Package org.apache.datasketches.hll

Class Union

java.lang.Object
org.apache.datasketches.hll.Union
public class Union extends Object
This performs union operations for all HllSketches. This union operator can be configured to be on or off heap. The source sketch given to this union using the update(HllSketch) can be configured with any precision value lgConfigK (from 4 to 21), any TgtHllType (HLL_4, HLL_6, HLL_8), and either on or off-heap; and it can be in either of the sparse modes (LIST or SET), or the dense mode (HLL).

Although the API for this union operator parallels many of the methods of the HllSketch, the behavior of the union operator has some fundamental differences.

First, this union operator is configured with a lgMaxK instead of the normal lgConfigK. Generally, this union operator will inherit the lowest lgConfigK less than lgMaxK that it has seen. However, the lgConfigK of incoming sketches that are still in sparse are ignored. The lgMaxK provides the user the ability to specify the largest maximum size for the union operation.

Second, the user cannot specify the TgtHllType as an input parameter to the union. Instead, it is specified for the sketch returned with getResult(TgtHllType).

The following graph illustrates the HLL Merge speed.

HLL LgK12 Union Speed

This graph illustrates the relative merging speed of the HLL 4,6,8 Java HLL sketches compared to the DataSketches C++ implementations of the same sketches. With this particular test (merging 32 relative large sketches together), the Java HLL 8 is the fastest and the Java HLL 4 the slowest, with a mixed cluster in the middle. Union / Merging speed is somewhat difficult to measure as the performance is very dependent on the mix of sketch sizes (and types) you are merging. So your mileage will vary!

For a complete example of using the Union operator see Union Example.

Author:
Lee Rhodes, Kevin Lang

  • Constructor Summary

    Constructors
    Constructor
    Description
    Union()
    Construct this Union operator with the default maximum log-base-2 of K.
    Union(int lgMaxK)
    Construct this Union operator with a given maximum log-base-2 of K.
    Union(int lgMaxK, org.apache.datasketches.memory.WritableMemory dstWmem)
    Construct this Union operator with a given maximum log-base-2 of K and the given WritableMemory as the destination for this Union.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    getCompactSerializationBytes()
    Gets the size in bytes of the current sketch when serialized using toCompactByteArray().
    double
    getCompositeEstimate()
    This is less accurate than the getEstimate() method and is automatically used when the sketch has gone through union operations where the more accurate HIP estimator cannot be used.
    double
    getEstimate()
    Return the cardinality estimate
    int
    getLgConfigK()
    Gets the effective lgConfigK for the union operator, which may be less than lgMaxK.
    double
    getLowerBound(int numStdDev)
    Gets the approximate lower error bound given the specified number of Standard Deviations.
    static int
    getMaxSerializationBytes(int lgK)
    Returns the maximum size in bytes that this union operator can grow to given a lgK.
    static double
    getRelErr(boolean upperBound, boolean oooFlag, int lgConfigK, int numStdDev)
    Gets the current (approximate) Relative Error (RE) asymptotic values given several parameters.
    HllSketch
    getResult()
    Return the result of this union operator as an HLL_4 sketch.
    HllSketch
    getResult(TgtHllType tgtHllType)
    Return the result of this union operator with the specified TgtHllType
    static final int
    getSerializationVersion()
    Returns the current serialization version.
    static final int
    getSerializationVersion(org.apache.datasketches.memory.Memory mem)
    Returns the current serialization version of the given Memory.
    TgtHllType
    getTgtHllType()
    Gets the TgtHllType
    int
    getUpdatableSerializationBytes()
    Gets the size in bytes of the current sketch when serialized using toUpdatableByteArray().
    double
    getUpperBound(int numStdDev)
    Gets the approximate upper error bound given the specified number of Standard Deviations.
    static final Union
    heapify(byte[] byteArray)
    Construct a union operator populated with the given byte array image of an HllSketch.
    static final Union
    heapify(org.apache.datasketches.memory.Memory mem)
    Construct a union operator populated with the given Memory image of an HllSketch.
    boolean
    isCompact()
    Returns true if the backing memory of this sketch is in compact form.
    boolean
    isEmpty()
    Returns true if empty
    boolean
    isEstimationMode()
    This HLL family of sketches and operators is always estimating, even for very small values.
    boolean
    isMemory()
    Returns true if this sketch was created using Memory.
    boolean
    isOffHeap()
    Returns true if the backing memory for this sketch is off-heap.
    boolean
    isSameResource(org.apache.datasketches.memory.Memory mem)
    Returns true if the given Memory refers to the same underlying resource as this sketch.
    void
    reset()
    Resets to empty and retains the current lgK, but does not change the configured value of lgMaxK.
    byte[]
    toCompactByteArray()
    Gets the serialization of this union operator as a byte array in compact form, which is designed to be heapified only.
    String
    toString()
    Human readable summary as a string.
    String
    toString(boolean summary, boolean detail, boolean auxDetail)
    Human readable summary with optional detail.
    String
    toString(boolean summary, boolean hllDetail, boolean auxDetail, boolean all)
    Human readable summary with optional detail
    byte[]
    toUpdatableByteArray()
    Serializes this sketch as a byte array in an updatable form.
    void
    update(byte[] data)
    Present the given byte array as a potential unique item.
    void
    update(char[] data)
    Present the given char array as a potential unique item.
    void
    update(double datum)
    Present the given double (or float) datum as a potential unique item.
    void
    update(int[] data)
    Present the given integer array as a potential unique item.
    void
    update(long datum)
    Present the given long as a potential unique item.
    void
    update(long[] data)
    Present the given long array as a potential unique item.
    void
    update(String datum)
    Present the given String as a potential unique item.
    void
    update(ByteBuffer data)
    Present the given byte buffer as a potential unique item.
    void
    update(HllSketch sketch)
    Update this union operator with the given sketch.
    static final Union
    writableWrap(org.apache.datasketches.memory.WritableMemory srcWmem)
    Wraps the given WritableMemory, which must be a image of a valid updatable HLL_8 sketch, and may have data.

