org.apache.accumulo.core.iterators
public abstract class Combiner extends WrappingIterator implements OptionDescriber
IteratorSetting.Column
which only specifies a column family will combine all Keys in that column family individually. Similarly, a IteratorSetting.Column
which specifies a
column family and column qualifier will combine all Keys in column family and qualifier individually. Combination is only ever performed on multiple versions
and not across column qualifiers or column visibilities.
Implementations must provide 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.
This class and its implementations do not automatically filter out unwanted columns from those being combined, thus it is generally recommended to use a
Combiner
implementation with the ScannerBase.fetchColumnFamily(Text)
or ScannerBase.fetchColumn(Text, Text)
methods.Modifier and Type | Class and Description |
---|---|
static class |
Combiner.ValueIterator
A Java Iterator that iterates over the Values for a given Key from a source SortedKeyValueIterator.
|
OptionDescriber.IteratorOptions
Modifier and Type | Field and Description |
---|---|
protected static String |
ALL_OPTION |
protected static String |
COLUMNS_OPTION |
Constructor and Description |
---|
Combiner() |
Modifier and Type | Method and Description |
---|---|
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.
|
getSource, setSource
protected static final String COLUMNS_OPTION
protected static final String ALL_OPTION
public Key getTopKey()
SortedKeyValueIterator
getTopKey
in interface SortedKeyValueIterator<Key,Value>
getTopKey
in class WrappingIterator
public Value getTopValue()
SortedKeyValueIterator
getTopValue
in interface SortedKeyValueIterator<Key,Value>
getTopValue
in class WrappingIterator
public boolean hasTop()
SortedKeyValueIterator
hasTop
in interface SortedKeyValueIterator<Key,Value>
hasTop
in class WrappingIterator
public void next() throws IOException
SortedKeyValueIterator
next
in interface SortedKeyValueIterator<Key,Value>
next
in class WrappingIterator
IOException
- if an I/O error occurs.public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive) throws IOException
SortedKeyValueIterator
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.seek
in interface SortedKeyValueIterator<Key,Value>
seek
in class WrappingIterator
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.IOException
- if an I/O error occurs.public abstract Value reduce(Key key, Iterator<Value> iter)
key
- The most recent version of the Key being reduced.iter
- An iterator over the Values for different versions of the key.public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) throws IOException
SortedKeyValueIterator
init
in interface SortedKeyValueIterator<Key,Value>
init
in class WrappingIterator
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.IOException
- unused.public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
SortedKeyValueIterator
deepCopy
in interface SortedKeyValueIterator<Key,Value>
deepCopy
in class WrappingIterator
env
- IteratorEnvironment environment in which iterator is being run.public OptionDescriber.IteratorOptions describeOptions()
OptionDescriber
describeOptions
in interface OptionDescriber
public boolean validateOptions(Map<String,String> options)
OptionDescriber
validateOptions
in interface OptionDescriber
options
- a map of option names to option valuespublic static void setColumns(IteratorSetting is, List<IteratorSetting.Column> columns)
ScannerBase.fetchColumnFamily(Text)
or ScannerBase.fetchColumn(Text,Text)
.is
- iterator settings object to configurecolumns
- a list of columns to encode as the value for the combiner column configurationpublic static void setCombineAllColumns(IteratorSetting is, boolean combineAllColumns)
is
- iterator settings object to configurecombineAllColumns
- if true, the columns option is ignored and the Combiner will be applied to all columnsCopyright © 2014 Apache Accumulo Project. All rights reserved.