hadoop/hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

<?xml version="1.0"?>
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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 RPC server will bind to. If this optional address is
    set, it overrides only the hostname portion of dfs.namenode.rpc-address.
    It can also be specified per name node or name service for HA/Federation.
    This is useful for making the name node listen on all interfaces by
    setting it 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 service RPC server will bind to. If this optional address is
    set, it overrides only the hostname portion of dfs.namenode.servicerpc-address.
    It can also be specified per name node or name service for HA/Federation.
    This is useful for making the name node listen on all interfaces by
    setting it 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.namenode.secondary.https-address</name>
  <value>0.0.0.0:50091</value>
  <description>
    The secondary namenode HTTPS 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.namenode.http-bind-host</name>
  <value></value>
  <description>
    The actual adress the HTTP server will bind to. If this optional address
    is set, it overrides only the hostname portion of dfs.namenode.http-address.
    It can also be specified per name node or name service for HA/Federation.
    This is useful for making the name node HTTP server listen on all
    interfaces by setting it to 0.0.0.0.
  </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.client.cached.conn.retry</name>
  <value>3</value>
  <description>The number of times the HDFS client will pull a socket from the
   cache.  Once this number is exceeded, the client will try to create a new
   socket.
  </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.namenode.https-bind-host</name>
  <value></value>
  <description>
    The actual adress the HTTPS server will bind to. If this optional address
    is set, it overrides only the hostname portion of dfs.namenode.https-address.
    It can also be specified per name node or name service for HA/Federation.
    This is useful for making the name node HTTPS server listen on all
    interfaces by setting it to 0.0.0.0.
  </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>255</value>
  <description>Defines the maximum number of bytes in UTF-8 encoding 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>1048576</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.namenode.acls.enabled</name>
  <value>false</value>
  <description>
    Set to true to enable support for HDFS ACLs (Access Control Lists).  By
    default, ACLs are disabled.  When ACLs are disabled, the NameNode rejects
    all RPCs related to setting or getting ACLs.
  </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.client.block.write.replace-datanode-on-failure.best-effort</name>
  <value>false</value>
  <description>
    This property is used only if the value of
    dfs.client.block.write.replace-datanode-on-failure.enable is true.

    Best effort means that the client will try to replace a failed datanode
    in write pipeline (provided that the policy is satisfied), however, it 
    continues the write operation in case that the datanode replacement also
    fails.

    Suppose the datanode replacement fails.
    false: An exception should be thrown so that the write will fail.
    true : The write should be resumed with the remaining datandoes.
  
    Note that setting this property to true allows writing to a pipeline
    with a smaller number of datanodes.  As a result, it increases the
    probability of data loss.
  </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.blockreport.split.threshold</name>
    <value>1000000</value>
    <description>If the number of blocks on the DataNode is below this
    threshold then it will send block reports for all Storage Directories
    in a single message.

    If the number of blocks exceeds this threshold then the DataNode will
    send block reports for each Storage Directory in separate messages.

    Set to zero to always split.
    </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>60000</value>
  <description>
        Socket 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 successfully.
        This timeout prevents client hangs when the sender fails during
        image transfer. This is socket timeout during image tranfer.
  </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.image.transfer.chunksize</name>
  <value>65536</value>
  <description>
        Chunksize in bytes to upload the checkpoint.
        Chunked streaming is used to avoid internal buffering of contents
        of image file of huge size.
  </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.client.datanode-restart.timeout</name>
  <value>30</value>
  <description>
    Expert only. The time to wait, in seconds, from reception of an
    datanode shutdown notification for quick restart, until declaring
    the datanode dead and invoking the normal recovery mechanisms.
    The notification is sent by a datanode when it is being shutdown
    using the shutdownDatanode admin command with the upgrade option.
  </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.internal.nameservices</name>
  <value></value>
  <description>
    Comma-separated list of nameservices that belong to this cluster.
    Datanode will report to all the nameservices in this list. By default
    this is set to the value of dfs.nameservices.
  </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.datanode.shared.file.descriptor.paths</name>
  <value>/dev/shm,/tmp</value>
  <description>
    A comma-separated list of paths to use when creating file descriptors that
    will be shared between the DataNode and the DFSClient.  Typically we use
    /dev/shm, so that the file descriptors will not be written to disk.
    Systems that don't have /dev/shm will fall back to /tmp by default.
  </description>
</property>

