.

      • PackedHistogram

        public PackedHistogram​(long highestTrackableValue,
                       int numberOfSignificantValueDigits)
        Construct a PackedHistogram 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.
        Parameters:
        highestTrackableValue - The highest value to be tracked by the histogram. Must be a positive integer that is >= 2.
        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.

      • PackedHistogram

        public PackedHistogram​(long lowestDiscernibleValue,
                       long highestTrackableValue,
                       int numberOfSignificantValueDigits)
        Construct a PackedHistogram 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.
        Parameters:
        lowestDiscernibleValue - The lowest value that can be tracked (distinguished from 0) by the histogram. Must be a positive integer that is >= 1. May be internally rounded down to nearest power of 2.
        highestTrackableValue - The highest value to be tracked by the histogram. Must be a positive integer that is >= (2 * lowestDiscernibleValue).
        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.

      • PackedHistogram

        public PackedHistogram​(AbstractHistogram source)
        Construct a PackedHistogram with the same range settings as a given source histogram, duplicating the source's start/end timestamps (but NOT it's contents)
        Parameters:
        source - The source histogram to duplicate

    • Method Detail

      • copy

        public PackedHistogram copy()
        Description copied from class: AbstractHistogram
        Create a copy of this histogram, complete with data and everything.
        Overrides:
        copy in class Histogram
        Returns:
        A distinct copy of this histogram.

      • copyCorrectedForCoordinatedOmission

        public PackedHistogram copyCorrectedForCoordinatedOmission​(long expectedIntervalBetweenValueSamples)
        Description copied from class: AbstractHistogram
        Get a copy of this histogram, corrected for coordinated omission.

        To compensate for the loss of sampled values when a recorded value is larger than the expected interval between value samples, the new histogram will include an auto-generated additional series of decreasingly-smaller (down to the expectedIntervalBetweenValueSamples) value records for each count found in the current histogram that is larger than the expectedIntervalBetweenValueSamples. Note: This is a post-correction method, as opposed to the at-recording correction method provided by recordValueWithExpectedInterval. The two methods are mutually exclusive, and only one of the two should be be used on a given data set to correct for the same coordinated omission issue. by

        See notes in the description of the Histogram calls for an illustration of why this corrective behavior is important.

        Overrides:
        copyCorrectedForCoordinatedOmission in class Histogram
        Parameters:
        expectedIntervalBetweenValueSamples - If expectedIntervalBetweenValueSamples is larger than 0, add auto-generated value records as appropriate if value is larger than expectedIntervalBetweenValueSamples
        Returns:
        a copy of this histogram, corrected for coordinated omission.

      • decodeFromByteBuffer

        public static PackedHistogram decodeFromByteBuffer​(ByteBuffer buffer,
                                                   long minBarForHighestTrackableValue)
        Construct a new histogram by decoding it from a ByteBuffer.
        Parameters:
        buffer - The buffer to decode from
        minBarForHighestTrackableValue - Force highestTrackableValue to be set at least this high
        Returns:
        The newly constructed histogram

      • decodeFromCompressedByteBuffer

        public static PackedHistogram decodeFromCompressedByteBuffer​(ByteBuffer buffer,
                                                             long minBarForHighestTrackableValue)
                                                      throws DataFormatException
        Construct a new histogram by decoding it from a compressed form in a ByteBuffer.
        Parameters:
        buffer - The buffer to decode from
        minBarForHighestTrackableValue - Force highestTrackableValue to be set at least this high
        Returns:
        The newly constructed histogram
        Throws:
        DataFormatException - on error parsing/decompressing the buffer