Hadoop 2.2.0配置文件：hdfs-default.xml

name	value	description
hadoop.hdfs.configuration.version	1	配置文件版本
dfs.namenode.logging.level	info	dfs namenode的日志级别。 其他值包括"dir"（跟踪命名空间的变化），"block"（跟踪复制时的块变化和块创建/删除操作），"all"
dfs.namenode.rpc-address		RPC(远程过程调用)地址，处理所有客户端请求。在HA/Federation情景下，存在多个namenode，name的服务id被添加到name后。如，dfs.namenode.rpc-address.ns1。 value的形式为nn-host1:rpc-port
dfs.namenode.rpc-bind-host		服务器实际绑定的地址。如果设置该选项，RPC服务器会绑定该地址和dfs.namenode.rpc-address中设定的端口。HA/Federation场景下，可以为每一个name node指定一个地址。通过设置该值为0.0.0.0可以使name node监听所有的网络接口
dfs.namenode.servicerpc-address		HDFS服务通讯的RPC地址。如果设置该值，备份结点、数据结点和其他服务将会连接到指定地址。HA/Federation场景下，name服务id添加到name后面。如，dfs.namenode.servicerpc-address.ns1 value的形式为nn-host1:rpc-port。如果该值未设置，则默认为dfs.namenode.rpc-address
dfs.namenode.servicerpc-bind-host		服务器实际绑定的地址。如果设置该选项，提供HDFS服务的RPC服务器会绑定该地址和dfs.namenode.servicerpc-address中设定的端口。 其他含义同dfs.namenode.rpc-bind-host
dfs.namenode.secondary.http-address	0.0.0.0:50090	次命名结点http服务器地址和端口
dfs.datanode.address	0.0.0.0:50010	数据结点进行数据传输的服务器地址和端口
dfs.datanode.http.address	0.0.0.0:50075	数据结点的http服务器地址和端口
dfs.datanode.ipc.address	0.0.0.0:50020	数据结点的ipc服务器地址和端口
dfs.datanode.handler.count	10	数据结点的服务线程数
dfs.namenode.http-address	0.0.0.0:50070	dfs命名结点web ui监听的地址和端口
dfs.https.enable	false	HDFS是否支持HTTPS(SSL)
dfs.client.https.need-auth	false	是否需要SSL客户端证书
dfs.https.server.keystore.resource	ssl-server.xml	SSL服务器keystore信息资源文件
dfs.client.https.keystore.resource	ssl-client.xml	SSL客户端keystore信息资源文件
dfs.datanode.https.address	0.0.0.0:50475	数据结点https服务器地址和端口
dfs.namenode.https-address	0.0.0.0:50470	命名结点https服务器地址和端口
dfs.datanode.dns.interface	default	数据结点上报IP地址的网络接口名称
dfs.datanode.dns.nameserver	default	DNS主机名或IP地址，供数据结点与命名结点主机名通讯和显示
dfs.namenode.backup.address	0.0.0.0:50100	备份结点服务器地址和端口。端口为0时，服务器使用一个空闲端口
dfs.namenode.backup.http-address	0.0.0.0:50105	备份结点的http服务器地址和结点。端口为0时，服务器使用一个空闲端口
dfs.namenode.replication.considerLoad	true	选择目标结点时是否考虑其负载情况
dfs.default.chunk.view.size	32768	浏览器显示文件时的显示字节数
dfs.datanode.du.reserved	0	每个卷的保存空间（字节数）。常常设置为较大的空间供dfs外使用
dfs.namenode.name.dir	file://${hadoop.tmp.dir}/dfs/name	DFS存储命名表（fsimage）的本地文件系统路径。以逗号分隔多个路径时，命名表会被复制到所有路径来保证冗余
dfs.namenode.name.dir.restore	false	设置为true时，命名结点尝试恢复之前失败的dfs.namenode.name.dir。 该选项启用时，在检查点将会尝试恢复所有失败的目录
dfs.namenode.fs-limits.max-component-length	0	Defines the maximum number of characters in each component of a path. A value of 0 will disable the check.
dfs.namenode.fs-limits.max-directory-items	0	Defines the maximum number of items that a directory may contain. A value of 0 will disable the check.
dfs.namenode.fs-limits.min-block-size	1048576	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.
dfs.namenode.fs-limits.max-blocks-per-file	1048576	Maximum number of blocks per file, enforced by the Namenode on write. This prevents the creation of extremely large files which can degrade performance.
dfs.namenode.edits.dir	${dfs.namenode.name.dir}	Determines where on the local filesystem the DFS name node should store the transaction (edits) file. If this is a comma-delimited list of directories then the transaction file is replicated in all of the directories, for redundancy. Default value is same as dfs.namenode.name.dir
dfs.namenode.shared.edits.dir		A directory on shared storage between the multiple namenodes in an HA cluster. This directory will be written by the active and read by the standby in order to keep the namespaces synchronized. This directory does not need to be listed in dfs.namenode.edits.dir above. It should be left empty in a non-HA cluster.