<property>
  <name>dfs.short.circuit.shared.memory.watcher.interrupt.check.ms</name>
  <value>60000</value>
  <description>
    The length of time in milliseconds that the short-circuit shared memory
    watcher will go between checking for java interruptions sent from other
    threads.  This is provided mainly for unit tests.
  </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 &quot;stale&quot; 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 &quot;stale&quot; 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>nfs.server.port</name>
  <value>2049</value>
  <description>
      Specify the port number used by Hadoop NFS.
  </description>
</property>

<property>
  <name>nfs.mountd.port</name>
  <value>4242</value>
  <description>
      Specify the port number used by Hadoop mount daemon.
  </description>
</property>

<property>    
  <name>nfs.dump.dir</name>
  <value>/tmp/.hdfs-nfs</value>
  <description>
    This directory is used to temporarily save out-of-order writes before
    writing to HDFS. For each file, the out-of-order writes are dumped after
    they are accumulated to exceed certain threshold (e.g., 1MB) in memory. 
    One needs to make sure the directory has enough space.
  </description>
</property>

<property>
  <name>nfs.rtmax</name>
  <value>1048576</value>
  <description>This is the maximum size in bytes of a READ request
    supported by the NFS gateway. If you change this, make sure you
    also update the nfs mount's rsize(add rsize= # of bytes to the 
    mount directive).
  </description>
</property>

<property>
  <name>nfs.wtmax</name>
  <value>1048576</value>
  <description>This is the maximum size in bytes of a WRITE request
    supported by the NFS gateway. If you change this, make sure you
    also update the nfs mount's wsize(add wsize= # of bytes to the 
    mount directive).
  </description>
</property>

<property>
  <name>nfs.keytab.file</name>
  <value></value>
  <description>
    *Note*: Advanced property. Change with caution.
    This is the path to the keytab file for the hdfs-nfs gateway.
    This is required when the cluster is kerberized.
  </description>
</property>

<property>
  <name>nfs.kerberos.principal</name>
  <value></value>
  <description>
    *Note*: Advanced property. Change with caution.
    This is the name of the kerberos principal. This is required when
    the cluster is kerberized.It must be of this format:
    nfs-gateway-user/nfs-gateway-host@kerberos-realm
  </description>
</property>

<property>
  <name>nfs.allow.insecure.ports</name>
  <value>true</value>
  <description>
    When set to false, client connections originating from unprivileged ports
    (those above 1023) will be rejected. This is to ensure that clients
    connecting to this NFS Gateway must have had root privilege on the machine
    where they're connecting from.
  </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. It is possible to override this setting 
    per connection by specifying custom logic via dfs.trustedchannel.resolver.class. 
  </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.trustedchannel.resolver.class</name>
  <value></value>
  <description>
      TrustedChannelResolver is used to determine whether a channel 
      is trusted for plain data transfer. The TrustedChannelResolver is
      invoked on both client and server side. If the resolver indicates 
      that the channel is trusted, then the data transfer will not be 
      encrypted even if dfs.encrypt.data.transfer is set to true. The
      default implementation returns false indicating that the channel 
      is not trusted.
  </description>
</property>

<property>
  <name>dfs.data.transfer.protection</name>
  <value></value>
  <description>
    A comma-separated list of SASL protection values used for secured
    connections to the DataNode when reading or writing block data.  Possible
    values are authentication, integrity and privacy.  authentication means
    authentication only and no integrity or privacy; integrity implies
    authentication and integrity are enabled; and privacy implies all of
    authentication, integrity and privacy are enabled.  If
    dfs.encrypt.data.transfer is set to true, then it supersedes the setting for
    dfs.data.transfer.protection and enforces that all connections must use a
    specialized encrypted SASL handshake.  This property is ignored for
    connections to a DataNode listening on a privileged port.  In this case, it
    is assumed that the use of a privileged port establishes sufficient trust.
  </description>
</property>

<property>
  <name>dfs.data.transfer.saslproperties.resolver.class</name>
  <value></value>
  <description>
    SaslPropertiesResolver used to resolve the QOP used for a connection to the
    DataNode when reading or writing block data. If not specified, the value of
    hadoop.security.saslproperties.resolver.class is used as the default value.
  </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.millis</name>
  <value>1000</value>
  <description>
    Timeout (in milliseconds) 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 HTTP server listens on.
    If the port is 0 then the server will start on a free port.
  </description>
</property>

<property>
  <name>dfs.journalnode.https-address</name>
  <value>0.0.0.0:8481</value>
  <description>
    The address and port the JournalNode HTTPS server 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.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.enabled</name>
  <value>true</value>
  <description>
    If this is set to false, the client won't attempt to perform memory-mapped reads.
  </description>
</property>

<property>
  <name>dfs.client.mmap.cache.size</name>
  <value>256</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.

