org.apache.hadoop.io

类 MapFile

java.lang.Object

org.apache.hadoop.io.MapFile

直接已知子类:

ArrayFile, SetFile

public class MapFile
extends Object

A file-based map from keys to values.

A map is a directory containing two files, the data file, containing all keys and values in the map, and a smaller index file, containing a fraction of the keys. The fraction is determined by MapFile.Writer.getIndexInterval().

The index file is read entirely into memory. Thus key implementations should try to keep themselves small.

Map files are created by adding entries in-order. To maintain a large database, perform updates by copying the previous version of a database and merging in a sorted change list, to create a new version of the database in a new file. Sorting large change lists can be done with SequenceFile.Sorter.

嵌套类概要

嵌套类

限定符和类型	类和说明
static class	MapFile.Reader Provide access to an existing map.
static class	MapFile.Writer Writes a new map.

字段概要

字段

限定符和类型	字段和说明
static String	DATA_FILE_NAME The name of the data file.
static String	INDEX_FILE_NAME The name of the index file.

构造器概要

构造器

限定符	构造器和说明
protected	MapFile()

方法概要

方法

限定符和类型	方法和说明
static void	delete(FileSystem fs, String name) Deletes the named map file.
static long	fix(FileSystem fs, Path dir, Class<? extends Writable> keyClass, Class<? extends Writable> valueClass, boolean dryrun, Configuration conf) This method attempts to fix a corrupt MapFile by re-creating its index.
static void	main(String[] args)
static void	rename(FileSystem fs, String oldName, String newName) Renames an existing map directory.

从类继承的方法 java.lang.Object

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

字段详细资料

INDEX_FILE_NAME

public static final String INDEX_FILE_NAME

The name of the index file.

另请参阅:

常量字段值

DATA_FILE_NAME

public static final String DATA_FILE_NAME

The name of the data file.

另请参阅:

常量字段值

构造器详细资料

MapFile

protected MapFile()

方法详细资料

rename

public static void rename(FileSystem fs,
          String oldName,
          String newName)
                   throws IOException

Renames an existing map directory.

抛出:

IOException

delete

public static void delete(FileSystem fs,
          String name)
                   throws IOException

Deletes the named map file.

抛出:

IOException

fix

public static long fix(FileSystem fs,
       Path dir,
       Class<? extends Writable> keyClass,
       Class<? extends Writable> valueClass,
       boolean dryrun,
       Configuration conf)
                throws Exception

This method attempts to fix a corrupt MapFile by re-creating its index.

参数:

fs - filesystem

dir - directory containing the MapFile data and index

keyClass - key class (has to be a subclass of Writable)

valueClass - value class (has to be a subclass of Writable)

dryrun - do not perform any changes, just report what needs to be done

返回:

number of valid entries in this MapFile, or -1 if no fixing was needed

抛出:

Exception

main

public static void main(String[] args)
                 throws Exception

抛出:

Exception