true if the key is deprecated and
+ false otherwise.]]>
+ null if
+ no such property exists. If the key is deprecated, it returns the value of
+ the first key which replaces the deprecated key and is not null.
+
+ Values are processed for variable expansion
+ before being returned.
+
+ @param name the property name, will be trimmed before get value.
+ @return the value of the name or its replacing property,
+ or null if no such property exists.]]>
+ String,
+ null if no such property exists.
+ If the key is deprecated, it returns the value of
+ the first key which replaces the deprecated key and is not null
+
+ Values are processed for variable expansion
+ before being returned.
+
+ @param name the property name.
+ @return the value of the name or its replacing property,
+ or null if no such property exists.]]>
+ String,
+ defaultValue if no such property exists.
+ See @{Configuration#getTrimmed} for more details.
+
+ @param name the property name.
+ @param defaultValue the property default value.
+ @return the value of the name or defaultValue
+ if it is not set.]]>
+ name property or
+ its replacing property and null if no such property exists.]]>
+ name property. If
+ name is deprecated or there is a deprecated name associated to it,
+ it sets the value to both names. Name will be trimmed before put into
+ configuration.
+
+ @param name property name.
+ @param value property value.]]>
+ name property. If
+ name is deprecated, it also sets the value to
+ the keys that replace the deprecated key. Name will be trimmed before put
+ into configuration.
+
+ @param name property name.
+ @param value property value.
+ @param source the place that this configuration value came from
+ (For debugging).
+ @throws IllegalArgumentException when the value or name is null.]]>
+ defaultValue is returned.
+
+ @param name property name, will be trimmed before get value.
+ @param defaultValue default value.
+ @return property value, or defaultValue if the property
+ doesn't exist.]]>
+ int.
+
+ If no such property exists, the provided default value is returned,
+ or if the specified value is not a valid int,
+ then an error is thrown.
+
+ @param name property name.
+ @param defaultValue default value.
+ @throws NumberFormatException when the value is invalid
+ @return property value as an int,
+ or defaultValue.]]>
+ int values.
+
+ If no such property exists, an empty array is returned.
+
+ @param name property name
+ @return property value interpreted as an array of comma-delimited
+ int values]]>
+ int.
+
+ @param name property name.
+ @param value int value of the property.]]>
+ long.
+ If no such property exists, the provided default value is returned,
+ or if the specified value is not a valid long,
+ then an error is thrown.
+
+ @param name property name.
+ @param defaultValue default value.
+ @throws NumberFormatException when the value is invalid
+ @return property value as a long,
+ or defaultValue.]]>
+ long or
+ human readable format. If no such property exists, the provided default
+ value is returned, or if the specified value is not a valid
+ long or human readable format, then an error is thrown. You
+ can use the following suffix (case insensitive): k(kilo), m(mega), g(giga),
+ t(tera), p(peta), e(exa)
+
+ @param name property name.
+ @param defaultValue default value.
+ @throws NumberFormatException when the value is invalid
+ @return property value as a long,
+ or defaultValue.]]>
+ long.
+
+ @param name property name.
+ @param value long value of the property.]]>
+ float.
+ If no such property exists, the provided default value is returned,
+ or if the specified value is not a valid float,
+ then an error is thrown.
+
+ @param name property name.
+ @param defaultValue default value.
+ @throws NumberFormatException when the value is invalid
+ @return property value as a float,
+ or defaultValue.]]>
+ float.
+
+ @param name property name.
+ @param value property value.]]>
+ double.
+ If no such property exists, the provided default value is returned,
+ or if the specified value is not a valid double,
+ then an error is thrown.
+
+ @param name property name.
+ @param defaultValue default value.
+ @throws NumberFormatException when the value is invalid
+ @return property value as a double,
+ or defaultValue.]]>
+ double.
+
+ @param name property name.
+ @param value property value.]]>
+ boolean.
+ If no such property is specified, or if the specified value is not a valid
+ boolean, then defaultValue is returned.
+
+ @param name property name.
+ @param defaultValue default value.
+ @return property value as a boolean,
+ or defaultValue.]]>
+ boolean.
+
+ @param name property name.
+ @param value boolean value of the property.]]>
+ set(<name>, value.toString()).
+ @param name property name
+ @param value new value]]>
+ set(<name>, value + <time suffix>).
+ @param name Property name
+ @param value Time duration
+ @param unit Unit of time]]>
+ Pattern.
+ If no such property is specified, or if the specified value is not a valid
+ Pattern, then DefaultValue is returned.
+
+ @param name property name
+ @param defaultValue default value
+ @return property value as a compiled Pattern, or defaultValue]]>
+ Strings.
+ If no such property is specified then empty collection is returned.
+
+ This is an optimized version of {@link #getStrings(String)}
+
+ @param name property name.
+ @return property value as a collection of Strings.]]>
+
Strings.
+ If no such property is specified then null is returned.
+
+ @param name property name.
+ @return property value as an array of Strings,
+ or null.]]>
+ Strings.
+ If no such property is specified then default value is returned.
+
+ @param name property name.
+ @param defaultValue The default value
+ @return property value as an array of Strings,
+ or default value.]]>
+ Strings, trimmed of the leading and trailing whitespace.
+ If no such property is specified then empty Collection is returned.
+
+ @param name property name.
+ @return property value as a collection of Strings, or empty Collection]]>
+ Strings, trimmed of the leading and trailing whitespace.
+ If no such property is specified then an empty array is returned.
+
+ @param name property name.
+ @return property value as an array of trimmed Strings,
+ or empty array.]]>
+ Strings, trimmed of the leading and trailing whitespace.
+ If no such property is specified then default value is returned.
+
+ @param name property name.
+ @param defaultValue The default value
+ @return property value as an array of trimmed Strings,
+ or default value.]]>
+ InetSocketAddress. If hostProperty is
+ null, addressProperty will be used. This
+ is useful for cases where we want to differentiate between host
+ bind address and address clients should use to establish connection.
+
+ @param hostProperty bind host property name.
+ @param addressProperty address property name.
+ @param defaultAddressValue the default value
+ @param defaultPort the default port
+ @return InetSocketAddress]]>
+ InetSocketAddress.
+ @param name property name.
+ @param defaultAddress the default value
+ @param defaultPort the default port
+ @return InetSocketAddress]]>
+ host:port.]]>
+ host:port. The wildcard
+ address is replaced with the local host's address. If the host and address
+ properties are configured the host component of the address will be combined
+ with the port component of the addr to generate the address. This is to allow
+ optional control over which host name is used in multi-home bind-host
+ cases where a host can have multiple names
+ @param hostProperty the bind-host configuration name
+ @param addressProperty the service address configuration name
+ @param defaultAddressValue the service default address configuration value
+ @param addr InetSocketAddress of the service listener
+ @return InetSocketAddress for clients to connect]]>
+ host:port. The wildcard
+ address is replaced with the local host's address.
