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hdfs-default.xml
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hdfs-default.xml
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			<?xml version="1.0"?>
			<?xml-stylesheet type="text/xsl" href="configuration.xsl"?>

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			<configuration>

			<property>
			<name>hadoop.hdfs.configuration.version</name>
			<value>1</value>
			<description>version of this configuration file</description>
			</property>

			<property>
			<name>dfs.namenode.logging.level</name>
			<value>info</value>
			<description>
			The logging level for dfs namenode. Other values are "dir" (trace
			namespace mutations), "block" (trace block under/over replications
			and block creations/deletions), or "all".
			</description>
			</property>

			<property>
			<name>dfs.namenode.rpc-address</name>
			<value></value>
			<description>
			RPC address that handles all clients requests. In the case of HA/Federation where multiple namenodes exist,
			the name service id is added to the name e.g. dfs.namenode.rpc-address.ns1
			dfs.namenode.rpc-address.EXAMPLENAMESERVICE
			The value of this property will take the form of nn-host1:rpc-port.
			</description>
			</property>

			<property>
			<name>dfs.namenode.rpc-bind-host</name>
			<value></value>
			<description>
			The actual address the server will bind to. If this optional address is
			set, the RPC server will bind to this address and the port specified in
			dfs.namenode.rpc-address for the RPC server. It can also be specified
			per name node or name service for HA/Federation. This is most useful for
			making name node listen to all interfaces by setting to 0.0.0.0.
			</description>
			</property>

			<property>
			<name>dfs.namenode.servicerpc-address</name>
			<value></value>
			<description>
			RPC address for HDFS Services communication. BackupNode, Datanodes and all other services should be
			connecting to this address if it is configured. In the case of HA/Federation where multiple namenodes exist,
			the name service id is added to the name e.g. dfs.namenode.servicerpc-address.ns1
			dfs.namenode.rpc-address.EXAMPLENAMESERVICE
			The value of this property will take the form of nn-host1:rpc-port.
			If the value of this property is unset the value of dfs.namenode.rpc-address will be used as the default.
			</description>
			</property>

			<property>
			<name>dfs.namenode.servicerpc-bind-host</name>
			<value></value>
			<description>
			The actual address the server will bind to. If this optional address is
			set, the service RPC server will bind to this address and the port
			specified in dfs.namenode.servicerpc-address. It can also be specified
			per name node or name service for HA/Federation. This is most useful for
			making name node listen to all interfaces by setting to 0.0.0.0.
			</description>
			</property>

			<property>
			<name>dfs.namenode.secondary.http-address</name>
			<value>0.0.0.0:50090</value>
			<description>
			The secondary namenode http server address and port.
			</description>
			</property>

			<property>
			<name>dfs.datanode.address</name>
			<value>0.0.0.0:50010</value>
			<description>
			The datanode server address and port for data transfer.
			</description>
			</property>

			<property>
			<name>dfs.datanode.http.address</name>
			<value>0.0.0.0:50075</value>
			<description>
			The datanode http server address and port.
			</description>
			</property>

			<property>
			<name>dfs.datanode.ipc.address</name>
			<value>0.0.0.0:50020</value>
			<description>
			The datanode ipc server address and port.
			</description>
			</property>

			<property>
			<name>dfs.datanode.handler.count</name>
			<value>10</value>
			<description>The number of server threads for the datanode.</description>
			</property>

			<property>
			<name>dfs.namenode.http-address</name>
			<value>0.0.0.0:50070</value>
			<description>
			The address and the base port where the dfs namenode web ui will listen on.
			</description>
			</property>

			<property>
			<name>dfs.https.enable</name>
			<value>false</value>
			<description>
			Deprecated. Use "dfs.http.policy" instead.
			</description>
			</property>

			<property>
			<name>dfs.http.policy</name>
			<value>HTTP_ONLY</value>
			<description>Decide if HTTPS(SSL) is supported on HDFS
			This configures the HTTP endpoint for HDFS daemons:
			The following values are supported:
			- HTTP_ONLY : Service is provided only on http
			- HTTPS_ONLY : Service is provided only on https
			- HTTP_AND_HTTPS : Service is provided both on http and https
			</description>
			</property>

			<property>
			<name>dfs.client.https.need-auth</name>
			<value>false</value>
			<description>Whether SSL client certificate authentication is required
			</description>
			</property>

			<property>
			<name>dfs.https.server.keystore.resource</name>
			<value>ssl-server.xml</value>
			<description>Resource file from which ssl server keystore
			information will be extracted
			</description>
			</property>

			<property>
			<name>dfs.client.https.keystore.resource</name>
			<value>ssl-client.xml</value>
			<description>Resource file from which ssl client keystore
			information will be extracted
			</description>
			</property>

			<property>
			<name>dfs.datanode.https.address</name>
			<value>0.0.0.0:50475</value>
			<description>The datanode secure http server address and port.</description>
			</property>

			<property>
			<name>dfs.namenode.https-address</name>
			<value>0.0.0.0:50470</value>
			<description>The namenode secure http server address and port.</description>
			</property>

			<property>
			<name>dfs.datanode.dns.interface</name>
			<value>default</value>
			<description>The name of the Network Interface from which a data node should
			report its IP address.
			</description>
			</property>

			<property>
			<name>dfs.datanode.dns.nameserver</name>
			<value>default</value>
			<description>The host name or IP address of the name server (DNS)
			which a DataNode should use to determine the host name used by the
			NameNode for communication and display purposes.
			</description>
			</property>

			<property>
			<name>dfs.namenode.backup.address</name>
			<value>0.0.0.0:50100</value>
			<description>
			The backup node server address and port.
			If the port is 0 then the server will start on a free port.
			</description>
			</property>

			<property>
			<name>dfs.namenode.backup.http-address</name>
			<value>0.0.0.0:50105</value>
			<description>
			The backup node http server address and port.
			If the port is 0 then the server will start on a free port.
			</description>
			</property>

			<property>
			<name>dfs.namenode.replication.considerLoad</name>
			<value>true</value>
			<description>Decide if chooseTarget considers the target's load or not
			</description>
			</property>
			<property>
			<name>dfs.default.chunk.view.size</name>
			<value>32768</value>
			<description>The number of bytes to view for a file on the browser.
			</description>
			</property>