    Methods inherited from class java.lang.Object

    equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Constructor Details

    • Union

      public Union()
      Construct this Union operator with the default maximum log-base-2 of K.

    • Union

      public Union(int lgMaxK)
      Construct this Union operator with a given maximum log-base-2 of K.
      Parameters:
      lgMaxK - the desired maximum log-base-2 of K. This value must be between 4 and 21 inclusively.

    • Union

      public Union(int lgMaxK, org.apache.datasketches.memory.WritableMemory dstWmem)
      Construct this Union operator with a given maximum log-base-2 of K and the given WritableMemory as the destination for this Union. This WritableMemory is usually configured for off-heap memory. What remains on the java heap is a thin wrapper object that reads and writes to the given WritableMemory.

      The given dstMem is checked for the required capacity as determined by HllSketch.getMaxUpdatableSerializationBytes(int, TgtHllType).

      Parameters:
      lgMaxK - the desired maximum log-base-2 of K. This value must be between 4 and 21 inclusively.
      dstWmem - the destination writable memory for the sketch.

  • Method Details

    • heapify

      public static final Union heapify(byte[] byteArray)
      Construct a union operator populated with the given byte array image of an HllSketch.
      Parameters:
      byteArray - the given byte array
      Returns:
      a union operator populated with the given byte array image of an HllSketch.

    • heapify

      public static final Union heapify(org.apache.datasketches.memory.Memory mem)
      Construct a union operator populated with the given Memory image of an HllSketch.
      Parameters:
      mem - the given Memory
      Returns:
      a union operator populated with the given Memory image of an HllSketch.

    • writableWrap

      public static final Union writableWrap(org.apache.datasketches.memory.WritableMemory srcWmem)
      Wraps the given WritableMemory, which must be a image of a valid updatable HLL_8 sketch, and may have data. What remains on the java heap is a thin wrapper object that reads and writes to the given WritableMemory, which, depending on how the user configures the WritableMemory, may actually reside on the Java heap or off-heap.

      The given dstMem is checked for the required capacity as determined by HllSketch.getMaxUpdatableSerializationBytes(int, TgtHllType), and for the correct type.

      Parameters:
      srcWmem - an writable image of a valid sketch with data.
      Returns:
      a Union operator where the sketch data is in the given dstMem.

    • getCompositeEstimate

      public double getCompositeEstimate()
      This is less accurate than the getEstimate() method and is automatically used when the sketch has gone through union operations where the more accurate HIP estimator cannot be used. This is made public only for error characterization software that exists in separate packages and is not intended for normal use.
      Returns:
      the composite estimate

    • getCompactSerializationBytes

      public int getCompactSerializationBytes()
      Gets the size in bytes of the current sketch when serialized using toCompactByteArray().
      Returns:
      the size in bytes of the current sketch when serialized using toCompactByteArray().