+ @param name property name.
+ @param addr InetSocketAddress of a listener to store in the given property
+ @return InetSocketAddress for clients to connect]]>
+ Class.
+ The value of the property specifies a list of comma separated class names.
+ If no such property is specified, then defaultValue is
+ returned.
+
+ @param name the property name.
+ @param defaultValue default value.
+ @return property value as a Class[],
+ or defaultValue.]]>
+ Class.
+ If no such property is specified, then defaultValue is
+ returned.
+
+ @param name the class name.
+ @param defaultValue default value.
+ @return property value as a Class,
+ or defaultValue.]]>
+ Class
+ implementing the interface specified by xface.
+
+ If no such property is specified, then defaultValue is
+ returned.
+
+ An exception is thrown if the returned class does not implement the named
+ interface.
+
+ @param name the class name.
+ @param defaultValue default value.
+ @param xface the interface implemented by the named class.
+ @return property value as a Class,
+ or defaultValue.]]>
+ List
+ of objects implementing the interface specified by xface.
+
+ An exception is thrown if any of the classes does not exist, or if it does
+ not implement the named interface.
+
+ @param name the property name.
+ @param xface the interface implemented by the classes named by
+ name.
+ @return a List of objects implementing xface.]]>
+ theClass implementing the given interface xface.
+
+ An exception is thrown if theClass does not implement the
+ interface xface.
+
+ @param name property name.
+ @param theClass property value.
+ @param xface the interface implemented by the named class.]]>
+ false
+ to turn it off.]]>
+ Configurations are specified by resources. A resource contains a set of
+ name/value pairs as XML data. Each resource is named by either a
+ String or by a {@link Path}. If named by a String,
+ then the classpath is examined for a file with that name. If named by a
+ Path, then the local filesystem is examined directly, without
+ referring to the classpath.
+
+
Unless explicitly turned off, Hadoop by default specifies two + resources, loaded in-order from the classpath:
Configuration parameters may be declared final.
+ Once a resource declares a value final, no subsequently-loaded
+ resource can alter that value.
+ For example, one might define a final parameter with:
+
+ <property>
+ <name>dfs.hosts.include</name>
+ <value>/etc/hadoop/conf/hosts.include</value>
+ <final>true</final>
+ </property>
+
+ Administrators typically define parameters as final in
+ core-site.xml for values that user applications may not alter.
+
+
Value strings are first processed for variable expansion. The + available properties are:
For example, if a configuration resource contains the following property
+ definitions:
+
+ <property>
+ <name>basedir</name>
+ <value>/user/${user.name}</value>
+ </property>
+
+ <property>
+ <name>tempdir</name>
+ <value>${basedir}/tmp</value>
+ </property>
+
+ When conf.get("tempdir") is called, then ${basedir}
+ will be resolved to another property in this Configuration, while
+ ${user.name} would then ordinarily be resolved to the value
+ of the System property with that name.
+ By default, warnings will be given to any deprecated configuration
+ parameters and these are suppressible by configuring
+ log4j.logger.org.apache.hadoop.conf.Configuration.deprecation in
+ log4j.properties file.]]>
+
KeyVersions and Metadatato avoid burst
+ of requests to hit the underlying KeyProvider.]]>
+ KeyProvider implementations must be thread safe.]]>
+ KeyProvider
+
+ @param encryptionKeyName
+ The latest KeyVersion of this key's material will be encrypted.
+ @return EncryptedKeyVersion with the generated key material, the version
+ name is 'EEK' (for Encrypted Encryption Key)
+ @throws IOException
+ thrown if the key material could not be generated
+ @throws GeneralSecurityException
+ thrown if the key material could not be encrypted because of a
+ cryptographic issue.]]>
+ KeyProvider implements the
+ {@link DelegationTokenExtension} interface the KeyProvider
+ itself will provide the extension functionality, otherwise a default
+ extension implementation will be used.
+
+ @param keyProvider KeyProvider to use to create the
+ KeyProviderDelegationTokenExtension extension.
+ @return a KeyProviderDelegationTokenExtension instance
+ using the given KeyProvider.]]>
+ uri is not supported.]]>
+
+ EnumSet.of(CreateFlag.CREATE, CreateFlag.APPEND)
+
+
+
+ Use the CreateFlag as follows:
+
+ - CREATE - to create a file if it does not exist,
+ else throw FileAlreadyExists.
+ - APPEND - to append to a file if it exists,
+ else throw FileNotFoundException.
+ - OVERWRITE - to truncate a file if it exists,
+ else throw FileNotFoundException.
+ - CREATE|APPEND - to create a file if it does not exist,
+ else append to an existing file.
+ - CREATE|OVERWRITE - to create a file if it does not exist,
+ else overwrite an existing file.
+ - SYNC_BLOCK - to force closed blocks to the disk device.
+ In addition {@link Syncable#hsync()} should be called after each write,
+ if true synchronous behavior is required.
+
+
+ Following combination is not valid and will result in
+ {@link HadoopIllegalArgumentException}:
+
+ - APPEND|OVERWRITE
+ - CREATE|APPEND|OVERWRITE
+
]]>
+ absOrFqPath could
+ not be instantiated.]]>
+ f is not valid]]>
+ f already exists
+ @throws FileNotFoundException If parent of f does not exist
+ and createParent is false
+ @throws ParentNotDirectoryException If parent of f is not a
+ directory.
+ @throws UnsupportedFileSystemException If file system for f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws InvalidPathException If path f is not valid]]>
+ dir does not exist
+ and createParent is false
+ @throws ParentNotDirectoryException If parent of dir is not a
+ directory
+ @throws UnsupportedFileSystemException If file system for dir
+ is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws InvalidPathException If path dir is not valid]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws InvalidPathException If path f is invalid]]>
+ f
+ is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ + If OVERWRITE option is not passed as an argument, rename fails if the dst + already exists. +
+ If OVERWRITE option is passed as an argument, rename overwrites the dst if + it is a file or an empty directory. Rename fails if dst is a non-empty + directory. +
+ Note that atomicity of rename is dependent on the file system + implementation. Please refer to the file system documentation for details +
+
+ @param src path to be renamed
+ @param dst new path after rename
+
+ @throws AccessControlException If access is denied
+ @throws FileAlreadyExistsException If dst already exists and
+ options has {@link Options.Rename#OVERWRITE}
+ option false.