			<property>
			<name>dfs.datanode.du.reserved</name>
			<value>0</value>
			<description>Reserved space in bytes per volume. Always leave this much space free for non dfs use.
			</description>
			</property>

			<property>
			<name>dfs.namenode.name.dir</name>
			<value>file://${hadoop.tmp.dir}/dfs/name</value>
			<description>Determines where on the local filesystem the DFS name node
			should store the name table(fsimage). If this is a comma-delimited list
			of directories then the name table is replicated in all of the
			directories, for redundancy. </description>
			</property>

			<property>
			<name>dfs.namenode.name.dir.restore</name>
			<value>false</value>
			<description>Set to true to enable NameNode to attempt recovering a
			previously failed dfs.namenode.name.dir. When enabled, a recovery of any
			failed directory is attempted during checkpoint.</description>
			</property>

			<property>
			<name>dfs.namenode.fs-limits.max-component-length</name>
			<value>0</value>
			<description>Defines the maximum number of characters in each component
			of a path. A value of 0 will disable the check.</description>
			</property>

			<property>
			<name>dfs.namenode.fs-limits.max-directory-items</name>
			<value>0</value>
			<description>Defines the maximum number of items that a directory may
			contain. A value of 0 will disable the check.</description>
			</property>

			<property>
			<name>dfs.namenode.fs-limits.min-block-size</name>
			<value>1048576</value>
			<description>Minimum block size in bytes, enforced by the Namenode at create
			time. This prevents the accidental creation of files with tiny block
			sizes (and thus many blocks), which can degrade
			performance.</description>
			</property>

			<property>
			<name>dfs.namenode.fs-limits.max-blocks-per-file</name>
			<value>1048576</value>
			<description>Maximum number of blocks per file, enforced by the Namenode on
			write. This prevents the creation of extremely large files which can
			degrade performance.</description>
			</property>

			<property>
			<name>dfs.namenode.edits.dir</name>
			<value>${dfs.namenode.name.dir}</value>
			<description>Determines where on the local filesystem the DFS name node
			should store the transaction (edits) file. If this is a comma-delimited list
			of directories then the transaction file is replicated in all of the
			directories, for redundancy. Default value is same as dfs.namenode.name.dir
			</description>
			</property>

			<property>
			<name>dfs.namenode.shared.edits.dir</name>
			<value></value>
			<description>A directory on shared storage between the multiple namenodes
			in an HA cluster. This directory will be written by the active and read
			by the standby in order to keep the namespaces synchronized. This directory
			does not need to be listed in dfs.namenode.edits.dir above. It should be
			left empty in a non-HA cluster.
			</description>
			</property>

			<property>
			<name>dfs.namenode.edits.journal-plugin.qjournal</name>
			<value>org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager</value>
			</property>

			<property>
			<name>dfs.permissions.enabled</name>
			<value>true</value>
			<description>
			If "true", enable permission checking in HDFS.
			If "false", permission checking is turned off,
			but all other behavior is unchanged.
			Switching from one parameter value to the other does not change the mode,
			owner or group of files or directories.
			</description>
			</property>

			<property>
			<name>dfs.permissions.superusergroup</name>
			<value>supergroup</value>
			<description>The name of the group of super-users.</description>
			</property>
			<!--
			<property>
			<name>dfs.cluster.administrators</name>
			<value>ACL for the admins</value>
			<description>This configuration is used to control who can access the
			default servlets in the namenode, etc.
			</description>
			</property>
			-->

			<property>
			<name>dfs.block.access.token.enable</name>
			<value>false</value>
			<description>
			If "true", access tokens are used as capabilities for accessing datanodes.
			If "false", no access tokens are checked on accessing datanodes.
			</description>
			</property>

			<property>
			<name>dfs.block.access.key.update.interval</name>
			<value>600</value>
			<description>
			Interval in minutes at which namenode updates its access keys.
			</description>
			</property>

			<property>
			<name>dfs.block.access.token.lifetime</name>
			<value>600</value>
			<description>The lifetime of access tokens in minutes.</description>
			</property>

			<property>
			<name>dfs.datanode.data.dir</name>
			<value>file://${hadoop.tmp.dir}/dfs/data</value>
			<description>Determines where on the local filesystem an DFS data node
			should store its blocks. If this is a comma-delimited
			list of directories, then data will be stored in all named
			directories, typically on different devices.
			Directories that do not exist are ignored.
			</description>
			</property>

			<property>
			<name>dfs.datanode.data.dir.perm</name>
			<value>700</value>
			<description>Permissions for the directories on on the local filesystem where
			the DFS data node store its blocks. The permissions can either be octal or
			symbolic.</description>
			</property>

			<property>
			<name>dfs.replication</name>
			<value>3</value>
			<description>Default block replication.
			The actual number of replications can be specified when the file is created.
			The default is used if replication is not specified in create time.
			</description>
			</property>

			<property>
			<name>dfs.replication.max</name>
			<value>512</value>
			<description>Maximal block replication.
			</description>
			</property>

			<property>
			<name>dfs.namenode.replication.min</name>
			<value>1</value>
			<description>Minimal block replication.
			</description>
			</property>

			<property>
			<name>dfs.blocksize</name>
			<value>134217728</value>
			<description>
			The default block size for new files, in bytes.
			You can use the following suffix (case insensitive):
			k(kilo), m(mega), g(giga), t(tera), p(peta), e(exa) to specify the size (such as 128k, 512m, 1g, etc.),
			Or provide complete size in bytes (such as 134217728 for 128 MB).
			</description>
			</property>

			<property>
			<name>dfs.client.block.write.retries</name>
			<value>3</value>
			<description>The number of retries for writing blocks to the data nodes,
			before we signal failure to the application.
			</description>
			</property>

			<property>
			<name>dfs.client.block.write.replace-datanode-on-failure.enable</name>
			<value>true</value>
			<description>
			If there is a datanode/network failure in the write pipeline,
			DFSClient will try to remove the failed datanode from the pipeline
			and then continue writing with the remaining datanodes. As a result,
			the number of datanodes in the pipeline is decreased. The feature is
			to add new datanodes to the pipeline.

