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

Enclosing class:

BloomMapFile

public static class BloomMapFile.Reader
extends MapFile.Reader

Constructor Summary

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)

Method Summary

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, 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 Detail

BloomMapFile.Reader

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

Throws:

IOException

BloomMapFile.Reader

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

Throws:

IOException

BloomMapFile.Reader

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

Throws:

IOException

Method Detail

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

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

Throws:

IOException

getBloomFilter

public Filter getBloomFilter()

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

Returns:

a Bloom filter (see Filter)