+ @throws FileNotFoundException If src does not exist
+ @throws ParentNotDirectoryException If parent of dst is not a
+ directory
+ @throws UnsupportedFileSystemException If file system for src
+ and dst is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+
f
+ is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws HadoopIllegalArgumentException If username or
+ groupname is invalid.]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+
+ In general, applications should avoid using this method, due to the risk of
+ time-of-check/time-of-use race conditions. The permissions on a file may
+ change immediately after the access call returns. Most applications should
+ prefer running specific file system actions as the desired user represented
+ by a {@link UserGroupInformation}.
+
+ @param path Path to check
+ @param mode type of access to check
+ @throws AccessControlException if access is denied
+ @throws FileNotFoundException if the path does not exist
+ @throws UnsupportedFileSystemException if file system for path
+ is not supported
+ @throws IOException see specific implementation
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+
f is
+ not supported
+ @throws IOException If an I/O error occurred]]>
+ f is
+ not supported
+ @throws IOException If the given path does not refer to a symlink
+ or an I/O error occurred]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws InvalidPathException If path f is invalid]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ linkcode> already exists
+ @throws FileNotFoundException If target does not exist
+ @throws ParentNotDirectoryException If parent of link is not a
+ directory.
+ @throws UnsupportedFileSystemException If file system for
+ target or link is not supported
+ @throws IOException If an I/O error occurred]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ + + The Hadoop file system supports a URI name space and URI names. + It offers a forest of file systems that can be referenced using fully + qualified URIs. + Two common Hadoop file systems implementations are +
+ + To facilitate this, Hadoop supports a notion of a default file system. + The user can set his default file system, although this is + typically set up for you in your environment via your default config. + A default file system implies a default scheme and authority; slash-relative + names (such as /for/bar) are resolved relative to that default FS. + Similarly a user can also have working-directory-relative names (i.e. names + not starting with a slash). While the working directory is generally in the + same default FS, the wd can be in a different FS. +
+ Hence Hadoop path names can be one of: +
+ ****The Role of the FileContext and configuration defaults**** +
+ The FileContext provides file namespace context for resolving file names; + it also contains the umask for permissions, In that sense it is like the + per-process file-related state in Unix system. + These two properties +
+ The file system related SS defaults are +
+ *** Usage Model for the FileContext class *** +
+ Example 1: use the default config read from the $HADOOP_CONFIG/core.xml. + Unspecified values come from core-defaults.xml in the release jar. +
f is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ pathPattern is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f is
+ not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ f
+ is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ + A filename pattern is composed of regular characters and + special pattern matching characters, which are: + +
+
+
+
+
+
+
+
+
pathPattern is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server]]>
+ src does not exist
+ @throws ParentNotDirectoryException If parent of dst is not
+ a directory
+ @throws UnsupportedFileSystemException If file system for
+ src or dst is not supported
+ @throws IOException If an I/O error occurred
+
+ Exceptions applicable to file systems accessed over RPC:
+ @throws RpcClientException If an exception occurred in the RPC client
+ @throws RpcServerException If an exception occurred in the RPC server
+ @throws UnexpectedServerException If server implementation throws
+ undeclared exception to RPC server
+
+ RuntimeExceptions:
+ @throws InvalidPathException If path dst is invalid]]>
+ UnsupportedOperationException.
+
+ @return the protocol scheme for the FileSystem.]]>
+ + If OVERWRITE option is not passed as an argument, rename fails + if the dst already exists. +
+ If OVERWRITE option is passed as an argument, rename overwrites + the dst if it is a file or an empty directory. Rename fails if dst is + a non-empty directory. +
+ Note that atomicity of rename is dependent on the file system + implementation. Please refer to the file system documentation for + details. This default implementation is non atomic. +
+ This method is deprecated since it is a temporary method added to + support the transition from FileSystem to FileContext for user + applications. + + @param src path to be renamed + @param dst new path after rename + @throws IOException on failure]]> +
+ A filename pattern is composed of regular characters and + special pattern matching characters, which are: + +
+
+
+
+
+
+
+
+
+ In general, applications should avoid using this method, due to the risk of + time-of-check/time-of-use race conditions. The permissions on a file may + change immediately after the access call returns. Most applications should + prefer running specific file system actions as the desired user represented + by a {@link UserGroupInformation}. + + @param path Path to check + @param mode type of access to check + @throws AccessControlException if access is denied + @throws FileNotFoundException if the path does not exist + @throws IOException see specific implementation]]> +
+ The local implementation is {@link LocalFileSystem} and distributed + implementation is DistributedFileSystem.]]> +
FilterFileSystem
+ itself simply overrides all methods of
+ FileSystem with versions that
+ pass all requests to the contained file
+ system. Subclasses of FilterFileSystem
+ may further override some of these methods
+ and may also provide additional methods
+ and fields.]]>
+ har]]>
+ file]]>
+ pathname
+ should be included]]>
+ ftp]]>
+ viewfs]]>
+ + To use viewfs one would typically set the default file system in the + config (i.e. fs.default.name< = viewfs:///) along with the + mount table config variables as described below. + +
+ ** Config variables to specify the mount table entries ** +
+ + The file system is initialized from the standard Hadoop config through + config variables. + See {@link FsConstants} for URI and Scheme constants; + See {@link Constants} for config var constants; + see {@link ConfigUtil} for convenient lib. + +
+ All the mount table config entries for view fs are prefixed by + fs.viewfs.mounttable. + For example the above example can be specified with the following + config variables: +
+ **** Merge Mounts **** (NOTE: merge mounts are not implemented yet.) +
+ + One can also use "MergeMounts" to merge several directories (this is + sometimes called union-mounts or junction-mounts in the literature. + For example of the home directories are stored on say two file systems + (because they do not fit on one) then one could specify a mount + entry such as following merges two dirs: +
+ Fencing is configured by the operator as an ordered list of methods to + attempt. Each method will be tried in turn, and the next in the list + will only be attempted if the previous one fails. See {@link NodeFencer} + for more information. +
+ If an implementation also implements {@link Configurable} then its
+ setConf method will be called upon instantiation.]]>
+
+ shell(/path/to/my/script.sh arg1 arg2 ...)
+ + + The shell command will be run with an environment set up to contain + all of the current Hadoop configuration variables, with the '_' character + replacing any '.' characters in the configuration keys.
+ + If the shell command returns an exit code of 0, the fencing is + determined to be successful. If it returns any other exit code, the + fencing was not successful and the next fencing method in the list + will be attempted.
