Package org.apache.accumulo.core.iterators

Class TypedValueCombiner<V>

java.lang.Object
org.apache.accumulo.core.iterators.WrappingIterator
org.apache.accumulo.core.iterators.Combiner
org.apache.accumulo.core.iterators.TypedValueCombiner<V>
All Implemented Interfaces:
OptionDescriber, SortedKeyValueIterator<Key,Value>, YieldingKeyValueIterator<Key,Value>
Direct Known Subclasses:
BigDecimalCombiner, LongCombiner, SummingArrayCombiner
public abstract class TypedValueCombiner<V> extends Combiner
A Combiner that decodes each Value to type V before reducing, then encodes the result of typedReduce back to Value. Subclasses must implement a typedReduce method: public V typedReduce(Key key, Iterator<V> iter); This typedReduce method will be passed the most recent Key and an iterator over the Values (translated to Vs) for all non-deleted versions of that Key. Subclasses may implement a switch on the "type" variable to choose an Encoder in their init method.

  • Field Details

  • Constructor Details

    • TypedValueCombiner

      public TypedValueCombiner()

  • Method Details

    • setEncoder

      protected void setEncoder(Encoder<V> encoder)
      Sets the Encoder<V> used to translate Values to V and back.

    • setEncoder

      protected void setEncoder(String encoderClass)
      Instantiates and sets the Encoder<V> used to translate Values to V and back.
      Throws:
      IllegalArgumentException - if ClassNotFoundException, InstantiationException, or IllegalAccessException occurs

    • testEncoder

      protected void testEncoder(V v)
      Tests whether v remains the same when encoded and decoded with the current encoder.
      Throws:
      IllegalStateException - if an encoder has not been set.
      IllegalArgumentException - if the test fails.

    • testEncoder

      public static <V> void testEncoder(Encoder<V> encoder, V v)
      Tests whether v remains the same when encoded and decoded with the given encoder.
      Throws:
      IllegalArgumentException - if the test fails.

    • deepCopy

      public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
      Description copied from interface: SortedKeyValueIterator
      Creates a deep copy of this iterator as though seek had not yet been called. init should be called on an iterator before deepCopy is called. init should not need to be called on the copy that is returned by deepCopy; that is, when necessary init should be called in the deepCopy method on the iterator it returns. The behavior is unspecified if init is called after deepCopy either on the original or the copy. A proper implementation would call deepCopy on the source.
      Specified by:
      deepCopy in interface SortedKeyValueIterator<Key,Value>
      Overrides:
      deepCopy in class Combiner
      Parameters:
      env - IteratorEnvironment environment in which iterator is being run, provided by Accumulo itself and is expected to be non-null.
      Returns:
      SortedKeyValueIterator a copy of this iterator (with the same source and settings).

    • reduce

      public Value reduce(Key key, Iterator<Value> iter)
      Description copied from class: Combiner
      Reduces a list of Values into a single Value.
      Specified by:
      reduce in class Combiner
      Parameters:
      key - The most recent version of the Key being reduced.
      iter - An iterator over the Values for different versions of the key.
      Returns:
      The combined Value.

    • init

      public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) throws IOException
      Description copied from interface: SortedKeyValueIterator
      Initializes the iterator. Data should not be read from the source in this method.
      Specified by:
      init in interface SortedKeyValueIterator<Key,Value>
      Overrides:
      init in class Combiner
      Parameters:
      source - SortedKeyValueIterator source to read data from.
      options - Map map of string option names to option values.
      env - IteratorEnvironment environment in which iterator is being run, provided by Accumulo itself and is expected to be non-null.
      Throws:
      IOException - unused.

    • describeOptions

      public OptionDescriber.IteratorOptions describeOptions()
      Description copied from interface: OptionDescriber
      Gets an iterator options object that contains information needed to configure this iterator. This object will be used by the accumulo shell to prompt the user to input the appropriate information.
      Specified by:
      describeOptions in interface OptionDescriber
      Overrides:
      describeOptions in class Combiner
      Returns:
      an iterator options object

    • validateOptions

      public boolean validateOptions(Map<String,String> options)
      Description copied from interface: OptionDescriber
      Check to see if an options map contains all options required by an iterator and that the option values are in the expected formats.
      Specified by:
      validateOptions in interface OptionDescriber
      Overrides:
      validateOptions in class Combiner
      Parameters:
      options - a map of option names to option values
      Returns:
      true if options are valid, false otherwise (IllegalArgumentException preferred)

    • setLossyness

      public static void setLossyness(IteratorSetting is, boolean lossy)
      A convenience method to set the "lossy" option on a TypedValueCombiner. If true, the combiner will ignore any values which fail to decode. Otherwise, the combiner will throw an error which will interrupt the action (and prevent potential data loss). False is the default behavior.
      Parameters:
      is - iterator settings object to configure
      lossy - if true the combiner will ignored values which fail to decode; otherwise error.

    • typedReduce

      public abstract V typedReduce(Key key, Iterator<V> iter)
      Reduces a list of V into a single V.
      Parameters:
      key - The most recent version of the Key being reduced.
      iter - An iterator over the V for different versions of the key.
      Returns:
      The combined V.