    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.

    Note that you can still do zero-copy reads when this size is set to 0.
  </description>
</property>

<property>
  <name>dfs.client.mmap.cache.timeout.ms</name>
  <value>3600000</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.client.mmap.retry.timeout.ms</name>
  <value>300000</value>
  <description>
    The minimum amount of time that we will wait before retrying a failed mmap
    operation.
  </description>
</property>

<property>
  <name>dfs.client.short.circuit.replica.stale.threshold.ms</name>
  <value>1800000</value>
  <description>
    The maximum amount of time that we will consider a short-circuit replica to
    be valid, if there is no communication from the DataNode.  After this time
    has elapsed, we will re-fetch the short-circuit replica even if it is in
    the cache.
  </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>30000</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 30 seconds.
  </description>
</property>

<property>
  <name>dfs.namenode.path.based.cache.retry.interval.ms</name>
  <value>30000</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>

<property>
  <name>dfs.client.context</name>
  <value>default</value>
  <description>
    The name of the DFSClient context that we should use.  Clients that share
    a context share a socket cache and short-circuit cache, among other things.
    You should only change this if you don't want to share with another set of
    threads.
  </description>
</property>

<property>
  <name>dfs.client.read.shortcircuit</name>
  <value>false</value>
  <description>
    This configuration parameter turns on short-circuit local reads.
  </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.client.read.shortcircuit.skip.checksum</name>
  <value>false</value>
  <description>
    If this configuration parameter is set,
    short-circuit local reads will skip checksums.
    This is normally not recommended,
    but it may be useful for special setups.
    You might consider using this
    if you are doing your own checksumming outside of HDFS.
  </description>
</property>

<property>
  <name>dfs.client.read.shortcircuit.streams.cache.size</name>
  <value>256</value>
  <description>
    The DFSClient maintains a cache of recently opened file descriptors.
    This parameter controls the size of that cache.
    Setting this higher will use more file descriptors,
    but potentially provide better performance on workloads
    involving lots of seeks.
  </description>
</property>

<property>
  <name>dfs.client.read.shortcircuit.streams.cache.expiry.ms</name>
  <value>300000</value>
  <description>
    This controls the minimum amount of time
    file descriptors need to sit in the client cache context
    before they can be closed for being inactive for too long.
  </description>
</property>

<property>
  <name>dfs.datanode.shared.file.descriptor.paths</name>
  <value>/dev/shm,/tmp</value>
  <description>
    Comma separated paths to the directory on which
    shared memory segments are created.
    The client and the DataNode exchange information via
    this shared memory segment.
    It tries paths in order until creation of shared memory segment succeeds.
  </description>
</property>

<property>
  <name>dfs.client.use.legacy.blockreader.local</name>
  <value>false</value>
  <description>
    Legacy short-circuit reader implementation based on HDFS-2246 is used
    if this configuration parameter is true.
    This is for the platforms other than Linux
    where the new implementation based on HDFS-347 is not available.
  </description>
</property>

<property>
  <name>dfs.block.local-path-access.user</name>
  <value></value>
  <description>
    Comma separated list of the users allowd to open block files
    on legacy short-circuit local read.
  </description>
</property>

<property>
  <name>dfs.client.domain.socket.data.traffic</name>
  <value>false</value>
  <description>
    This control whether we will try to pass normal data traffic
    over UNIX domain socket rather than over TCP socket
    on node-local data transfer.
    This is currently experimental and turned off by default.
  </description>
</property>