+ + Note: this fencing method does not implement any timeout. + If timeouts are necessary, they should be implemented in the shell + script itself (eg by forking a subshell to kill its parent in + some number of seconds).]]> +
+ It returns a successful status code if: +
fuser indicates it successfully killed a process, or
+ nc -z indicates that nothing is listening on the target port
+
+ This fencing mechanism is configured as following in the fencing method
+ list:
+ sshfence([[username][:ssh-port]])
+ where the optional argument specifies the username and port to use
+ with ssh.
+
+ In order to achieve passwordless SSH, the operator must also configure
+ dfs.ha.fencing.ssh.private-key-files to point to an
+ SSH key that has passphrase-less access to the given username and host.]]>
+
+ Compared with ObjectWritable, this class is much more effective,
+ because ObjectWritable will append the class declaration as a String
+ into the output file in every Key-Value pair.
+
+ Generic Writable implements {@link Configurable} interface, so that it will be + configured by the framework. The configuration is passed to the wrapped objects + implementing {@link Configurable} interface before deserialization. +
+ + how to use it:getTypes(), defines
+ the classes which will be wrapped in GenericObject in application.
+ Attention: this classes defined in getTypes() method, must
+ implement Writable interface.
+
+ public class GenericObject extends GenericWritable {
+
+ private static Class[] CLASSES = {
+ ClassType1.class,
+ ClassType2.class,
+ ClassType3.class,
+ };
+
+ protected Class[] getTypes() {
+ return CLASSES;
+ }
+
+ }
+ 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
+ {@link 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 {@link + SequenceFile.Sorter}.]]> +
val. Returns true if such a pair exists and false when at
+ the end of the map]]>
+ key. Otherwise,
+ return the record that sorts just after.
+ @return - the key that was the closest match or null if eof.]]>
+ SequenceFile provides {@link SequenceFile.Writer},
+ {@link SequenceFile.Reader} and {@link Sorter} classes for writing,
+ reading and sorting respectively.
SequenceFile Writers based on the
+ {@link CompressionType} used to compress key/value pairs:
+ Writer : Uncompressed records.
+ RecordCompressWriter : Record-compressed files, only compress
+ values.
+ BlockCompressWriter : Block-compressed files, both keys &
+ values are collected in 'blocks'
+ separately and compressed. The size of
+ the 'block' is configurable.
+ The actual compression algorithm used to compress key and/or values can be + specified by using the appropriate {@link CompressionCodec}.
+ +The recommended way is to use the static createWriter methods
+ provided by the SequenceFile to chose the preferred format.
The {@link SequenceFile.Reader} acts as the bridge and can read any of the
+ above SequenceFile formats.
Essentially there are 3 different formats for SequenceFiles
+ depending on the CompressionType specified. All of them share a
+ common header described below.
+
+
CompressionCodec class which is used for
+ compression of keys and/or values (if compression is
+ enabled).
+ 100 bytes or so.
+ 100 bytes or so.
+ The compressed blocks of key lengths and value lengths consist of the + actual lengths of individual keys/values encoded in ZeroCompressedInteger + format.
+ + @see CompressionCodec]]> +val. Returns true if such a pair exists and false when at
+ end of file]]>
+ key, or null if no match exists.]]>
+ start. The starting
+ position is measured in bytes and the return value is in
+ terms of byte position in the buffer. The backing buffer is
+ not converted to a string for this operation.
+ @return byte position of the first occurence of the search
+ string in the UTF-8 buffer or -1 if not found]]>
+ new byte[0]).]]>
+ Also includes utilities for + serializing/deserialing a string, coding/decoding a string, checking if a + byte array contains valid UTF8 code, calculating the length of an encoded + string.]]> +
DataOuput to serialize this object into.
+ @throws IOException]]>
+ For efficiency, implementations should attempt to re-use storage in the + existing object where possible.
+ + @param inDataInput to deseriablize this object from.
+ @throws IOException]]>
+ key or value type in the Hadoop Map-Reduce
+ framework implements this interface.
+
+ Implementations typically implement a static read(DataInput)
+ method which constructs a new instance, calls {@link #readFields(DataInput)}
+ and returns the instance.
Example:
+
+ public class MyWritable implements Writable {
+ // Some data
+ private int counter;
+ private long timestamp;
+
+ public void write(DataOutput out) throws IOException {
+ out.writeInt(counter);
+ out.writeLong(timestamp);
+ }
+
+ public void readFields(DataInput in) throws IOException {
+ counter = in.readInt();
+ timestamp = in.readLong();
+ }
+
+ public static MyWritable read(DataInput in) throws IOException {
+ MyWritable w = new MyWritable();
+ w.readFields(in);
+ return w;
+ }
+ }
+ WritableComparables can be compared to each other, typically
+ via Comparators. Any type which is to be used as a
+ key in the Hadoop Map-Reduce framework should implement this
+ interface.
+
+ Note that hashCode() is frequently used in Hadoop to partition
+ keys. It's important that your implementation of hashCode() returns the same
+ result across different instances of the JVM. Note also that the default
+ hashCode() implementation in Object does not
+ satisfy this property.
Example:
+]]> ++ public class MyWritableComparable implements WritableComparable{ + // Some data + private int counter; + private long timestamp; + + public void write(DataOutput out) throws IOException { + out.writeInt(counter); + out.writeLong(timestamp); + } + + public void readFields(DataInput in) throws IOException { + counter = in.readInt(); + timestamp = in.readLong(); + } + + public int compareTo(MyWritableComparable o) { + int thisValue = this.value; + int thatValue = o.value; + return (thisValue < thatValue ? -1 : (thisValue==thatValue ? 0 : 1)); + } + + public int hashCode() { + final int prime = 31; + int result = 1; + result = prime * result + counter; + result = prime * result + (int) (timestamp ^ (timestamp >>> 32)); + return result + } + } +
One may optimize compare-intensive operations by overriding + {@link #compare(byte[],int,int,byte[],int,int)}. Static utility methods are + provided to assist in optimized implementations of this method.]]> +
Compressor
+ @param conf the Configuration object which contains confs for creating or reinit the compressor
+ @return Compressor for the given
+ CompressionCodec from the pool or a new one]]>
+ Decompressor
+ @return Decompressor for the given
+ CompressionCodec the pool or a new one]]>
+ b[] remain unmodified until
+ the caller is explicitly notified--via {@link #needsInput()}--that the
+ buffer may be safely modified. With this requirement, an extra
+ buffer-copy can be avoided.)
+
+ @param b Input data
+ @param off Start offset
+ @param len Length]]>
+ true if the input data buffer is empty and
+ {@link #setInput(byte[], int, int)} should be called in
+ order to provide more input.]]>
+ true if a preset dictionary is needed for decompression]]>
+ true and {@link #getRemaining()}
+ returns a positive value. finished() will be reset with the
+ {@link #reset()} method.