			This is a site-wide property to enable/disable the feature.

			When the cluster size is extremely small, e.g. 3 nodes or less, cluster
			administrators may want to set the policy to NEVER in the default
			configuration file or disable this feature. Otherwise, users may
			experience an unusually high rate of pipeline failures since it is
			impossible to find new datanodes for replacement.

			See also dfs.client.block.write.replace-datanode-on-failure.policy
			</description>
			</property>

			<property>
			<name>dfs.client.block.write.replace-datanode-on-failure.policy</name>
			<value>DEFAULT</value>
			<description>
			This property is used only if the value of
			dfs.client.block.write.replace-datanode-on-failure.enable is true.

			ALWAYS: always add a new datanode when an existing datanode is removed.

			NEVER: never add a new datanode.

			DEFAULT:
			Let r be the replication number.
			Let n be the number of existing datanodes.
			Add a new datanode only if r is greater than or equal to 3 and either
			(1) floor(r/2) is greater than or equal to n; or
			(2) r is greater than n and the block is hflushed/appended.
			</description>
			</property>

			<property>
			<name>dfs.blockreport.intervalMsec</name>
			<value>21600000</value>
			<description>Determines block reporting interval in milliseconds.</description>
			</property>

			<property>
			<name>dfs.blockreport.initialDelay</name> <value>0</value>
			<description>Delay for first block report in seconds.</description>
			</property>

			<property>
			<name>dfs.datanode.directoryscan.interval</name>
			<value>21600</value>
			<description>Interval in seconds for Datanode to scan data directories and
			reconcile the difference between blocks in memory and on the disk.
			</description>
			</property>

			<property>
			<name>dfs.datanode.directoryscan.threads</name>
			<value>1</value>
			<description>How many threads should the threadpool used to compile reports
			for volumes in parallel have.
			</description>
			</property>

			<property>
			<name>dfs.heartbeat.interval</name>
			<value>3</value>
			<description>Determines datanode heartbeat interval in seconds.</description>
			</property>

			<property>
			<name>dfs.namenode.handler.count</name>
			<value>10</value>
			<description>The number of server threads for the namenode.</description>
			</property>

			<property>
			<name>dfs.namenode.safemode.threshold-pct</name>
			<value>0.999f</value>
			<description>
			Specifies the percentage of blocks that should satisfy
			the minimal replication requirement defined by dfs.namenode.replication.min.
			Values less than or equal to 0 mean not to wait for any particular
			percentage of blocks before exiting safemode.
			Values greater than 1 will make safe mode permanent.
			</description>
			</property>

			<property>
			<name>dfs.namenode.safemode.min.datanodes</name>
			<value>0</value>
			<description>
			Specifies the number of datanodes that must be considered alive
			before the name node exits safemode.
			Values less than or equal to 0 mean not to take the number of live
			datanodes into account when deciding whether to remain in safe mode
			during startup.
			Values greater than the number of datanodes in the cluster
			will make safe mode permanent.
			</description>
			</property>

			<property>
			<name>dfs.namenode.safemode.extension</name>
			<value>30000</value>
			<description>
			Determines extension of safe mode in milliseconds
			after the threshold level is reached.
			</description>
			</property>

			<property>
			<name>dfs.datanode.balance.bandwidthPerSec</name>
			<value>1048576</value>
			<description>
			Specifies the maximum amount of bandwidth that each datanode
			can utilize for the balancing purpose in term of
			the number of bytes per second.
			</description>
			</property>

			<property>
			<name>dfs.hosts</name>
			<value></value>
			<description>Names a file that contains a list of hosts that are
			permitted to connect to the namenode. The full pathname of the file
			must be specified. If the value is empty, all hosts are
			permitted.</description>
			</property>

			<property>
			<name>dfs.hosts.exclude</name>
			<value></value>
			<description>Names a file that contains a list of hosts that are
			not permitted to connect to the namenode. The full pathname of the
			file must be specified. If the value is empty, no hosts are
			excluded.</description>
			</property>

			<property>
			<name>dfs.namenode.max.objects</name>
			<value>0</value>
			<description>The maximum number of files, directories and blocks
			dfs supports. A value of zero indicates no limit to the number
			of objects that dfs supports.
			</description>
			</property>

			<property>
			<name>dfs.namenode.datanode.registration.ip-hostname-check</name>
			<value>true</value>
			<description>
			If true (the default), then the namenode requires that a connecting
			datanode's address must be resolved to a hostname. If necessary, a reverse
			DNS lookup is performed. All attempts to register a datanode from an
			unresolvable address are rejected.

			It is recommended that this setting be left on to prevent accidental
			registration of datanodes listed by hostname in the excludes file during a
			DNS outage. Only set this to false in environments where there is no
			infrastructure to support reverse DNS lookup.
			</description>
			</property>

			<property>
			<name>dfs.namenode.decommission.interval</name>
			<value>30</value>
			<description>Namenode periodicity in seconds to check if decommission is
			complete.</description>
			</property>

			<property>
			<name>dfs.namenode.decommission.nodes.per.interval</name>
			<value>5</value>
			<description>The number of nodes namenode checks if decommission is complete
			in each dfs.namenode.decommission.interval.</description>
			</property>

			<property>
			<name>dfs.namenode.replication.interval</name>
			<value>3</value>
			<description>The periodicity in seconds with which the namenode computes
			repliaction work for datanodes. </description>
			</property>

			<property>
			<name>dfs.namenode.accesstime.precision</name>
			<value>3600000</value>
			<description>The access time for HDFS file is precise upto this value.
			The default value is 1 hour. Setting a value of 0 disables
			access times for HDFS.
			</description>
			</property>

			<property>
			<name>dfs.datanode.plugins</name>
			<value></value>
			<description>Comma-separated list of datanode plug-ins to be activated.
			</description>
			</property>

			<property>
			<name>dfs.namenode.plugins</name>
			<value></value>
			<description>Comma-separated list of namenode plug-ins to be activated.
			</description>
			</property>

			<property>
			<name>dfs.stream-buffer-size</name>
			<value>4096</value>
			<description>The size of buffer to stream files.
			The size of this buffer should probably be a multiple of hardware
			page size (4096 on Intel x86), and it determines how much data is
			buffered during read and write operations.</description>
			</property>