dfs.namenode.edits.journal-plugin.qjournal	org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager
dfs.permissions.enabled	true	If "true", enable permission checking in HDFS. If "false", permission checking is turned off, but all other behavior is unchanged. Switching from one parameter value to the other does not change the mode, owner or group of files or directories.
dfs.permissions.superusergroup	supergroup	The name of the group of super-users.
dfs.block.access.token.enable	false	If "true", access tokens are used as capabilities for accessing datanodes. If "false", no access tokens are checked on accessing datanodes.
dfs.block.access.key.update.interval	600	Interval in minutes at which namenode updates its access keys.
dfs.block.access.token.lifetime	600	The lifetime of access tokens in minutes.
dfs.datanode.data.dir	file://${hadoop.tmp.dir}/dfs/data	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.
dfs.datanode.data.dir.perm	700	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.
dfs.replication	3	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.
dfs.replication.max	512	Maximal block replication.
dfs.namenode.replication.min	1	Minimal block replication.
dfs.blocksize	134217728	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).
dfs.client.block.write.retries	3	The number of retries for writing blocks to the data nodes, before we signal failure to the application.
dfs.client.block.write.replace-datanode-on-failure.enable	true	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
dfs.client.block.write.replace-datanode-on-failure.policy	DEFAULT	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.
dfs.blockreport.intervalMsec	21600000	Determines block reporting interval in milliseconds.
dfs.blockreport.initialDelay	0	Delay for first block report in seconds.
dfs.datanode.directoryscan.interval	21600	Interval in seconds for Datanode to scan data directories and reconcile the difference between blocks in memory and on the disk.
dfs.datanode.directoryscan.threads	1	How many threads should the threadpool used to compile reports for volumes in parallel have.
dfs.heartbeat.interval	3	Determines datanode heartbeat interval in seconds.
dfs.namenode.handler.count	10	The number of server threads for the namenode.
dfs.namenode.safemode.threshold-pct	0.999f	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.
dfs.namenode.safemode.min.datanodes	0	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.
dfs.namenode.safemode.extension	30000	Determines extension of safe mode in milliseconds after the threshold level is reached.
dfs.datanode.balance.bandwidthPerSec	1048576	Specifies the maximum amount of bandwidth that each datanode can utilize for the balancing purpose in term of the number of bytes per second.
dfs.hosts		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.
dfs.hosts.exclude		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.
dfs.namenode.max.objects	0	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.
dfs.namenode.decommission.interval	30	Namenode periodicity in seconds to check if decommission is complete.
dfs.namenode.decommission.nodes.per.interval	5	The number of nodes namenode checks if decommission is complete in each dfs.namenode.decommission.interval.
dfs.namenode.replication.interval	3	The periodicity in seconds with which the namenode computes repliaction work for datanodes.
dfs.namenode.accesstime.precision	3600000	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.
dfs.datanode.plugins		Comma-separated list of datanode plug-ins to be activated.
dfs.namenode.plugins		Comma-separated list of namenode plug-ins to be activated.
dfs.stream-buffer-size	4096	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.
dfs.bytes-per-checksum	512	The number of bytes per checksum. Must not be larger than dfs.stream-buffer-size
dfs.client-write-packet-size	65536	Packet size for clients to write
dfs.client.write.exclude.nodes.cache.expiry.interval.millis	600000	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.
dfs.namenode.checkpoint.dir	file://${hadoop.tmp.dir}/dfs/namesecondary	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.
dfs.namenode.checkpoint.edits.dir	${dfs.namenode.checkpoint.dir}	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
dfs.namenode.checkpoint.period	3600	The number of seconds between two periodic checkpoints.
dfs.namenode.checkpoint.txns	1000000	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.
dfs.namenode.checkpoint.check.period	60	The SecondaryNameNode and CheckpointNode will poll the NameNode every 'dfs.namenode.checkpoint.check.period' seconds to query the number of uncheckpointed transactions.
dfs.namenode.checkpoint.max-retries	3	The SecondaryNameNode retries failed checkpointing. If the failure occurs while loading fsimage or replaying edits, the number of retries is limited by this variable.
dfs.namenode.num.checkpoints.retained	2	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.
dfs.namenode.num.extra.edits.retained	1000000	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.
dfs.namenode.max.extra.edits.segments.retained	10000	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.
dfs.namenode.delegation.key.update-interval	86400000	The update interval for master key for delegation tokens in the namenode in milliseconds.
dfs.namenode.delegation.token.max-lifetime	604800000	The maximum lifetime in milliseconds for which a delegation token is valid.
dfs.namenode.delegation.token.renew-interval	86400000	The renewal interval for delegation token in milliseconds.