+ @return true if the end of the decompressed
+ data output stream has been reached.]]>
+ true and getRemaining() returns
+ a zero value, indicates that the end of data stream has been reached and
+ is not a concatenated data stream.
+ @return The number of bytes remaining in the compressed data buffer.]]>
+ false when reset() is called.]]>
+ + The behavior of TFile can be customized by the following variables through + Configuration: +
+ Suggestions on performance optimization. +
+ Use {@link Scanner#advance()} to move the cursor to the next key-value + pair (or end if none exists). Use seekTo methods ( + {@link Scanner#seekTo(byte[])} or + {@link Scanner#seekTo(byte[], int, int)}) to seek to any arbitrary + location in the covered range (including backward seeking). Use + {@link Scanner#rewind()} to seek back to the beginning of the scanner. + Use {@link Scanner#seekToEnd()} to seek to the end of the scanner. +
+ Actual keys and values may be obtained through {@link Scanner.Entry} + object, which is obtained through {@link Scanner#entry()}.]]> +
+To add a new serialization framework write an implementation of +{@link org.apache.hadoop.io.serializer.Serialization} and add its name to the +"io.serializations" property. +
]]> ++Use {@link org.apache.hadoop.io.serializer.avro.AvroSpecificSerialization} for +serialization of classes generated by Avro's 'specific' compiler. +
+ ++Use {@link org.apache.hadoop.io.serializer.avro.AvroReflectSerialization} for +other classes. +{@link org.apache.hadoop.io.serializer.avro.AvroReflectSerialization} work for +any class which is either in the package list configured via +{@link org.apache.hadoop.io.serializer.avro.AvroReflectSerialization#AVRO_REFLECT_PACKAGES} +or implement {@link org.apache.hadoop.io.serializer.avro.AvroReflectSerializable} +interface. +
]]> +qry parameter
+ may be used to query only a subset of the JMX Beans. This query
+ functionality is provided through the
+ {@link MBeanServer#queryNames(ObjectName, javax.management.QueryExp)}
+ method.
+
+ For example http://.../jmx?qry=Hadoop:* will return
+ all hadoop metrics exposed through JMX.
+
+ The optional
+ For example
+
+ If the
+ If a resouce such as a mbean or attribute can not be found,
+ a 404 SC_NOT_FOUND http response code will be returned.
+
+ The return format is JSON and in the form
+
+
+ The servlet attempts to convert the the JMXBeans into JSON. Each
+ bean's attributes will be converted to a JSON object member.
+
+ If the attribute is a boolean, a number, a string, or an array
+ it will be converted to the JSON equivalent.
+
+ If the value is a {@link CompositeData} then it will be converted
+ to a JSON object with the keys as the name of the JSON member and
+ the value is converted following these same rules.
+
+ If the value is a {@link TabularData} then it will be converted
+ to an array of the {@link CompositeData} elements that it contains.
+
+ All other objects will be converted to a string and output as such.
+
+ The bean's name and modelerType will be returned for all beans.
+
+ Optional paramater "callback" should be used to deliver JSONP response.]]>
+ get parameter is used to query an specific
+ attribute of a JMX bean. The format of the URL is
+ http://.../jmx?get=MXBeanName::AttributeName
+
+ http://../jmx?get=Hadoop:service=NameNode,name=NameNodeInfo::ClusterId
+ will return the cluster id of the namenode mxbean.
+ qry or the get parameter is not formatted
+ correctly then a 400 BAD REQUEST http response code will be returned.
+
+ {
+ "beans" : [
+ {
+ "name":"bean-name"
+ ...
+ }
+ ]
+ }
+
+ {"name":"test","time":1318429136789,"date":"2011-10-12 15:18:56,789","level":"INFO","thread":"main","message":"test message"}
+
+
+ An event with an error will contain data similar to that below (which has been reformatted to be multi-line).
+
+
+ {
+ "name":"testException",
+ "time":1318429136789,
+ "date":"2011-10-12 15:18:56,789",
+ "level":"INFO",
+ "thread":"quoted\"",
+ "message":"new line\n and {}",
+ "exceptionclass":"java.net.NoRouteToHostException",
+ "stack":[
+ "java.net.NoRouteToHostException: that box caught fire 3 years ago",
+ "\tat org.apache.hadoop.log.TestLog4Json.testException(TestLog4Json.java:49)",
+ "\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)",
+ "\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)",
+ "\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)",
+ "\tat java.lang.reflect.Method.invoke(Method.java:597)",
+ "\tat junit.framework.TestCase.runTest(TestCase.java:168)",
+ "\tat junit.framework.TestCase.runBare(TestCase.java:134)",
+ "\tat junit.framework.TestResult$1.protect(TestResult.java:110)",
+ "\tat junit.framework.TestResult.runProtected(TestResult.java:128)",
+ "\tat junit.framework.TestResult.run(TestResult.java:113)",
+ "\tat junit.framework.TestCase.run(TestCase.java:124)",
+ "\tat junit.framework.TestSuite.runTest(TestSuite.java:232)",
+ "\tat junit.framework.TestSuite.run(TestSuite.java:227)",
+ "\tat org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83)",
+ "\tat org.apache.maven.surefire.junit4.JUnit4TestSet.execute(JUnit4TestSet.java:59)",
+ "\tat org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.executeTestSet(AbstractDirectoryTestSuite.java:120)",
+ "\tat org.apache.maven.surefire.suite.AbstractDirectoryTestSuite.execute(AbstractDirectoryTestSuite.java:145)",
+ "\tat org.apache.maven.surefire.Surefire.run(Surefire.java:104)",
+ "\tat sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)",
+ "\tat sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)",
+ "\tat sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)",
+ "\tat java.lang.reflect.Method.invoke(Method.java:597)",
+ "\tat org.apache.maven.surefire.booter.SurefireBooter.runSuitesInProcess(SurefireBooter.java:290)",
+ "\tat org.apache.maven.surefire.booter.SurefireBooter.main(SurefireBooter.java:1017)"
+ ]
+ }
+ ]]>
+ org.apache.hadoop.metrics.spiorg.apache.hadoop.metrics.fileorg.apache.hadoop.metrics.ganglia
+ private ContextFactory contextFactory = ContextFactory.getFactory();
+
+ void reportMyMetric(float myMetric) {
+ MetricsContext myContext = contextFactory.getContext("myContext");
+ MetricsRecord myRecord = myContext.getRecord("myRecord");
+ myRecord.setMetric("myMetric", myMetric);
+ myRecord.update();
+ }
+
+
+In this example there are three names:
+
+ private MetricsRecord diskStats =
+ contextFactory.getContext("myContext").getRecord("diskStats");
+
+ void reportDiskMetrics(String diskName, float diskBusy, float diskUsed) {
+ diskStats.setTag("diskName", diskName);
+ diskStats.setMetric("diskBusy", diskBusy);
+ diskStats.setMetric("diskUsed", diskUsed);
+ diskStats.update();
+ }
+
+
+MetricsRecord.update() is called. Instead it is stored in an
+internal table, and the contents of the table are sent periodically.