			<property>
			<name>dfs.bytes-per-checksum</name>
			<value>512</value>
			<description>The number of bytes per checksum. Must not be larger than
			dfs.stream-buffer-size</description>
			</property>

			<property>
			<name>dfs.client-write-packet-size</name>
			<value>65536</value>
			<description>Packet size for clients to write</description>
			</property>

			<property>
			<name>dfs.client.write.exclude.nodes.cache.expiry.interval.millis</name>
			<value>600000</value>
			<description>The maximum period to keep a DN in the excluded nodes list
			at a client. After this period, in milliseconds, the previously excluded node(s) will
			be removed automatically from the cache and will be considered good for block allocations
			again. Useful to lower or raise in situations where you keep a file open for very long
			periods (such as a Write-Ahead-Log (WAL) file) to make the writer tolerant to cluster maintenance
			restarts. Defaults to 10 minutes.</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.dir</name>
			<value>file://${hadoop.tmp.dir}/dfs/namesecondary</value>
			<description>Determines where on the local filesystem the DFS secondary
			name node should store the temporary images to merge.
			If this is a comma-delimited list of directories then the image is
			replicated in all of the directories for redundancy.
			</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.edits.dir</name>
			<value>${dfs.namenode.checkpoint.dir}</value>
			<description>Determines where on the local filesystem the DFS secondary
			name node should store the temporary edits to merge.
			If this is a comma-delimited list of directoires then teh edits is
			replicated in all of the directoires for redundancy.
			Default value is same as dfs.namenode.checkpoint.dir
			</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.period</name>
			<value>3600</value>
			<description>The number of seconds between two periodic checkpoints.
			</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.txns</name>
			<value>1000000</value>
			<description>The Secondary NameNode or CheckpointNode will create a checkpoint
			of the namespace every 'dfs.namenode.checkpoint.txns' transactions, regardless
			of whether 'dfs.namenode.checkpoint.period' has expired.
			</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.check.period</name>
			<value>60</value>
			<description>The SecondaryNameNode and CheckpointNode will poll the NameNode
			every 'dfs.namenode.checkpoint.check.period' seconds to query the number
			of uncheckpointed transactions.
			</description>
			</property>

			<property>
			<name>dfs.namenode.checkpoint.max-retries</name>
			<value>3</value>
			<description>The SecondaryNameNode retries failed checkpointing. If the
			failure occurs while loading fsimage or replaying edits, the number of
			retries is limited by this variable.
			</description>
			</property>

			<property>
			<name>dfs.namenode.num.checkpoints.retained</name>
			<value>2</value>
			<description>The number of image checkpoint files that will be retained by
			the NameNode and Secondary NameNode in their storage directories. All edit
			logs necessary to recover an up-to-date namespace from the oldest retained
			checkpoint will also be retained.
			</description>
			</property>

			<property>
			<name>dfs.namenode.num.extra.edits.retained</name>
			<value>1000000</value>
			<description>The number of extra transactions which should be retained
			beyond what is minimally necessary for a NN restart. This can be useful for
			audit purposes or for an HA setup where a remote Standby Node may have
			been offline for some time and need to have a longer backlog of retained
			edits in order to start again.
			Typically each edit is on the order of a few hundred bytes, so the default
			of 1 million edits should be on the order of hundreds of MBs or low GBs.

			NOTE: Fewer extra edits may be retained than value specified for this setting
			if doing so would mean that more segments would be retained than the number
			configured by dfs.namenode.max.extra.edits.segments.retained.
			</description>
			</property>

			<property>
			<name>dfs.namenode.max.extra.edits.segments.retained</name>
			<value>10000</value>
			<description>The maximum number of extra edit log segments which should be retained
			beyond what is minimally necessary for a NN restart. When used in conjunction with
			dfs.namenode.num.extra.edits.retained, this configuration property serves to cap
			the number of extra edits files to a reasonable value.
			</description>
			</property>

			<property>
			<name>dfs.namenode.delegation.key.update-interval</name>
			<value>86400000</value>
			<description>The update interval for master key for delegation tokens
			in the namenode in milliseconds.
			</description>
			</property>

			<property>
			<name>dfs.namenode.delegation.token.max-lifetime</name>
			<value>604800000</value>
			<description>The maximum lifetime in milliseconds for which a delegation
			token is valid.
			</description>
			</property>

			<property>
			<name>dfs.namenode.delegation.token.renew-interval</name>
			<value>86400000</value>
			<description>The renewal interval for delegation token in milliseconds.
			</description>
			</property>

			<property>
			<name>dfs.datanode.failed.volumes.tolerated</name>
			<value>0</value>
			<description>The number of volumes that are allowed to
			fail before a datanode stops offering service. By default
			any volume failure will cause a datanode to shutdown.
			</description>
			</property>

			<property>
			<name>dfs.image.compress</name>
			<value>false</value>
			<description>Should the dfs image be compressed?
			</description>
			</property>

			<property>
			<name>dfs.image.compression.codec</name>
			<value>org.apache.hadoop.io.compress.DefaultCodec</value>
			<description>If the dfs image is compressed, how should they be compressed?
			This has to be a codec defined in io.compression.codecs.
			</description>
			</property>

			<property>
			<name>dfs.image.transfer.timeout</name>
			<value>600000</value>
			<description>
			Timeout for image transfer in milliseconds. This timeout and the related
			dfs.image.transfer.bandwidthPerSec parameter should be configured such
			that normal image transfer can complete within the timeout.
			This timeout prevents client hangs when the sender fails during
			image transfer, which is particularly important during checkpointing.
			Note that this timeout applies to the entirety of image transfer, and
			is not a socket timeout.
			</description>
			</property>

			<property>
			<name>dfs.image.transfer.bandwidthPerSec</name>
			<value>0</value>
			<description>
			Maximum bandwidth used for image transfer in bytes per second.
			This can help keep normal namenode operations responsive during
			checkpointing. The maximum bandwidth and timeout in
			dfs.image.transfer.timeout should be set such that normal image
			transfers can complete successfully.
			A default value of 0 indicates that throttling is disabled.
			</description>
			</property>

			<property>
			<name>dfs.namenode.support.allow.format</name>
			<value>true</value>
			<description>Does HDFS namenode allow itself to be formatted?
			You may consider setting this to false for any production
			cluster, to avoid any possibility of formatting a running DFS.
			</description>
			</property>

			<property>
			<name>dfs.datanode.max.transfer.threads</name>
			<value>4096</value>
			<description>
			Specifies the maximum number of threads to use for transferring data
			in and out of the DN.
			</description>
			</property>

			<property>
			<name>dfs.datanode.readahead.bytes</name>
			<value>4193404</value>
			<description>
			While reading block files, if the Hadoop native libraries are available,
			the datanode can use the posix_fadvise system call to explicitly
			page data into the operating system buffer cache ahead of the current
			reader's position. This can improve performance especially when
			disks are highly contended.

