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Dec 29, 2015

org.apache.hadoop.filecache
Class DistributedCache

java.lang.Object
  org.apache.hadoop.filecache.DistributedCache

public class DistributedCache
extends Object

Distribute application-specific large, read-only files efficiently.

DistributedCache is a facility provided by the Map-Reduce framework to cache files (text, archives, jars etc.) needed by applications.

Applications specify the files, via urls (hdfs:// or http://) to be cached via the JobConf. The DistributedCache assumes that the files specified via hdfs:// urls are already present on the FileSystem at the path specified by the url.

The framework will copy the necessary files on to the slave node before any tasks for the job are executed on that node. Its efficiency stems from the fact that the files are only copied once per job and the ability to cache archives which are un-archived on the slaves.

DistributedCache can be used to distribute simple, read-only data/text files and/or more complex types such as archives, jars etc. Archives (zip, tar and tgz/tar.gz files) are un-archived at the slave nodes. Jars may be optionally added to the classpath of the tasks, a rudimentary software distribution mechanism. Files have execution permissions. Optionally users can also direct it to symlink the distributed cache file(s) into the working directory of the task.

DistributedCache tracks modification timestamps of the cache files. Clearly the cache files should not be modified by the application or externally while the job is executing.

Here is an illustrative example on how to use the DistributedCache:

     // Setting up the cache for the application
     
     1. Copy the requisite files to the FileSystem:
     
     $ bin/hadoop fs -copyFromLocal lookup.dat /myapp/lookup.dat  
     $ bin/hadoop fs -copyFromLocal map.zip /myapp/map.zip  
     $ bin/hadoop fs -copyFromLocal mylib.jar /myapp/mylib.jar
     $ bin/hadoop fs -copyFromLocal mytar.tar /myapp/mytar.tar
     $ bin/hadoop fs -copyFromLocal mytgz.tgz /myapp/mytgz.tgz
     $ bin/hadoop fs -copyFromLocal mytargz.tar.gz /myapp/mytargz.tar.gz
     
     2. Setup the application's JobConf:
     
     JobConf job = new JobConf();
     DistributedCache.addCacheFile(new URI("/myapp/lookup.dat#lookup.dat"), 
                                   job);
     DistributedCache.addCacheArchive(new URI("/myapp/map.zip", job);
     DistributedCache.addFileToClassPath(new Path("/myapp/mylib.jar"), job);
     DistributedCache.addCacheArchive(new URI("/myapp/mytar.tar", job);
     DistributedCache.addCacheArchive(new URI("/myapp/mytgz.tgz", job);
     DistributedCache.addCacheArchive(new URI("/myapp/mytargz.tar.gz", job);
     
     3. Use the cached files in the Mapper
     or Reducer:
     
     public static class MapClass extends MapReduceBase  
     implements Mapper<K, V, K, V> {
     
       private Path[] localArchives;
       private Path[] localFiles;
       
       public void configure(JobConf job) {
         // Get the cached archives/files
         localArchives = DistributedCache.getLocalCacheArchives(job);
         localFiles = DistributedCache.getLocalCacheFiles(job);
       }
       
       public void map(K key, V value, 
                       OutputCollector<K, V> output, Reporter reporter) 
       throws IOException {
         // Use data from the cached archives/files here
         // ...
         // ...
         output.collect(k, v);
       }
     }
     
 

It is also very common to use the DistributedCache by using GenericOptionsParser. This class includes methods that should be used by users (specifically those mentioned in the example above, as well as addArchiveToClassPath(Path, Configuration)), as well as methods intended for use by the MapReduce framework (e.g., JobClient). For implementation details, see TrackerDistributedCacheManager and TaskDistributedCacheManager.

See Also:

TrackerDistributedCacheManager, TaskDistributedCacheManager, JobConf, JobClient

Field Summary

static String	CACHE_ARCHIVES Warning: CACHE_ARCHIVES is not a *public* constant.
static String	CACHE_ARCHIVES_SIZES Warning: CACHE_ARCHIVES_SIZES is not a *public* constant.
static String	CACHE_ARCHIVES_TIMESTAMPS Warning: CACHE_ARCHIVES_TIMESTAMPS is not a *public* constant.
static String	CACHE_FILES Warning: CACHE_FILES is not a *public* constant.
static String	CACHE_FILES_SIZES Warning: CACHE_FILES_SIZES is not a *public* constant.
static String	CACHE_FILES_TIMESTAMPS Warning: CACHE_FILES_TIMESTAMPS is not a *public* constant.
static String	CACHE_LOCALARCHIVES Warning: CACHE_LOCALARCHIVES is not a *public* constant.
static String	CACHE_LOCALFILES Warning: CACHE_LOCALFILES is not a *public* constant.
static String	CACHE_SYMLINK Warning: CACHE_SYMLINK is not a *public* constant.