+This can be important for two reasons:
+registerUpdater() method. The benefit of this
+versus using java.util.Timer is that the callbacks will be done
+immediately before sending the data, making the data as current as possible.
+
+
+ ContextFactory factory = ContextFactory.getFactory();
+ ... examine and/or modify factory attributes ...
+ MetricsContext context = factory.getContext("myContext");
+
+The factory attributes can be examined and modified using the following
+ContextFactorymethods:
+Object getAttribute(String attributeName)String[] getAttributeNames()void setAttribute(String name, Object value)void removeAttribute(attributeName)ContextFactory.getFactory() initializes the factory attributes by
+reading the properties file hadoop-metrics.properties if it exists
+on the class path.
+
+
+A factory attribute named:
++contextName.class ++should have as its value the fully qualified name of the class to be +instantiated by a call of the
CodeFactory method
+getContext(contextName). If this factory attribute is not
+specified, the default is to instantiate
+org.apache.hadoop.metrics.file.FileContext.
+
+
+Other factory attributes are specific to a particular implementation of this
+API and are documented elsewhere. For example, configuration attributes for
+the file and Ganglia implementations can be found in the javadoc for
+their respective packages.]]>
+ + myContextName.fileName=/tmp/metrics.log + myContextName.period=5 ++ @see org.apache.hadoop.metrics2.sink.FileSink for metrics 2.0.]]> +
recordName is not in that set.
+
+ @param recordName the name of the record
+ @throws MetricsException if recordName conflicts with configuration data]]>
+ emitRecord method in order to transmit
+ the data. ]]>
+ remove().]]>
+ org.apache.hadoop.metrics.ganglia.
+
+Plugging in an implementation involves writing a concrete subclass of
+AbstractMetricsContext. The subclass should get its
+ configuration information using the getAttribute(attributeName)
+ method.]]>
+ Configured
+ base class, and should not be changed to do so, as it causes problems
+ for subclasses. The constructor of the Configured calls
+ the {@link #setConf(Configuration)} method, which will call into the
+ subclasses before they have been fully constructed.]]>
+ RawScriptBasedMapping that performs
+ the work: reading the configuration parameters, executing any defined
+ script, handling errors and such like. The outer
+ class extends {@link CachedDNSToSwitchMapping} to cache the delegated
+ queries.
+
+ This DNS mapper's {@link #isSingleSwitch()} predicate returns
+ true if and only if a script is defined.]]>
+ + This class uses the configuration parameter {@code + net.topology.table.file.name} to locate the mapping file. +
++ Calls to {@link #resolve(List)} will look up the address as defined in the + mapping file. If no entry corresponding to the address is found, the value + {@code /default-rack} is returned. +
]]> ++ DEPRECATED: Replaced by Avro. +
+ +
+recfile = *include module *record
+include = "include" path
+path = (relative-path / absolute-path)
+module = "module" module-name
+module-name = name *("." name)
+record := "class" name "{" 1*(field) "}"
+field := type name ";"
+name := ALPHA (ALPHA / DIGIT / "_" )*
+type := (ptype / ctype)
+ptype := ("byte" / "boolean" / "int" |
+ "long" / "float" / "double"
+ "ustring" / "buffer")
+ctype := (("vector" "<" type ">") /
+ ("map" "<" type "," type ">" ) ) / name)
+
+module links {
+ class Link {
+ ustring URL;
+ boolean isRelative;
+ ustring anchorText;
+ };
+}
+
+include "links.jr"
+
+module outlinks {
+ class OutLinks {
+ ustring baseURL;
+ vector outLinks;
+ };
+}
+
+$ rcc -l C++ ...
+
+namespace hadoop {
+
+ enum RecFormat { kBinary, kXML, kCSV };
+
+ class InStream {
+ public:
+ virtual ssize_t read(void *buf, size_t n) = 0;
+ };
+
+ class OutStream {
+ public:
+ virtual ssize_t write(const void *buf, size_t n) = 0;
+ };
+
+ class IOError : public runtime_error {
+ public:
+ explicit IOError(const std::string& msg);
+ };
+
+ class IArchive;
+ class OArchive;
+
+ class RecordReader {
+ public:
+ RecordReader(InStream& in, RecFormat fmt);
+ virtual ~RecordReader(void);
+
+ virtual void read(Record& rec);
+ };
+
+ class RecordWriter {
+ public:
+ RecordWriter(OutStream& out, RecFormat fmt);
+ virtual ~RecordWriter(void);
+
+ virtual void write(Record& rec);
+ };
+
+
+ class Record {
+ public:
+ virtual std::string type(void) const = 0;
+ virtual std::string signature(void) const = 0;
+ protected:
+ virtual bool validate(void) const = 0;
+
+ virtual void
+ serialize(OArchive& oa, const std::string& tag) const = 0;
+
+ virtual void
+ deserialize(IArchive& ia, const std::string& tag) = 0;
+ };
+}
+
+namespace links {
+ class Link : public hadoop::Record {
+ // ....
+ };
+};
+
+...
+private:
+ int32_t mMyField;
+ ...
+public:
+ int32_t getMyField(void) const {
+ return mMyField;
+ };
+
+ void setMyField(int32_t m) {
+ mMyField = m;
+ };
+ ...
+
+...
+private:
+ std::string mMyBuf;
+ ...
+public:
+
+ std::string& getMyBuf() {
+ return mMyBuf;
+ };
+
+ const std::string& getMyBuf() const {
+ return mMyBuf;
+ };
+ ...