			This configuration specifies the number of bytes ahead of the current
			read position which the datanode will attempt to read ahead. This
			feature may be disabled by configuring this property to 0.

			If the native libraries are not available, this configuration has no
			effect.
			</description>
			</property>

			<property>
			<name>dfs.datanode.drop.cache.behind.reads</name>
			<value>false</value>
			<description>
			In some workloads, the data read from HDFS is known to be significantly
			large enough that it is unlikely to be useful to cache it in the
			operating system buffer cache. In this case, the DataNode may be
			configured to automatically purge all data from the buffer cache
			after it is delivered to the client. This behavior is automatically
			disabled for workloads which read only short sections of a block
			(e.g HBase random-IO workloads).

			This may improve performance for some workloads by freeing buffer
			cache spage usage for more cacheable data.

			If the Hadoop native libraries are not available, this configuration
			has no effect.
			</description>
			</property>

			<property>
			<name>dfs.datanode.drop.cache.behind.writes</name>
			<value>false</value>
			<description>
			In some workloads, the data written to HDFS is known to be significantly
			large enough that it is unlikely to be useful to cache it in the
			operating system buffer cache. In this case, the DataNode may be
			configured to automatically purge all data from the buffer cache
			after it is written to disk.

			This may improve performance for some workloads by freeing buffer
			cache spage usage for more cacheable data.

			If the Hadoop native libraries are not available, this configuration
			has no effect.
			</description>
			</property>

			<property>
			<name>dfs.datanode.sync.behind.writes</name>
			<value>false</value>
			<description>
			If this configuration is enabled, the datanode will instruct the
			operating system to enqueue all written data to the disk immediately
			after it is written. This differs from the usual OS policy which
			may wait for up to 30 seconds before triggering writeback.

			This may improve performance for some workloads by smoothing the
			IO profile for data written to disk.

			If the Hadoop native libraries are not available, this configuration
			has no effect.
			</description>
			</property>

			<property>
			<name>dfs.client.failover.max.attempts</name>
			<value>15</value>
			<description>
			Expert only. The number of client failover attempts that should be
			made before the failover is considered failed.
			</description>
			</property>

			<property>
			<name>dfs.client.failover.sleep.base.millis</name>
			<value>500</value>
			<description>
			Expert only. The time to wait, in milliseconds, between failover
			attempts increases exponentially as a function of the number of
			attempts made so far, with a random factor of +/- 50%. This option
			specifies the base value used in the failover calculation. The
			first failover will retry immediately. The 2nd failover attempt
			will delay at least dfs.client.failover.sleep.base.millis
			milliseconds. And so on.
			</description>
			</property>

			<property>
			<name>dfs.client.failover.sleep.max.millis</name>
			<value>15000</value>
			<description>
			Expert only. The time to wait, in milliseconds, between failover
			attempts increases exponentially as a function of the number of
			attempts made so far, with a random factor of +/- 50%. This option
			specifies the maximum value to wait between failovers.
			Specifically, the time between two failover attempts will not
			exceed +/- 50% of dfs.client.failover.sleep.max.millis
			milliseconds.
			</description>
			</property>

			<property>
			<name>dfs.client.failover.connection.retries</name>
			<value>0</value>
			<description>
			Expert only. Indicates the number of retries a failover IPC client
			will make to establish a server connection.
			</description>
			</property>

			<property>
			<name>dfs.client.failover.connection.retries.on.timeouts</name>
			<value>0</value>
			<description>
			Expert only. The number of retry attempts a failover IPC client
			will make on socket timeout when establishing a server connection.
			</description>
			</property>

			<property>
			<name>dfs.nameservices</name>
			<value></value>
			<description>
			Comma-separated list of nameservices.
			</description>
			</property>

			<property>
			<name>dfs.nameservice.id</name>
			<value></value>
			<description>
			The ID of this nameservice. If the nameservice ID is not
			configured or more than one nameservice is configured for
			dfs.nameservices it is determined automatically by
			matching the local node's address with the configured address.
			</description>
			</property>

			<property>
			<name>dfs.ha.namenodes.EXAMPLENAMESERVICE</name>
			<value></value>
			<description>
			The prefix for a given nameservice, contains a comma-separated
			list of namenodes for a given nameservice (eg EXAMPLENAMESERVICE).
			</description>
			</property>

			<property>
			<name>dfs.ha.namenode.id</name>
			<value></value>
			<description>
			The ID of this namenode. If the namenode ID is not configured it
			is determined automatically by matching the local node's address
			with the configured address.
			</description>
			</property>

			<property>
			<name>dfs.ha.log-roll.period</name>
			<value>120</value>
			<description>
			How often, in seconds, the StandbyNode should ask the active to
			roll edit logs. Since the StandbyNode only reads from finalized
			log segments, the StandbyNode will only be as up-to-date as how
			often the logs are rolled. Note that failover triggers a log roll
			so the StandbyNode will be up to date before it becomes active.
			</description>
			</property>

			<property>
			<name>dfs.ha.tail-edits.period</name>
			<value>60</value>
			<description>
			How often, in seconds, the StandbyNode should check for new
			finalized log segments in the shared edits log.
			</description>
			</property>

			<property>
			<name>dfs.ha.automatic-failover.enabled</name>
			<value>false</value>
			<description>
			Whether automatic failover is enabled. See the HDFS High
			Availability documentation for details on automatic HA
			configuration.
			</description>
			</property>