Constructor Summary

DistributedCache()

Method Summary

static void	addArchiveToClassPath(Path archive, Configuration conf) Deprecated. Please use addArchiveToClassPath(Path, Configuration, FileSystem) instead. The FileSystem should be obtained within an appropriate doAs.
static void	addArchiveToClassPath(Path archive, Configuration conf, FileSystem fs) Add an archive path to the current set of classpath entries.
static void	addCacheArchive(URI uri, Configuration conf) Add a archives to be localized to the conf.
static void	addCacheFile(URI uri, Configuration conf) Add a file to be localized to the conf.
static void	addFileToClassPath(Path file, Configuration conf) Deprecated. Please use addFileToClassPath(Path, Configuration, FileSystem) instead. The FileSystem should be obtained within an appropriate doAs.
static void	addFileToClassPath(Path file, Configuration conf, FileSystem fs) Add a file path to the current set of classpath entries.
static void	addLocalArchives(Configuration conf, String str) Add a archive that has been localized to the conf.
static void	addLocalFiles(Configuration conf, String str) Add a file that has been localized to the conf..
static boolean	checkURIs(URI[] uriFiles, URI[] uriArchives) This method checks if there is a conflict in the fragment names of the uris.
static void	createAllSymlink(Configuration conf, File jobCacheDir, File workDir) Deprecated. Internal to MapReduce framework. Use DistributedCacheManager instead.
static void	createSymlink(Configuration conf) This method allows you to create symlinks in the current working directory of the task to all the cache files/archives.
static Path[]	getArchiveClassPaths(Configuration conf) Get the archive entries in classpath as an array of Path.
static long[]	getArchiveTimestamps(Configuration conf) Get the timestamps of the archives.
static URI[]	getCacheArchives(Configuration conf) Get cache archives set in the Configuration.
static URI[]	getCacheFiles(Configuration conf) Get cache files set in the Configuration.
static Path[]	getFileClassPaths(Configuration conf) Get the file entries in classpath as an array of Path.
static FileStatus	getFileStatus(Configuration conf, URI cache) Returns FileStatus of a given cache file on hdfs.
static long[]	getFileTimestamps(Configuration conf) Get the timestamps of the files.
static Path[]	getLocalCacheArchives(Configuration conf) Return the path array of the localized caches.
static Path[]	getLocalCacheFiles(Configuration conf) Return the path array of the localized files.
static boolean	getSymlink(Configuration conf) This method checks to see if symlinks are to be create for the localized cache files in the current working directory Used by internal DistributedCache code.
static long	getTimestamp(Configuration conf, URI cache) Returns mtime of a given cache file on hdfs.
static void	setArchiveTimestamps(Configuration conf, String timestamps) This is to check the timestamp of the archives to be localized.
static void	setCacheArchives(URI[] archives, Configuration conf) Set the configuration with the given set of archives.
static void	setCacheFiles(URI[] files, Configuration conf) Set the configuration with the given set of files.
static void	setFileTimestamps(Configuration conf, String timestamps) This is to check the timestamp of the files to be localized.
static void	setLocalArchives(Configuration conf, String str) Set the conf to contain the location for localized archives.
static void	setLocalFiles(Configuration conf, String str) Set the conf to contain the location for localized files.

Methods inherited from class java.lang.Object

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

Field Detail

CACHE_FILES_SIZES

public static final String CACHE_FILES_SIZES

Warning: CACHE_FILES_SIZES is not a *public* constant.

See Also:

Constant Field Values

CACHE_ARCHIVES_SIZES

public static final String CACHE_ARCHIVES_SIZES

Warning: CACHE_ARCHIVES_SIZES is not a *public* constant.

See Also:

Constant Field Values

CACHE_ARCHIVES_TIMESTAMPS

public static final String CACHE_ARCHIVES_TIMESTAMPS

Warning: CACHE_ARCHIVES_TIMESTAMPS is not a *public* constant.

See Also:

Constant Field Values

CACHE_FILES_TIMESTAMPS

public static final String CACHE_FILES_TIMESTAMPS

Warning: CACHE_FILES_TIMESTAMPS is not a *public* constant.

See Also:

Constant Field Values

CACHE_ARCHIVES

public static final String CACHE_ARCHIVES

Warning: CACHE_ARCHIVES is not a *public* constant.

