Package org.apache.hadoop.io

Class BloomMapFile.Reader

java.lang.Object

org.apache.hadoop.io.MapFile.Reader

org.apache.hadoop.io.BloomMapFile.Reader

All Implemented Interfaces:

Closeable, AutoCloseable

Enclosing class:

BloomMapFile

public static class BloomMapFile.Reader
extends MapFile.Reader

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.io.MapFile.Reader

MapFile.Reader.Option

Constructor Summary

Constructors

Constructor	Description
Reader(FileSystem fs, String dirName, Configuration conf)	Deprecated.
Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf)	Deprecated.
Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf, boolean open)	Deprecated.
Reader(Path dir, Configuration conf, SequenceFile.Reader.Option... options)

Method Summary

Modifier and Type	Method	Description
Writable	get(WritableComparable key, Writable val)	Fast version of the MapFile.Reader.get(WritableComparable, Writable) method.
Filter	getBloomFilter()	Retrieve the Bloom filter used by this instance of the Reader.
boolean	probablyHasKey(WritableComparable key)	Checks if this MapFile has the indicated key.

Methods inherited from class org.apache.hadoop.io.MapFile.Reader

close, comparator, createDataFileReader, finalKey, getClosest, getClosest, getKeyClass, getValueClass, midKey, next, open, reset, seek

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Reader

public Reader(Path dir,
 Configuration conf,
 SequenceFile.Reader.Option... options)
       throws IOException

Throws:

IOException

Reader

@Deprecated
public Reader(FileSystem fs,
 String dirName,
 Configuration conf)
       throws IOException

Deprecated.

Throws:

IOException

Reader

@Deprecated
public Reader(FileSystem fs,
 String dirName,
 WritableComparator comparator,
 Configuration conf,
 boolean open)
       throws IOException

Deprecated.

Throws:

IOException

Reader

@Deprecated
public Reader(FileSystem fs,
 String dirName,
 WritableComparator comparator,
 Configuration conf)
       throws IOException

Deprecated.

Throws:

IOException

Method Details

probablyHasKey

public boolean probablyHasKey(WritableComparable key)
                       throws IOException

Checks if this MapFile has the indicated key. The membership test is performed using a Bloom filter, so the result has always non-zero probability of false positives.

Parameters:

key - key to check

Returns:

false iff key doesn't exist, true if key probably exists.

Throws:

IOException - raised on errors performing I/O.

get

public Writable get(WritableComparable key,
 Writable val)
             throws IOException

Fast version of the MapFile.Reader.get(WritableComparable, Writable) method. First it checks the Bloom filter for the existence of the key, and only if present it performs the real get operation. This yields significant performance improvements for get operations on sparsely populated files.

Overrides:

get in class MapFile.Reader

Parameters:

key - key.

val - val.

Returns:

Writable if such a pair exists true,not false.

Throws:

IOException - raised on errors performing I/O.

getBloomFilter

public Filter getBloomFilter()

Retrieve the Bloom filter used by this instance of the Reader.

Returns:

a Bloom filter (see Filter)