			<property>
			<name>dfs.support.append</name>
			<value>true</value>
			<description>
			Does HDFS allow appends to files?
			</description>
			</property>

			<property>
			<name>dfs.client.use.datanode.hostname</name>
			<value>false</value>
			<description>Whether clients should use datanode hostnames when
			connecting to datanodes.
			</description>
			</property>

			<property>
			<name>dfs.datanode.use.datanode.hostname</name>
			<value>false</value>
			<description>Whether datanodes should use datanode hostnames when
			connecting to other datanodes for data transfer.
			</description>
			</property>

			<property>
			<name>dfs.client.local.interfaces</name>
			<value></value>
			<description>A comma separated list of network interface names to use
			for data transfer between the client and datanodes. When creating
			a connection to read from or write to a datanode, the client
			chooses one of the specified interfaces at random and binds its
			socket to the IP of that interface. Individual names may be
			specified as either an interface name (eg "eth0"), a subinterface
			name (eg "eth0:0"), or an IP address (which may be specified using
			CIDR notation to match a range of IPs).
			</description>
			</property>

			<property>
			<name>dfs.namenode.kerberos.internal.spnego.principal</name>
			<value>${dfs.web.authentication.kerberos.principal}</value>
			</property>

			<property>
			<name>dfs.secondary.namenode.kerberos.internal.spnego.principal</name>
			<value>${dfs.web.authentication.kerberos.principal}</value>
			</property>

			<property>
			<name>dfs.namenode.avoid.read.stale.datanode</name>
			<value>false</value>
			<description>
			Indicate whether or not to avoid reading from "stale" datanodes whose
			heartbeat messages have not been received by the namenode
			for more than a specified time interval. Stale datanodes will be
			moved to the end of the node list returned for reading. See
			dfs.namenode.avoid.write.stale.datanode for a similar setting for writes.
			</description>
			</property>

			<property>
			<name>dfs.namenode.avoid.write.stale.datanode</name>
			<value>false</value>
			<description>
			Indicate whether or not to avoid writing to "stale" datanodes whose
			heartbeat messages have not been received by the namenode
			for more than a specified time interval. Writes will avoid using
			stale datanodes unless more than a configured ratio
			(dfs.namenode.write.stale.datanode.ratio) of datanodes are marked as
			stale. See dfs.namenode.avoid.read.stale.datanode for a similar setting
			for reads.
			</description>
			</property>

			<property>
			<name>dfs.namenode.stale.datanode.interval</name>
			<value>30000</value>
			<description>
			Default time interval for marking a datanode as "stale", i.e., if
			the namenode has not received heartbeat msg from a datanode for
			more than this time interval, the datanode will be marked and treated
			as "stale" by default. The stale interval cannot be too small since
			otherwise this may cause too frequent change of stale states.
			We thus set a minimum stale interval value (the default value is 3 times
			of heartbeat interval) and guarantee that the stale interval cannot be less
			than the minimum value. A stale data node is avoided during lease/block
			recovery. It can be conditionally avoided for reads (see
			dfs.namenode.avoid.read.stale.datanode) and for writes (see
			dfs.namenode.avoid.write.stale.datanode).
			</description>
			</property>

			<property>
			<name>dfs.namenode.write.stale.datanode.ratio</name>
			<value>0.5f</value>
			<description>
			When the ratio of number stale datanodes to total datanodes marked
			is greater than this ratio, stop avoiding writing to stale nodes so
			as to prevent causing hotspots.
			</description>
			</property>

			<property>
			<name>dfs.namenode.invalidate.work.pct.per.iteration</name>
			<value>0.32f</value>
			<description>
			Note: Advanced property. Change with caution.
			This determines the percentage amount of block
			invalidations (deletes) to do over a single DN heartbeat
			deletion command. The final deletion count is determined by applying this
			percentage to the number of live nodes in the system.
			The resultant number is the number of blocks from the deletion list
			chosen for proper invalidation over a single heartbeat of a single DN.
			Value should be a positive, non-zero percentage in float notation (X.Yf),
			with 1.0f meaning 100%.
			</description>
			</property>

			<property>
			<name>dfs.namenode.replication.work.multiplier.per.iteration</name>
			<value>2</value>
			<description>
			Note: Advanced property. Change with caution.
			This determines the total amount of block transfers to begin in
			parallel at a DN, for replication, when such a command list is being
			sent over a DN heartbeat by the NN. The actual number is obtained by
			multiplying this multiplier with the total number of live nodes in the
			cluster. The result number is the number of blocks to begin transfers
			immediately for, per DN heartbeat. This number can be any positive,
			non-zero integer.
			</description>
			</property>

			<property>
			<name>dfs.webhdfs.enabled</name>
			<value>true</value>
			<description>
			Enable WebHDFS (REST API) in Namenodes and Datanodes.
			</description>
			</property>

			<property>
			<name>hadoop.fuse.connection.timeout</name>
			<value>300</value>
			<description>
			The minimum number of seconds that we'll cache libhdfs connection objects
			in fuse_dfs. Lower values will result in lower memory consumption; higher
			values may speed up access by avoiding the overhead of creating new
			connection objects.
			</description>
			</property>

			<property>
			<name>hadoop.fuse.timer.period</name>
			<value>5</value>
			<description>
			The number of seconds between cache expiry checks in fuse_dfs. Lower values
			will result in fuse_dfs noticing changes to Kerberos ticket caches more
			quickly.
			</description>
			</property>

			<property>
			<name>dfs.metrics.percentiles.intervals</name>
			<value></value>
			<description>
			Comma-delimited set of integers denoting the desired rollover intervals
			(in seconds) for percentile latency metrics on the Namenode and Datanode.
			By default, percentile latency metrics are disabled.
			</description>
			</property>

			<property>
			<name>dfs.encrypt.data.transfer</name>
			<value>false</value>
			<description>
			Whether or not actual block data that is read/written from/to HDFS should
			be encrypted on the wire. This only needs to be set on the NN and DNs,
			clients will deduce this automatically.
			</description>
			</property>

			<property>
			<name>dfs.encrypt.data.transfer.algorithm</name>
			<value></value>
			<description>
			This value may be set to either "3des" or "rc4". If nothing is set, then
			the configured JCE default on the system is used (usually 3DES.) It is
			widely believed that 3DES is more cryptographically secure, but RC4 is
			substantially faster.
			</description>
			</property>

