org.apache.hadoop.io

类 BloomMapFile.Reader

java.lang.Object

org.apache.hadoop.io.MapFile.Reader

org.apache.hadoop.io.BloomMapFile.Reader

所有已实现的接口:

Closeable, AutoCloseable

封闭类:

BloomMapFile

public static class BloomMapFile.Reader
extends MapFile.Reader

构造器概要

构造器

构造器和说明
BloomMapFile.Reader(FileSystem fs, String dirName, Configuration conf)
BloomMapFile.Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf)
BloomMapFile.Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf, boolean open)

方法概要

方法

限定符和类型	方法和说明
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.

从类继承的方法 org.apache.hadoop.io.MapFile.Reader

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

从类继承的方法 java.lang.Object

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

构造器详细资料

BloomMapFile.Reader

public BloomMapFile.Reader(FileSystem fs,
                   String dirName,
                   Configuration conf)
                    throws IOException

抛出:

IOException

BloomMapFile.Reader

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

抛出:

IOException

BloomMapFile.Reader

public BloomMapFile.Reader(FileSystem fs,
                   String dirName,
                   WritableComparator comparator,
                   Configuration conf)
                    throws IOException

抛出:

IOException

方法详细资料

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.

参数:

key - key to check

返回:

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

抛出:

IOException

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.

覆盖:

get 在类中 MapFile.Reader

抛出:

IOException

getBloomFilter

public Filter getBloomFilter()

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

返回:

a Bloom filter (see Filter)