+
+module inclrec {
+ class RI {
+ int I32;
+ double D;
+ ustring S;
+ };
+}
+
+include "inclrec.jr"
+module testrec {
+ class R {
+ vector VF;
+ RI Rec;
+ buffer Buf;
+ };
+}
+
+$ rcc -l c++ inclrec.jr testrec.jr
+
+#ifndef _INCLREC_JR_HH_
+#define _INCLREC_JR_HH_
+
+#include "recordio.hh"
+
+namespace inclrec {
+
+ class RI : public hadoop::Record {
+
+ private:
+
+ int32_t I32;
+ double D;
+ std::string S;
+
+ public:
+
+ RI(void);
+ virtual ~RI(void);
+
+ virtual bool operator==(const RI& peer) const;
+ virtual bool operator<(const RI& peer) const;
+
+ virtual int32_t getI32(void) const { return I32; }
+ virtual void setI32(int32_t v) { I32 = v; }
+
+ virtual double getD(void) const { return D; }
+ virtual void setD(double v) { D = v; }
+
+ virtual std::string& getS(void) const { return S; }
+ virtual const std::string& getS(void) const { return S; }
+
+ virtual std::string type(void) const;
+ virtual std::string signature(void) const;
+
+ protected:
+
+ virtual void serialize(hadoop::OArchive& a) const;
+ virtual void deserialize(hadoop::IArchive& a);
+ };
+} // end namespace inclrec
+
+#endif /* _INCLREC_JR_HH_ */
+
+
+
+#ifndef _TESTREC_JR_HH_
+#define _TESTREC_JR_HH_
+
+#include "inclrec.jr.hh"
+
+namespace testrec {
+ class R : public hadoop::Record {
+
+ private:
+
+ std::vector VF;
+ inclrec::RI Rec;
+ std::string Buf;
+
+ public:
+
+ R(void);
+ virtual ~R(void);
+
+ virtual bool operator==(const R& peer) const;
+ virtual bool operator<(const R& peer) const;
+
+ virtual std::vector& getVF(void) const;
+ virtual const std::vector& getVF(void) const;
+
+ virtual std::string& getBuf(void) const ;
+ virtual const std::string& getBuf(void) const;
+
+ virtual inclrec::RI& getRec(void) const;
+ virtual const inclrec::RI& getRec(void) const;
+
+ virtual bool serialize(hadoop::OutArchive& a) const;
+ virtual bool deserialize(hadoop::InArchive& a);
+
+ virtual std::string type(void) const;
+ virtual std::string signature(void) const;
+ };
+}; // end namespace testrec
+#endif /* _TESTREC_JR_HH_ */
+
+
+DDL Type C++ Type Java Type
+
+boolean bool boolean
+byte int8_t byte
+int int32_t int
+long int64_t long
+float float float
+double double double
+ustring std::string java.lang.String
+buffer std::string org.apache.hadoop.record.Buffer
+class type class type class type
+vector std::vector java.util.ArrayList
+map std::map java.util.TreeMap
+
+record = primitive / struct / vector / map
+primitive = boolean / int / long / float / double / ustring / buffer
+
+boolean = "T" / "F"
+int = ["-"] 1*DIGIT
+long = ";" ["-"] 1*DIGIT
+float = ["-"] 1*DIGIT "." 1*DIGIT ["E" / "e" ["-"] 1*DIGIT]
+double = ";" ["-"] 1*DIGIT "." 1*DIGIT ["E" / "e" ["-"] 1*DIGIT]
+
+ustring = "'" *(UTF8 char except NULL, LF, % and , / "%00" / "%0a" / "%25" / "%2c" )
+
+buffer = "#" *(BYTE except NULL, LF, % and , / "%00" / "%0a" / "%25" / "%2c" )
+
+struct = "s{" record *("," record) "}"
+vector = "v{" [record *("," record)] "}"
+map = "m{" [*(record "," record)] "}"
+
+class {
+ int MY_INT; // value 5
+ vector MY_VEC; // values 0.1, -0.89, 2.45e4
+ buffer MY_BUF; // value '\00\n\tabc%'
+}
+
+<value>
+ <struct>
+ <member>
+ <name>MY_INT</name>
+ <value><i4>5</i4></value>
+ </member>
+ <member>
+ <name>MY_VEC</name>
+ <value>
+ <array>
+ <data>
+ <value><ex:float>0.1</ex:float></value>
+ <value><ex:float>-0.89</ex:float></value>
+ <value><ex:float>2.45e4</ex:float></value>
+ </data>
+ </array>
+ </value>
+ </member>
+ <member>
+ <name>MY_BUF</name>
+ <value><string>%00\n\tabc%25</string></value>
+ </member>
+ </struct>
+</value>
++ DEPRECATED: Replaced by Avro. +
]]> + The task requires the file or the nested fileset element to be
+ specified. Optional attributes are language (set the output
+ language, default is "java"),
+ destdir (name of the destination directory for generated java/c++
+ code, default is ".") and failonerror (specifies error handling
+ behavior. default is true).
+
+ <recordcc
+ destdir="${basedir}/gensrc"
+ language="java">
+ <fileset include="**\/*.jr" />
+ </recordcc>
+
+
+ @deprecated Replaced by Avro.]]>
+ + DEPRECATED: Replaced by Avro. +
]]> +core-default.xml file, after the comment
+ 'HTTP Authentication' for details on the configuration options.
+ All related configuration properties have 'hadoop.http.authentication.'
+ as prefix.]]>
+ null the default one will be used.]]>
+ null the default one will be used.
+ @param connConfigurator a connection configurator.]]>
+ TRUE if the token is transmitted in the
+ URL query string, FALSE if the delegation token is transmitted
+ using the {@link DelegationTokenAuthenticator#DELEGATION_TOKEN_HEADER} HTTP
+ header.]]>
+ FALSE if the delegation token is transmitted using the
+ {@link DelegationTokenAuthenticator#DELEGATION_TOKEN_HEADER} HTTP header.]]>
+ doAs parameter is not NULL,
+ the request will be done on behalf of the specified doAs user.
+
+ @param url the URL to connect to. Only HTTP/S URLs are supported.
+ @param token the authentication token being used for the user.
+ @param doAs user to do the the request on behalf of, if NULL the request is
+ as self.
+ @return an authenticated {@link HttpURLConnection}.
+ @throws IOException if an IO error occurred.
+ @throws AuthenticationException if an authentication exception occurred.]]>
+ AuthenticatedURL instances are not thread-safe.]]>
+ -' (dash) and '.' (dot) separators,1.0alpha1 => [1, 0, alpha, 1]alpha or abeta or bmilestone or mrc or crsnapshot(the empty string) or ga or finalspProgressable
+ to explicitly report progress to the Hadoop framework. This is especially
+ important for operations which take significant amount of time since,
+ in-lieu of the reported progress, the framework has to assume that an error
+ has occured and time-out the operation.]]>
+ Class of the given object.]]>
+ ShutdownHookManager singleton.]]>
+ Tool, is the standard for any Map-Reduce tool/application.
+ The tool/application should delegate the handling of
+
+ standard command-line options to {@link ToolRunner#run(Tool, String[])}
+ and only handle its custom arguments.