			<property>
			<name>dfs.datanode.hdfs-blocks-metadata.enabled</name>
			<value>false</value>
			<description>
			Boolean which enables backend datanode-side support for the experimental DistributedFileSystem#getFileVBlockStorageLocations API.
			</description>
			</property>

			<property>
			<name>dfs.client.file-block-storage-locations.num-threads</name>
			<value>10</value>
			<description>
			Number of threads used for making parallel RPCs in DistributedFileSystem#getFileBlockStorageLocations().
			</description>
			</property>

			<property>
			<name>dfs.client.file-block-storage-locations.timeout</name>
			<value>60</value>
			<description>
			Timeout (in seconds) for the parallel RPCs made in DistributedFileSystem#getFileBlockStorageLocations().
			</description>
			</property>

			<property>
			<name>dfs.journalnode.rpc-address</name>
			<value>0.0.0.0:8485</value>
			<description>
			The JournalNode RPC server address and port.
			</description>
			</property>

			<property>
			<name>dfs.journalnode.http-address</name>
			<value>0.0.0.0:8480</value>
			<description>
			The address and port the JournalNode web UI listens on.
			If the port is 0 then the server will start on a free port.
			</description>
			</property>

			<property>
			<name>dfs.namenode.audit.loggers</name>
			<value>default</value>
			<description>
			List of classes implementing audit loggers that will receive audit events.
			These should be implementations of org.apache.hadoop.hdfs.server.namenode.AuditLogger.
			The special value "default" can be used to reference the default audit
			logger, which uses the configured log system. Installing custom audit loggers
			may affect the performance and stability of the NameNode. Refer to the custom
			logger's documentation for more details.
			</description>
			</property>

			<property>
			<name>dfs.domain.socket.path</name>
			<value></value>
			<description>
			Optional. This is a path to a UNIX domain socket that will be used for
			communication between the DataNode and local HDFS clients.
			If the string "_PORT" is present in this path, it will be replaced by the
			TCP port of the DataNode.
			</description>
			</property>

			<property>
			<name>dfs.datanode.available-space-volume-choosing-policy.balanced-space-threshold</name>
			<value>10737418240</value> <!-- 10 GB -->
			<description>
			Only used when the dfs.datanode.fsdataset.volume.choosing.policy is set to
			org.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy.
			This setting controls how much DN volumes are allowed to differ in terms of
			bytes of free disk space before they are considered imbalanced. If the free
			space of all the volumes are within this range of each other, the volumes
			will be considered balanced and block assignments will be done on a pure
			round robin basis.
			</description>
			</property>

			<property>
			<name>dfs.datanode.available-space-volume-choosing-policy.balanced-space-preference-fraction</name>
			<value>0.75f</value>
			<description>
			Only used when the dfs.datanode.fsdataset.volume.choosing.policy is set to
			org.apache.hadoop.hdfs.server.datanode.fsdataset.AvailableSpaceVolumeChoosingPolicy.
			This setting controls what percentage of new block allocations will be sent
			to volumes with more available disk space than others. This setting should
			be in the range 0.0 - 1.0, though in practice 0.5 - 1.0, since there should
			be no reason to prefer that volumes with less available disk space receive
			more block allocations.
			</description>
			</property>

			<property>
			<name>dfs.namenode.edits.noeditlogchannelflush</name>
			<value>false</value>
			<description>
			Specifies whether to flush edit log file channel. When set, expensive
			FileChannel#force calls are skipped and synchronous disk writes are
			enabled instead by opening the edit log file with RandomAccessFile("rws")
			flags. This can significantly improve the performance of edit log writes
			on the Windows platform.
			Note that the behavior of the "rws" flags is platform and hardware specific
			and might not provide the same level of guarantees as FileChannel#force.
			For example, the write will skip the disk-cache on SAS and SCSI devices
			while it might not on SATA devices. This is an expert level setting,
			change with caution.
			</description>
			</property>

			<property>
			<name>dfs.client.cache.drop.behind.writes</name>
			<value></value>
			<description>
			Just like dfs.datanode.drop.cache.behind.writes, this setting causes the
			page cache to be dropped behind HDFS writes, potentially freeing up more
			memory for other uses. Unlike dfs.datanode.drop.cache.behind.writes, this
			is a client-side setting rather than a setting for the entire datanode.
			If present, this setting will override the DataNode default.

			If the native libraries are not available to the DataNode, this
			configuration has no effect.
			</description>
			</property>

			<property>
			<name>dfs.client.cache.drop.behind.reads</name>
			<value></value>
			<description>
			Just like dfs.datanode.drop.cache.behind.reads, this setting causes the
			page cache to be dropped behind HDFS reads, potentially freeing up more
			memory for other uses. Unlike dfs.datanode.drop.cache.behind.reads, this
			is a client-side setting rather than a setting for the entire datanode. If
			present, this setting will override the DataNode default.

			If the native libraries are not available to the DataNode, this
			configuration has no effect.
			</description>
			</property>

			<property>
			<name>dfs.client.cache.readahead</name>
			<value></value>
			<description>
			When using remote reads, this setting causes the datanode to
			read ahead in the block file using posix_fadvise, potentially decreasing
			I/O wait times. Unlike dfs.datanode.readahead.bytes, this is a client-side
			setting rather than a setting for the entire datanode. If present, this
			setting will override the DataNode default.

			When using local reads, this setting determines how much readahead we do in
			BlockReaderLocal.

			If the native libraries are not available to the DataNode, this
			configuration has no effect.
			</description>
			</property>

			<property>
			<name>dfs.namenode.enable.retrycache</name>
			<value>true</value>
			<description>
			This enables the retry cache on the namenode. Namenode tracks for
			non-idempotent requests the corresponding response. If a client retries the
			request, the response from the retry cache is sent. Such operations
			are tagged with annotation @AtMostOnce in namenode protocols. It is
			recommended that this flag be set to true. Setting it to false, will result
			in clients getting failure responses to retried request. This flag must
			be enabled in HA setup for transparent fail-overs.