    • getEstimate

      public double getEstimate()
      Return the cardinality estimate
      Returns:
      the cardinality estimate

    • getLgConfigK

      public int getLgConfigK()
      Gets the effective lgConfigK for the union operator, which may be less than lgMaxK.
      Returns:
      the lgConfigK.

    • getLowerBound

      public double getLowerBound(int numStdDev)
      Gets the approximate lower error bound given the specified number of Standard Deviations.
      Parameters:
      numStdDev - This must be an integer between 1 and 3, inclusive. See Number of Standard Deviations
      Returns:
      the lower bound.

    • getMaxSerializationBytes

      public static int getMaxSerializationBytes(int lgK)
      Returns the maximum size in bytes that this union operator can grow to given a lgK.
      Parameters:
      lgK - The maximum Log2 of K for this union operator. This value must be between 4 and 21 inclusively.
      Returns:
      the maximum size in bytes that this union operator can grow to.

    • getResult

      public HllSketch getResult()
      Return the result of this union operator as an HLL_4 sketch.
      Returns:
      the result of this union operator as an HLL_4 sketch.

    • getResult

      public HllSketch getResult(TgtHllType tgtHllType)
      Return the result of this union operator with the specified TgtHllType
      Parameters:
      tgtHllType - the TgtHllType enum
      Returns:
      the result of this union operator with the specified TgtHllType

    • getTgtHllType

      public TgtHllType getTgtHllType()
      Gets the TgtHllType
      Returns:
      the TgtHllType enum value

    • getUpdatableSerializationBytes

      public int getUpdatableSerializationBytes()
      Gets the size in bytes of the current sketch when serialized using toUpdatableByteArray().
      Returns:
      the size in bytes of the current sketch when serialized using toUpdatableByteArray().

    • getUpperBound

      public double getUpperBound(int numStdDev)
      Gets the approximate upper error bound given the specified number of Standard Deviations.
      Parameters:
      numStdDev - This must be an integer between 1 and 3, inclusive. Number of Standard Deviations
      Returns:
      the upper bound.

    • isCompact

      public boolean isCompact()
      Returns true if the backing memory of this sketch is in compact form.
      Returns:
      true if the backing memory of this sketch is in compact form.

    • isEmpty

      public boolean isEmpty()
      Returns true if empty
      Returns:
      true if empty

    • isMemory

      public boolean isMemory()
      Returns true if this sketch was created using Memory.
      Returns:
      true if this sketch was created using Memory.

    • isOffHeap

      public boolean isOffHeap()
      Returns true if the backing memory for this sketch is off-heap.
      Returns:
      true if the backing memory for this sketch is off-heap.

    • isSameResource

      public boolean isSameResource(org.apache.datasketches.memory.Memory mem)
      Returns true if the given Memory refers to the same underlying resource as this sketch. The capacities must be the same. If this is a region, the region offset must also be the same.

      This is only relevant for HLL_4 sketches that have been configured for off-heap using WritableMemory or Memory. For on-heap sketches or unions this will return false.

      It is rare, but possible, the the off-heap memory that has been allocated to an HLL_4 sketch may not be large enough. If this should happen, the sketch makes a request for more memory from the owner of the resource and then moves itself to this new location. This all happens transparently to the user. This method provides a means for the user to inquire of the sketch if it has, in fact, moved itself.

      Parameters:
      mem - the given Memory
      Returns:
      true if the given Memory refers to the same underlying resource as this sketch or union.

    • reset

      public void reset()
      Resets to empty and retains the current lgK, but does not change the configured value of lgMaxK.

    • toCompactByteArray

      public byte[] toCompactByteArray()
      Gets the serialization of this union operator as a byte array in compact form, which is designed to be heapified only. It is not directly updatable. For the Union operator, this is the serialization of the internal state of the union operator as a sketch.
      Returns:
      the serialization of this union operator as a byte array.

    • toUpdatableByteArray

      public byte[] toUpdatableByteArray()
      Serializes this sketch as a byte array in an updatable form. The updatable form is larger than the compact form. The use of this form is primarily in environments that support updating sketches in off-heap memory. If the sketch is constructed using HLL_8, sketch updating and union updating operations can actually occur in WritableMemory, which can be off-heap: 
      
     Union union; HllSketch sk;
     int lgK = 12;
     sk = new HllSketch(lgK, TgtHllType.HLL_8) //must be 8
     for (int i = 0; i < (2 << lgK); i++) { sk.update(i); }
     byte[] arr = sk.toUpdatableByteArray();
     WritableMemory wmem = WritableMemory.wrap(arr);
     //...
     union = Union.writableWrap(wmem); //no deserialization!
      Returns:
      this sketch as an updatable byte array.

