org.apache.pig.data

Class DistinctDataBag

java.lang.Object

org.apache.pig.data.DefaultAbstractBag

org.apache.pig.data.DistinctDataBag

All Implemented Interfaces:

Serializable, Comparable, Iterable<Tuple>, org.apache.hadoop.io.Writable, org.apache.hadoop.io.WritableComparable, DataBag, Spillable

public class DistinctDataBag
extends DefaultAbstractBag

An unordered collection of Tuples with no multiples. Data is stored without duplicates as it comes in. When it is time to spill, that data is sorted and written to disk. It must also be sorted upon the first read, otherwise if a spill happened after that the iterators would have no way to find their place in the new file. The data is stored in a HashSet. When it is time to sort it is placed in an ArrayList and then sorted. Dispite all these machinations, this was found to be faster than storing it in a TreeSet.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.pig.data.DefaultAbstractBag

DefaultAbstractBag.BagDelimiterTuple, DefaultAbstractBag.EndBag, DefaultAbstractBag.StartBag

Field Summary

Fields inherited from class org.apache.pig.data.DefaultAbstractBag

endBag, MAX_SPILL_FILES, mContents, mSize, mSpillFiles, startBag

Constructor Summary

Constructors

Constructor and Description
DistinctDataBag()

Method Summary

Methods

Modifier and Type	Method and Description
void	add(Tuple t) Add a tuple to the bag.
boolean	isDistinct() Find out if the bag is distinct.
boolean	isSorted() Find out if the bag is sorted.
Iterator<Tuple>	iterator() Get an iterator to the bag.
long	size() Get the number of elements in the bag, both in memory and on disk.
long	spill() Instructs an object to spill whatever it can to disk and release references to any data structures it spills.

Methods inherited from class org.apache.pig.data.DefaultAbstractBag

addAll, addAll, addAll, clear, compareTo, equals, getMemorySize, getSpillFile, hashCode, incSpillCount, incSpillCount, markSpillableIfNecessary, markStale, readFields, reportProgress, sampleContents, toString, warn, write

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

DistinctDataBag

public DistinctDataBag()

Method Detail

isSorted

public boolean isSorted()

Description copied from interface: DataBag

Find out if the bag is sorted.

Returns:

true if this is a sorted data bag, false otherwise.

isDistinct

public boolean isDistinct()

Description copied from interface: DataBag

Find out if the bag is distinct.

Returns:

true if the bag is a distinct bag, false otherwise.

size

public long size()

Description copied from class: DefaultAbstractBag

Get the number of elements in the bag, both in memory and on disk.

Specified by:

size in interface DataBag

Overrides:

size in class DefaultAbstractBag

Returns:

number of elements in the bag

iterator

public Iterator<Tuple> iterator()

Description copied from interface: DataBag

Get an iterator to the bag. For default and distinct bags, no particular order is guaranteed. For sorted bags the order is guaranteed to be sorted according to the provided comparator.

Returns:

tuple iterator

add

public void add(Tuple t)

Description copied from class: DefaultAbstractBag

Add a tuple to the bag.

Specified by:

add in interface DataBag

Overrides:

add in class DefaultAbstractBag

Parameters:

t - tuple to add.

spill

public long spill()

Description copied from interface: Spillable

Instructs an object to spill whatever it can to disk and release references to any data structures it spills.

Returns:

number of objects spilled.