			The entries in the cache have expiration time configurable
			using dfs.namenode.retrycache.expirytime.millis.
			</description>
			</property>

			<property>
			<name>dfs.namenode.retrycache.expirytime.millis</name>
			<value>600000</value>
			<description>
			The time for which retry cache entries are retained.
			</description>
			</property>

			<property>
			<name>dfs.namenode.retrycache.heap.percent</name>
			<value>0.03f</value>
			<description>
			This parameter configures the heap size allocated for retry cache
			(excluding the response cached). This corresponds to approximately
			4096 entries for every 64MB of namenode process java heap size.
			Assuming retry cache entry expiration time (configured using
			dfs.namenode.retrycache.expirytime.millis) of 10 minutes, this
			enables retry cache to support 7 operations per second sustained
			for 10 minutes. As the heap size is increased, the operation rate
			linearly increases.
			</description>
			</property>

			<property>
			<name>dfs.client.mmap.cache.size</name>
			<value>1024</value>
			<description>
			When zero-copy reads are used, the DFSClient keeps a cache of recently used
			memory mapped regions. This parameter controls the maximum number of
			entries that we will keep in that cache.

			If this is set to 0, we will not allow mmap.

			The larger this number is, the more file descriptors we will potentially
			use for memory-mapped files. mmaped files also use virtual address space.
			You may need to increase your ulimit virtual address space limits before
			increasing the client mmap cache size.
			</description>
			</property>

			<property>
			<name>dfs.client.mmap.cache.timeout.ms</name>
			<value>900000</value>
			<description>
			The minimum length of time that we will keep an mmap entry in the cache
			between uses. If an entry is in the cache longer than this, and nobody
			uses it, it will be removed by a background thread.
			</description>
			</property>

			<property>
			<name>dfs.namenode.path.based.cache.block.map.allocation.percent</name>
			<value>0.25</value>
			<description>
			The percentage of the Java heap which we will allocate to the cached blocks
			map. The cached blocks map is a hash map which uses chained hashing.
			Smaller maps may be accessed more slowly if the number of cached blocks is
			large; larger maps will consume more memory.
			</description>
			</property>

			<property>
			<name>dfs.datanode.max.locked.memory</name>
			<value>0</value>
			<description>
			The amount of memory in bytes to use for caching of block replicas in
			memory on the datanode. The datanode's maximum locked memory soft ulimit
			(RLIMIT_MEMLOCK) must be set to at least this value, else the datanode
			will abort on startup.

			By default, this parameter is set to 0, which disables in-memory caching.

			If the native libraries are not available to the DataNode, this
			configuration has no effect.
			</description>
			</property>

			<property>
			<name>dfs.namenode.list.cache.directives.num.responses</name>
			<value>100</value>
			<description>
			This value controls the number of cache directives that the NameNode will
			send over the wire in response to a listDirectives RPC.
			</description>
			</property>

			<property>
			<name>dfs.namenode.list.cache.pools.num.responses</name>
			<value>100</value>
			<description>
			This value controls the number of cache pools that the NameNode will
			send over the wire in response to a listPools RPC.
			</description>
			</property>

			<property>
			<name>dfs.namenode.path.based.cache.refresh.interval.ms</name>
			<value>300000</value>
			<description>
			The amount of milliseconds between subsequent path cache rescans. Path
			cache rescans are when we calculate which blocks should be cached, and on
			what datanodes.

			By default, this parameter is set to 300000, which is five minutes.
			</description>
			</property>

			<property>
			<name>dfs.namenode.path.based.cache.retry.interval.ms</name>
			<value>60000</value>
			<description>
			When the NameNode needs to uncache something that is cached, or cache
			something that is not cached, it must direct the DataNodes to do so by
			sending a DNA_CACHE or DNA_UNCACHE command in response to a DataNode
			heartbeat. This parameter controls how frequently the NameNode will
			resend these commands.
			</description>
			</property>

			<property>
			<name>dfs.datanode.fsdatasetcache.max.threads.per.volume</name>
			<value>4</value>
			<description>
			The maximum number of threads per volume to use for caching new data
			on the datanode. These threads consume both I/O and CPU. This can affect
			normal datanode operations.
			</description>
			</property>

			<property>
			<name>dfs.cachereport.intervalMsec</name>
			<value>10000</value>
			<description>
			Determines cache reporting interval in milliseconds. After this amount of
			time, the DataNode sends a full report of its cache state to the NameNode.
			The NameNode uses the cache report to update its map of cached blocks to
			DataNode locations.

			This configuration has no effect if in-memory caching has been disabled by
			setting dfs.datanode.max.locked.memory to 0 (which is the default).

			If the native libraries are not available to the DataNode, this
			configuration has no effect.
			</description>
			</property>

			<property>
			<name>dfs.namenode.edit.log.autoroll.multiplier.threshold</name>
			<value>2.0</value>
			<description>
			Determines when an active namenode will roll its own edit log.
			The actual threshold (in number of edits) is determined by multiplying
			this value by dfs.namenode.checkpoint.txns.

			This prevents extremely large edit files from accumulating on the active
			namenode, which can cause timeouts during namenode startup and pose an
			administrative hassle. This behavior is intended as a failsafe for when
			the standby or secondary namenode fail to roll the edit log by the normal
			checkpoint threshold.
			</description>
			</property>

			<property>
			<name>dfs.namenode.edit.log.autoroll.check.interval.ms</name>
			<value>300000</value>
			<description>
			How often an active namenode will check if it needs to roll its edit log,
			in milliseconds.
			</description>
			</property>

			<property>
			<name>dfs.webhdfs.user.provider.user.pattern</name>
			<value>^[A-Za-z_][A-Za-z0-9._-]*[$]?$</value>
			<description>
			Valid pattern for user and group names for webhdfs, it must be a valid java regex.
			</description>
			</property>

			</configuration>

R3704/2.3.0/hadoop-2.3.0/share/hadoop/hadoop-project-dist/hadoop-hdfs/hdfs-default.xml6c2cef95801e2.3.0_2.4.1

hdfs-default.xmlView Options

R3704/2.3.0/hadoop-2.3.0/share/hadoop/hadoop-project-dist/hadoop-hdfs/hdfs-default.xml
6c2cef95801e2.3.0_2.4.1

hdfs-default.xml
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