org.apache.accumulo.core.iterators
Class Combiner

java.lang.Object
  extended by org.apache.accumulo.core.iterators.WrappingIterator
      extended by org.apache.accumulo.core.iterators.Combiner
All Implemented Interfaces:
OptionDescriber, SortedKeyValueIterator<Key,Value>
Direct Known Subclasses:
TypedValueCombiner

public abstract class Combiner
extends WrappingIterator
implements OptionDescriber

A SortedKeyValueIterator that combines the Values for different versions (timestamps) of a Key into a single Value. Combiner will replace one or more versions of a Key and their Values with the most recent Key and a Value which is the result of the reduce method. Subclasses must implement a reduce method: public Value reduce(Key key, Iterator<Value> iter). This reduce method will be passed the most recent Key and an iterator over the Values for all non-deleted versions of that Key. A combiner will not combine keys that differ by more than the timestamp.


Nested Class Summary
static class Combiner.ValueIterator
          A Java Iterator that iterates over the Values for a given Key from a source SortedKeyValueIterator.
 
Nested classes/interfaces inherited from interface org.apache.accumulo.core.iterators.OptionDescriber
OptionDescriber.IteratorOptions
 
Field Summary
protected static String ALL_OPTION
           
protected static String COLUMNS_OPTION
           
 
Constructor Summary
Combiner()
           
 
Method Summary
 SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
          Creates a deep copy of this iterator as though seek had not yet been called.
 OptionDescriber.IteratorOptions describeOptions()
          Gets an iterator options object that contains information needed to configure this iterator.
 Key getTopKey()
          Returns top key.
 Value getTopValue()
          Returns top value.
 boolean hasTop()
          Returns true if the iterator has more elements.
 void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env)
          Initializes the iterator.
 void next()
          Advances to the next K,V pair.
abstract  Value reduce(Key key, Iterator<Value> iter)
          Reduces a list of Values into a single Value.
 void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive)
          Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns.
static void setColumns(IteratorSetting is, List<IteratorSetting.Column> columns)
          A convenience method to set which columns a combiner should be applied to.
static void setCombineAllColumns(IteratorSetting is, boolean combineAllColumns)
          A convenience method to set the "all columns" option on a Combiner.
 boolean validateOptions(Map<String,String> options)
          Check to see if an options map contains all options required by an iterator and that the option values are in the expected formats.
 
Methods inherited from class org.apache.accumulo.core.iterators.WrappingIterator
getSource, setSource
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

COLUMNS_OPTION

protected static final String COLUMNS_OPTION
See Also:
Constant Field Values

ALL_OPTION

protected static final String ALL_OPTION
See Also:
Constant Field Values
Constructor Detail

Combiner

public Combiner()
Method Detail

getTopKey

public Key getTopKey()
Description copied from interface: SortedKeyValueIterator
Returns top key. Can be called 0 or more times without affecting behavior of next() or hasTop(). Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.

Specified by:
getTopKey in interface SortedKeyValueIterator<Key,Value>
Overrides:
getTopKey in class WrappingIterator
Returns:
K

getTopValue

public Value getTopValue()
Description copied from interface: SortedKeyValueIterator
Returns top value. Can be called 0 or more times without affecting behavior of next() or hasTop().

Specified by:
getTopValue in interface SortedKeyValueIterator<Key,Value>
Overrides:
getTopValue in class WrappingIterator
Returns:
V

hasTop

public boolean hasTop()
Description copied from interface: SortedKeyValueIterator
Returns true if the iterator has more elements.

Specified by:
hasTop in interface SortedKeyValueIterator<Key,Value>
Overrides:
hasTop in class WrappingIterator
Returns:
true if the iterator has more elements.

next

public void next()
          throws IOException
Description copied from interface: SortedKeyValueIterator
Advances to the next K,V pair. Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.

Specified by:
next in interface SortedKeyValueIterator<Key,Value>
Overrides:
next in class WrappingIterator
Throws:
IOException - if an I/O error occurs.

seek

public void seek(Range range,
                 Collection<ByteSequence> columnFamilies,
                 boolean inclusive)
          throws IOException
Description copied from interface: SortedKeyValueIterator
Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns. An iterator does not have to stop at the end of the range. The whole range is provided so that iterators can make optimizations. Seek may be called multiple times with different parameters after SortedKeyValueIterator.init(org.apache.accumulo.core.iterators.SortedKeyValueIterator, java.util.Map, org.apache.accumulo.core.iterators.IteratorEnvironment) is called. Iterators that examine groups of adjacent key/value pairs (e.g. rows) to determine their top key and value should be sure that they properly handle a seek to a key in the middle of such a group (e.g. the middle of a row). Even if the client always seeks to a range containing an entire group (a,c), the tablet server could send back a batch of entries corresponding to (a,b], then reseek the iterator to range (b,c) when the scan is continued. columnFamilies is used, at the lowest level, to determine which data blocks inside of an RFile need to be opened for this iterator. This set of data blocks is also the set of locality groups defined for the given table. If no columnFamilies are provided, the data blocks for all locality groups inside of the correct RFile will be opened and seeked in an attempt to find the correct start key, regardless of the startKey in the range. In an Accumulo instance in which multiple locality groups exist for a table, it is important to ensure that columnFamilies is properly set to the minimum required column families to ensure that data from separate locality groups is not inadvertently read.

Specified by:
seek in interface SortedKeyValueIterator<Key,Value>
Overrides:
seek in class WrappingIterator
Parameters:
range - Range of keys to iterate over.
columnFamilies - Collection of column families to include or exclude.
inclusive - boolean that indicates whether to include (true) or exclude (false) column families.
Throws:
IOException - if an I/O error occurs.

reduce

public abstract Value reduce(Key key,
                             Iterator<Value> iter)
Reduces a list of Values into a single Value.

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 WrappingIterator
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.
Throws:
IOException - unused.

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.

Specified by:
deepCopy in interface SortedKeyValueIterator<Key,Value>
Overrides:
deepCopy in class WrappingIterator
Parameters:
env - IteratorEnvironment environment in which iterator is being run.
Returns:
SortedKeyValueIterator a copy of this iterator (with the same source and settings).

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
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
Parameters:
options - a map of option names to option values
Returns:
true if options are valid, false otherwise (IllegalArgumentException preferred)

setColumns

public static void setColumns(IteratorSetting is,
                              List<IteratorSetting.Column> columns)
A convenience method to set which columns a combiner should be applied to.

Parameters:
is - iterator settings object to configure
columns - a list of columns to encode as the value for the combiner column configuration

setCombineAllColumns

public static void setCombineAllColumns(IteratorSetting is,
                                        boolean combineAllColumns)
A convenience method to set the "all columns" option on a Combiner.

Parameters:
is - iterator settings object to configure
combineAllColumns - if true, the columns option is ignored and the Combiner will be applied to all columns


Copyright © 2013 Apache Accumulo Project. All Rights Reserved.