+
+ Here is how a typical Tool is implemented:
+ public class MyApp extends Configured implements Tool {
+
+ public int run(String[] args) throws Exception {
+ // Configuration processed by ToolRunner
+ Configuration conf = getConf();
+
+ // Create a JobConf using the processed conf
+ JobConf job = new JobConf(conf, MyApp.class);
+
+ // Process custom command-line options
+ Path in = new Path(args[1]);
+ Path out = new Path(args[2]);
+
+ // Specify various job-specific parameters
+ job.setJobName("my-app");
+ job.setInputPath(in);
+ job.setOutputPath(out);
+ job.setMapperClass(MyMapper.class);
+ job.setReducerClass(MyReducer.class);
+
+ // Submit the job, then poll for progress until the job is complete
+ JobClient.runJob(job);
+ return 0;
+ }
+
+ public static void main(String[] args) throws Exception {
+ // Let ToolRunner handle generic command-line options
+ int res = ToolRunner.run(new Configuration(), new MyApp(), args);
+
+ System.exit(res);
+ }
+ }
+ Configuration, or builds one if null.
+
+ Sets the Tool's configuration with the possibly modified
+ version of the conf.
+
+ @param conf Configuration for the Tool.
+ @param tool Tool to run.
+ @param args command-line arguments to the tool.
+ @return exit code of the {@link Tool#run(String[])} method.]]>
+ Configuration.
+
+ Equivalent to run(tool.getConf(), tool, args).
+
+ @param tool Tool to run.
+ @param args command-line arguments to the tool.
+ @return exit code of the {@link Tool#run(String[])} method.]]>
+ ToolRunner can be used to run classes implementing
+ Tool interface. It works in conjunction with
+ {@link GenericOptionsParser} to parse the
+
+ generic hadoop command line arguments and modifies the
+ Configuration of the Tool. The
+ application-specific options are passed along without being modified.
+
+
+ @see Tool
+ @see GenericOptionsParser]]>
+ + The Bloom filter is a data structure that was introduced in 1970 and that has been adopted by + the networking research community in the past decade thanks to the bandwidth efficiencies that it + offers for the transmission of set membership information between networked hosts. A sender encodes + the information into a bit vector, the Bloom filter, that is more compact than a conventional + representation. Computation and space costs for construction are linear in the number of elements. + The receiver uses the filter to test whether various elements are members of the set. Though the + filter will occasionally return a false positive, it will never return a false negative. When creating + the filter, the sender can choose its desired point in a trade-off between the false positive rate and the size. + +
+ Originally created by + European Commission One-Lab Project 034819. + + @see Filter The general behavior of a filter + + @see Space/Time Trade-Offs in Hash Coding with Allowable Errors]]> +
+ Invariant: nothing happens if the specified key does not belong to this counter Bloom filter. + @param key The key to remove.]]> +
NOTE: due to the bucket size of this filter, inserting the same
+ key more than 15 times will cause an overflow at all filter positions
+ associated with this key, and it will significantly increase the error
+ rate for this and other keys. For this reason the filter can only be
+ used to store small count values 0 <= N << 15.
+ @param key key to be tested
+ @return 0 if the key is not present. Otherwise, a positive value v will
+ be returned such that v == count with probability equal to the
+ error rate of this filter, and v > count otherwise.
+ Additionally, if the filter experienced an underflow as a result of
+ {@link #delete(Key)} operation, the return value may be lower than the
+ count with the probability of the false negative rate of such
+ filter.]]>
+
+ A counting Bloom filter is an improvement to standard a Bloom filter as it + allows dynamic additions and deletions of set membership information. This + is achieved through the use of a counting vector instead of a bit vector. +
+ Originally created by + European Commission One-Lab Project 034819. + + @see Filter The general behavior of a filter + + @see Summary cache: a scalable wide-area web cache sharing protocol]]> +
+ A dynamic Bloom filter (DBF) makes use of a s * m bit matrix but
+ each of the s rows is a standard Bloom filter. The creation
+ process of a DBF is iterative. At the start, the DBF is a 1 * m
+ bit matrix, i.e., it is composed of a single standard Bloom filter.
+ It assumes that nr elements are recorded in the
+ initial bit vector, where nr <= n (n is
+ the cardinality of the set A to record in the filter).
+
+ As the size of A grows during the execution of the application,
+ several keys must be inserted in the DBF. When inserting a key into the DBF,
+ one must first get an active Bloom filter in the matrix. A Bloom filter is
+ active when the number of recorded keys, nr, is
+ strictly less than the current cardinality of A, n.
+ If an active Bloom filter is found, the key is inserted and
+ nr is incremented by one. On the other hand, if there
+ is no active Bloom filter, a new one is created (i.e., a new row is added to
+ the matrix) according to the current size of A and the element
+ is added in this new Bloom filter and the nr value of
+ this new Bloom filter is set to one. A given key is said to belong to the
+ DBF if the k positions are set to one in one of the matrix rows.
+
+ Originally created by + European Commission One-Lab Project 034819. + + @see Filter The general behavior of a filter + @see BloomFilter A Bloom filter + + @see Theory and Network Applications of Dynamic Bloom Filters]]> +
+ Invariant: if the false positive is null, nothing happens.
+ @param key The false positive key to add.]]>
+
+ It allows the removal of selected false positives at the cost of introducing + random false negatives, and with the benefit of eliminating some random false + positives at the same time. + +
+ Originally created by + European Commission One-Lab Project 034819. + + @see Filter The general behavior of a filter + @see BloomFilter A Bloom filter + @see RemoveScheme The different selective clearing algorithms + + @see Retouched Bloom Filters: Allowing Networked Applications to Trade Off Selected False Positives Against False Negatives]]> +
The most important difference is that unlike GFS, Hadoop DFS files +have strictly one writer at any one time. Bytes are always appended +to the end of the writer's stream. There is no notion of "record appends" +or "mutations" that are then checked or reordered. Writers simply emit +a byte stream. That byte stream is guaranteed to be stored in the +order written.
]]> ++ During name node startup {@link SafeModeInfo} counts the number of + safe blocks, those that have at least the minimal number of + replicas, and calculates the ratio of safe blocks to the total number + of blocks in the system, which is the size of blocks in + {@link FSNamesystem#blockManager}. When the ratio reaches the + {@link #threshold} it starts the SafeModeMonitor daemon in order + to monitor whether the safe mode {@link #extension} is passed. + Then it leaves safe mode and destroys itself. +
+ If safe mode is turned on manually then the number of safe blocks is + not tracked because the name node is not intended to leave safe mode + automatically in the case. + + @see ClientProtocol#setSafeMode(HdfsConstants.SafeModeAction, boolean)]]> +
webhdfs]]>
+