    • toString

      public String toString(boolean summary, boolean hllDetail, boolean auxDetail, boolean all)
      Human readable summary with optional detail
      Parameters:
      summary - if true, output the sketch summary
      hllDetail - if true, output the internal data array
      auxDetail - if true, output the internal Aux array, if it exists.
      all - if true, outputs all entries including empty ones
      Returns:
      human readable string with optional detail.

    • update

      public void update(HllSketch sketch)
      Update this union operator with the given sketch.
      Parameters:
      sketch - the given sketch.

    • getSerializationVersion

      public static final int getSerializationVersion()
      Returns the current serialization version.
      Returns:
      the current serialization version.

    • getSerializationVersion

      public static final int getSerializationVersion(org.apache.datasketches.memory.Memory mem)
      Returns the current serialization version of the given Memory.
      Parameters:
      mem - the given Memory containing a serialized HllSketch image.
      Returns:
      the current serialization version.

    • getRelErr

      public static double getRelErr(boolean upperBound, boolean oooFlag, int lgConfigK, int numStdDev)
      Gets the current (approximate) Relative Error (RE) asymptotic values given several parameters. This is used primarily for testing.
      Parameters:
      upperBound - return the RE for the Upper Bound, otherwise for the Lower Bound.
      oooFlag - set true if the sketch is the result of a non qualifying union operation.
      lgConfigK - the configured value for the sketch.
      numStdDev - the given number of Standard Deviations. This must be an integer between 1 and 3, inclusive. Number of Standard Deviations
      Returns:
      the current (approximate) RelativeError

    • isEstimationMode

      public boolean isEstimationMode()
      This HLL family of sketches and operators is always estimating, even for very small values.
      Returns:
      true

    • toString

      public String toString()
      Human readable summary as a string.
      Overrides:
      toString in class Object
      Returns:
      Human readable summary as a string.

    • toString

      public String toString(boolean summary, boolean detail, boolean auxDetail)
      Human readable summary with optional detail. Does not list empty entries.
      Parameters:
      summary - if true, output the sketch summary
      detail - if true, output the internal data array
      auxDetail - if true, output the internal Aux array, if it exists.
      Returns:
      human readable string with optional detail.

    • update

      public void update(long datum)
      Present the given long as a potential unique item.
      Parameters:
      datum - The given long datum.

    • update

      public void update(double datum)
      Present the given double (or float) datum as a potential unique item. The double will be converted to a long using Double.doubleToLongBits(datum), which normalizes all NaN values to a single NaN representation. Plus and minus zero will be normalized to plus zero. The special floating-point values NaN and +/- Infinity are treated as distinct.
      Parameters:
      datum - The given double datum.

    • update

      public void update(String datum)
      Present the given String as a potential unique item. The string is converted to a byte array using UTF8 encoding. If the string is null or empty no update attempt is made and the method returns.

      Note: About 2X faster performance can be obtained by first converting the String to a char[] and updating the sketch with that. This bypasses the complexity of the Java UTF_8 encoding. This, of course, will not produce the same internal hash values as updating directly with a String. So be consistent! Unioning two sketches, one fed with strings and the other fed with char[] will be meaningless.

      Parameters:
      datum - The given String.

    • update

      public void update(ByteBuffer data)
      Present the given byte buffer as a potential unique item. Bytes are read from the current position of the buffer until its limit. If the byte buffer is null or has no bytes remaining, no update attempt is made and the method returns.

      This method will not modify the position, mark, limit, or byte order of the buffer.

      Little-endian order is preferred, but not required. This method may perform better if the provided byte buffer is in little-endian order.

      Parameters:
      data - The given byte buffer.

    • update

      public void update(byte[] data)
      Present the given byte array as a potential unique item. If the byte array is null or empty no update attempt is made and the method returns.
      Parameters:
      data - The given byte array.

    • update

      public void update(char[] data)
      Present the given char array as a potential unique item. If the char array is null or empty no update attempt is made and the method returns.

      Note: this will not produce the same output hash values as the update(String) method but will be a little faster as it avoids the complexity of the UTF8 encoding.

      Parameters:
      data - The given char array.

    • update

      public void update(int[] data)
      Present the given integer array as a potential unique item. If the integer array is null or empty no update attempt is made and the method returns.
      Parameters:
      data - The given int array.

    • update

      public void update(long[] data)
      Present the given long array as a potential unique item. If the long array is null or empty no update attempt is made and the method returns.
      Parameters:
      data - The given long array.