See Also:

Constant Field Values

CACHE_FILES

public static final String CACHE_FILES

Warning: CACHE_FILES is not a *public* constant.

See Also:

Constant Field Values

CACHE_LOCALARCHIVES

public static final String CACHE_LOCALARCHIVES

Warning: CACHE_LOCALARCHIVES is not a *public* constant.

See Also:

Constant Field Values

CACHE_LOCALFILES

public static final String CACHE_LOCALFILES

Warning: CACHE_LOCALFILES is not a *public* constant.

See Also:

Constant Field Values

CACHE_SYMLINK

public static final String CACHE_SYMLINK

Warning: CACHE_SYMLINK is not a *public* constant.

See Also:

Constant Field Values

Constructor Detail

DistributedCache

public DistributedCache()

Method Detail

getFileStatus

public static FileStatus getFileStatus(Configuration conf,
                                       URI cache)
                                throws IOException

Returns FileStatus of a given cache file on hdfs. Internal to MapReduce.

Parameters:

conf - configuration

cache - cache file

Returns:

FileStatus of a given cache file on hdfs

Throws:

IOException

getTimestamp

public static long getTimestamp(Configuration conf,
                                URI cache)
                         throws IOException

Returns mtime of a given cache file on hdfs. Internal to MapReduce.

Parameters:

conf - configuration

cache - cache file

Returns:

mtime of a given cache file on hdfs

Throws:

IOException

createAllSymlink

public static void createAllSymlink(Configuration conf,
                                    File jobCacheDir,
                                    File workDir)
                             throws IOException

Deprecated. Internal to MapReduce framework. Use DistributedCacheManager instead.

This method create symlinks for all files in a given dir in another directory

Parameters:

conf - the configuration

jobCacheDir - the target directory for creating symlinks

workDir - the directory in which the symlinks are created

Throws:

IOException

setCacheArchives

public static void setCacheArchives(URI[] archives,
                                    Configuration conf)

Set the configuration with the given set of archives. Intended to be used by user code.

Parameters:

archives - The list of archives that need to be localized

conf - Configuration which will be changed

setCacheFiles

public static void setCacheFiles(URI[] files,
                                 Configuration conf)

Set the configuration with the given set of files. Intended to be used by user code.

Parameters:

files - The list of files that need to be localized

conf - Configuration which will be changed

getCacheArchives

public static URI[] getCacheArchives(Configuration conf)
                              throws IOException

Get cache archives set in the Configuration. Used by internal DistributedCache and MapReduce code.

Parameters:

conf - The configuration which contains the archives

Returns:

An array of the caches set in the Configuration

Throws:

IOException

getCacheFiles

public static URI[] getCacheFiles(Configuration conf)
                           throws IOException

Get cache files set in the Configuration. Used by internal DistributedCache and MapReduce code.

Parameters:

conf - The configuration which contains the files

Returns:

Am array of the files set in the Configuration

Throws:

IOException

getLocalCacheArchives

public static Path[] getLocalCacheArchives(Configuration conf)
                                    throws IOException

Return the path array of the localized caches. Intended to be used by user code.

Parameters:

conf - Configuration that contains the localized archives

Returns:

A path array of localized caches

Throws:

IOException

getLocalCacheFiles

public static Path[] getLocalCacheFiles(Configuration conf)
                                 throws IOException

Return the path array of the localized files. Intended to be used by user code.

Parameters:

conf - Configuration that contains the localized files

Returns:

A path array of localized files

Throws:

IOException

getArchiveTimestamps

public static long[] getArchiveTimestamps(Configuration conf)

Get the timestamps of the archives. Used by internal DistributedCache and MapReduce code.

Parameters:

conf - The configuration which stored the timestamps

Returns:

a long array of timestamps

Throws:

IOException

getFileTimestamps

public static long[] getFileTimestamps(Configuration conf)

Get the timestamps of the files. Used by internal DistributedCache and MapReduce code.

Parameters:

conf - The configuration which stored the timestamps

Returns:

a long array of timestamps

Throws:

IOException

setArchiveTimestamps

public static void setArchiveTimestamps(Configuration conf,
                                        String timestamps)

This is to check the timestamp of the archives to be localized. Used by internal MapReduce code.

Parameters:

conf - Configuration which stores the timestamp's

timestamps - comma separated list of timestamps of archives. The order should be the same as the order in which the archives are added.

setFileTimestamps

public static void setFileTimestamps(Configuration conf,
                                     String timestamps)

This is to check the timestamp of the files to be localized. Used by internal MapReduce code.