<property>
  <name>dfs.namenode.reject-unresolved-dn-topology-mapping</name>
  <value>false</value>
  <description>
    If the value is set to true, then namenode will reject datanode 
    registration if the topology mapping for a datanode is not resolved and 
    NULL is returned (script defined by net.topology.script.file.name fails 
    to execute). Otherwise, datanode will be registered and the default rack 
    will be assigned as the topology path. Topology paths are important for 
    data resiliency, since they define fault domains. Thus it may be unwanted 
    behavior to allow datanode registration with the default rack if the 
    resolving topology failed.
  </description>
</property>

<property>
  <name>dfs.namenode.xattrs.enabled</name>
  <value>true</value>
  <description>
    Whether support for extended attributes is enabled on the NameNode.
  </description>
</property>

<property>
  <name>dfs.namenode.fs-limits.max-xattrs-per-inode</name>
  <value>32</value>
  <description>
    Maximum number of extended attributes per inode.
  </description>
</property>

<property>
  <name>dfs.namenode.fs-limits.max-xattr-size</name>
  <value>16384</value>
  <description>
    The maximum combined size of the name and value of an extended attribute in bytes.
  </description>
</property>

<property>
  <name>dfs.client.slow.io.warning.threshold.ms</name>
  <value>30000</value>
  <description>The threshold in milliseconds at which we will log a slow
    io warning in a dfsclient. By default, this parameter is set to 30000
    milliseconds (30 seconds).
  </description>
</property>

<property>
  <name>dfs.datanode.slow.io.warning.threshold.ms</name>
  <value>300</value>
  <description>The threshold in milliseconds at which we will log a slow
    io warning in a datanode. By default, this parameter is set to 300
    milliseconds.
  </description>
</property>

<property>
  <name>dfs.namenode.startup.delay.block.deletion.sec</name>
  <value>0</value>
  <description>The delay in seconds at which we will pause the blocks deletion
    after Namenode startup. By default it's disabled.
    In the case a directory has large number of directories and files are
    deleted, suggested delay is one hour to give the administrator enough time
    to notice large number of pending deletion blocks and take corrective
    action.
  </description>
</property>

<property>
  <name>dfs.namenode.randomize-block-locations-per-block</name>
  <value>false</value>
  <description>When fetching replica locations of a block, the replicas
   are sorted based on network distance. This configuration parameter
   determines whether the replicas at the same network distance are randomly
   shuffled. By default, this is false, such that repeated requests for a block's
   replicas always result in the same order. This potentially improves page cache
   behavior. However, for some network topologies, it is desirable to shuffle this
   order for better load balancing.
  </description>
</property>

<property>
  <name>dfs.datanode.block.id.layout.upgrade.threads</name>
  <value>12</value>
  <description>The number of threads to use when creating hard links from
    current to previous blocks during upgrade of a DataNode to block ID-based
    block layout (see HDFS-6482 for details on the layout).</description>
</property>

<property>
  <name>dfs.namenode.list.encryption.zones.num.responses</name>
  <value>100</value>
  <description>When listing encryption zones, the maximum number of zones
    that will be returned in a batch. Fetching the list incrementally in
    batches improves namenode performance.
  </description>
</property>

<property>
  <name>dfs.namenode.inotify.max.events.per.rpc</name>
  <value>1000</value>
  <description>Maximum number of events that will be sent to an inotify client
    in a single RPC response. The default value attempts to amortize away
    the overhead for this RPC while avoiding huge memory requirements for the
    client and NameNode (1000 events should consume no more than 1 MB.)
  </description>
</property>

<property>
  <name>dfs.user.home.dir.prefix</name>
  <value>/user</value>
  <description>The directory to prepend to user name to get the user's
    home direcotry.
  </description>
</property>

<property>
  <name>dfs.datanode.cache.revocation.timeout.ms</name>
  <value>900000</value>
  <description>When the DFSClient reads from a block file which the DataNode is
    caching, the DFSClient can skip verifying checksums.  The DataNode will
    keep the block file in cache until the client is done.  If the client takes
    an unusually long time, though, the DataNode may need to evict the block
    file from the cache anyway.  This value controls how long the DataNode will
    wait for the client to release a replica that it is reading without
    checksums.
  </description>
</property>

<property>
  <name>dfs.datanode.cache.revocation.polling.ms</name>
  <value>500</value>
  <description>How often the DataNode should poll to see if the clients have
    stopped using a replica that the DataNode wants to uncache.
  </description>
</property>

</configuration>