Parameters:

conf - Configuration which stores the timestamp's

timestamps - comma separated list of timestamps of files. The order should be the same as the order in which the files are added.

setLocalArchives

public static void setLocalArchives(Configuration conf,
                                    String str)

Set the conf to contain the location for localized archives. Used by internal DistributedCache code.

Parameters:

conf - The conf to modify to contain the localized caches

str - a comma separated list of local archives

setLocalFiles

public static void setLocalFiles(Configuration conf,
                                 String str)

Set the conf to contain the location for localized files. Used by internal DistributedCache code.

Parameters:

conf - The conf to modify to contain the localized caches

str - a comma separated list of local files

addLocalArchives

public static void addLocalArchives(Configuration conf,
                                    String str)

Add a archive that has been localized to the conf. Used by internal DistributedCache code.

Parameters:

conf - The conf to modify to contain the localized caches

str - a comma separated list of local archives

addLocalFiles

public static void addLocalFiles(Configuration conf,
                                 String str)

Add a file that has been localized to the conf.. Used by internal DistributedCache code.

Parameters:

conf - The conf to modify to contain the localized caches

str - a comma separated list of local files

addCacheArchive

public static void addCacheArchive(URI uri,
                                   Configuration conf)

Add a archives to be localized to the conf. Intended to be used by user code.

Parameters:

uri - The uri of the cache to be localized

conf - Configuration to add the cache to

addCacheFile

public static void addCacheFile(URI uri,
                                Configuration conf)

Add a file to be localized to the conf. Intended to be used by user code.

Parameters:

uri - The uri of the cache to be localized

conf - Configuration to add the cache to

addFileToClassPath

@Deprecated
public static void addFileToClassPath(Path file,
                                                 Configuration conf)
                               throws IOException

Deprecated. Please use addFileToClassPath(Path, Configuration, FileSystem) instead. The FileSystem should be obtained within an appropriate doAs.

Add a file path to the current set of classpath entries. It adds the file to cache as well. Intended to be used by user code.

Parameters:

file - Path of the file to be added

conf - Configuration that contains the classpath setting

Throws:

IOException

addFileToClassPath

public static void addFileToClassPath(Path file,
                                      Configuration conf,
                                      FileSystem fs)
                               throws IOException

Add a file path to the current set of classpath entries. It adds the file to cache as well. Intended to be used by user code.

Parameters:

file - Path of the file to be added

conf - Configuration that contains the classpath setting

fs - FileSystem with respect to which archivefile should be interpreted.

Throws:

IOException

getFileClassPaths

public static Path[] getFileClassPaths(Configuration conf)

Get the file entries in classpath as an array of Path. Used by internal DistributedCache code.

Parameters:

conf - Configuration that contains the classpath setting

addArchiveToClassPath

@Deprecated
public static void addArchiveToClassPath(Path archive,
                                                    Configuration conf)
                                  throws IOException

Deprecated. Please use addArchiveToClassPath(Path, Configuration, FileSystem) instead. The FileSystem should be obtained within an appropriate doAs.

Add an archive path to the current set of classpath entries. It adds the archive to cache as well. Intended to be used by user code.

Parameters:

archive - Path of the archive to be added

conf - Configuration that contains the classpath setting

Throws:

IOException

addArchiveToClassPath

public static void addArchiveToClassPath(Path archive,
                                         Configuration conf,
                                         FileSystem fs)
                                  throws IOException

Add an archive path to the current set of classpath entries. It adds the archive to cache as well. Intended to be used by user code.

Parameters:

archive - Path of the archive to be added

conf - Configuration that contains the classpath setting

fs - FileSystem with respect to which archive should be interpreted.

Throws:

IOException

getArchiveClassPaths

public static Path[] getArchiveClassPaths(Configuration conf)

Get the archive entries in classpath as an array of Path. Used by internal DistributedCache code.

Parameters:

conf - Configuration that contains the classpath setting

createSymlink

public static void createSymlink(Configuration conf)

This method allows you to create symlinks in the current working directory of the task to all the cache files/archives. Intended to be used by user code.

Parameters:

conf - the jobconf

getSymlink

public static boolean getSymlink(Configuration conf)

This method checks to see if symlinks are to be create for the localized cache files in the current working directory Used by internal DistributedCache code.

Parameters:

conf - the jobconf

Returns:

true if symlinks are to be created- else return false

checkURIs

public static boolean checkURIs(URI[] uriFiles,
                                URI[] uriArchives)

This method checks if there is a conflict in the fragment names of the uris. Also makes sure that each uri has a fragment. It is only to be called if you want to create symlinks for the various archives and files. May be used by user code.

Parameters:

uriFiles - The uri array of urifiles

uriArchives - the uri array of uri archives