dfs.datanode.failed.volumes.tolerated	0	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.
dfs.image.compress	false	Should the dfs image be compressed?
dfs.image.compression.codec	org.apache.hadoop.io.compress.DefaultCodec	If the dfs image is compressed, how should they be compressed? This has to be a codec defined in io.compression.codecs.
dfs.image.transfer.timeout	600000	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.
dfs.image.transfer.bandwidthPerSec	0	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.
dfs.namenode.support.allow.format	true	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.
dfs.datanode.max.transfer.threads	4096	Specifies the maximum number of threads to use for transferring data in and out of the DN.
dfs.datanode.readahead.bytes	4193404	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.
dfs.datanode.drop.cache.behind.reads	false	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.
dfs.datanode.drop.cache.behind.writes	false	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.
dfs.datanode.sync.behind.writes	false	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.
dfs.client.failover.max.attempts	15	Expert only. The number of client failover attempts that should be made before the failover is considered failed.
dfs.client.failover.sleep.base.millis	500	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.
dfs.client.failover.sleep.max.millis	15000	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.
dfs.client.failover.connection.retries	0	Expert only. Indicates the number of retries a failover IPC client will make to establish a server connection.
dfs.client.failover.connection.retries.on.timeouts	0	Expert only. The number of retry attempts a failover IPC client will make on socket timeout when establishing a server connection.
dfs.nameservices		Comma-separated list of nameservices.
dfs.nameservice.id		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.
dfs.ha.namenodes.EXAMPLENAMESERVICE		The prefix for a given nameservice, contains a comma-separated list of namenodes for a given nameservice (eg EXAMPLENAMESERVICE).
dfs.ha.namenode.id		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.
dfs.ha.log-roll.period	120	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.
dfs.ha.tail-edits.period	60	How often, in seconds, the StandbyNode should check for new finalized log segments in the shared edits log.
dfs.ha.automatic-failover.enabled	false	Whether automatic failover is enabled. See the HDFS High Availability documentation for details on automatic HA configuration.
dfs.support.append	true	Does HDFS allow appends to files?
dfs.client.use.datanode.hostname	false	Whether clients should use datanode hostnames when connecting to datanodes.
dfs.datanode.use.datanode.hostname	false	Whether datanodes should use datanode hostnames when connecting to other datanodes for data transfer.
dfs.client.local.interfaces		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).
dfs.namenode.kerberos.internal.spnego.principal	${dfs.web.authentication.kerberos.principal}
dfs.secondary.namenode.kerberos.internal.spnego.principal	${dfs.web.authentication.kerberos.principal}
dfs.namenode.avoid.read.stale.datanode	false	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.
dfs.namenode.avoid.write.stale.datanode	false	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.
dfs.namenode.stale.datanode.interval	30000	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).
dfs.namenode.write.stale.datanode.ratio	0.5f	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.
dfs.namenode.invalidate.work.pct.per.iteration	0.32f	*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%.
dfs.namenode.replication.work.multiplier.per.iteration	2	*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.
dfs.webhdfs.enabled	false	Enable WebHDFS (REST API) in Namenodes and Datanodes.
hadoop.fuse.connection.timeout	300	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.
hadoop.fuse.timer.period	5	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.
dfs.metrics.percentiles.intervals		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.
dfs.encrypt.data.transfer	false	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.
dfs.encrypt.data.transfer.algorithm		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.
dfs.datanode.hdfs-blocks-metadata.enabled	false	Boolean which enables backend datanode-side support for the experimental DistributedFileSystem#getFileVBlockStorageLocations API.
dfs.client.file-block-storage-locations.num-threads	10	Number of threads used for making parallel RPCs in DistributedFileSystem#getFileBlockStorageLocations().
dfs.client.file-block-storage-locations.timeout	60	Timeout (in seconds) for the parallel RPCs made in DistributedFileSystem#getFileBlockStorageLocations().
dfs.journalnode.rpc-address	0.0.0.0:8485	The JournalNode RPC server address and port.
dfs.journalnode.http-address	0.0.0.0:8480	The address and port the JournalNode web UI listens on. If the port is 0 then the server will start on a free port.
dfs.namenode.audit.loggers	default	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.
dfs.domain.socket.path		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.
dfs.datanode.available-space-volume-choosing-policy.balanced-space-threshold	10737418240	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.
dfs.datanode.available-space-volume-choosing-policy.balanced-space-preference-fraction	0.75f	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.
dfs.namenode.edits.noeditlogchannelflush	false	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.
dfs.client.cache.drop.behind.writes		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.
dfs.client.cache.drop.behind.reads		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.
dfs.client.cache.readahead		Just like dfs.datanode.readahead.bytes, 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. If the native libraries are not available to the DataNode, this configuration has no effect.
dfs.namenode.enable.retrycache	true	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.
dfs.namenode.retrycache.expirytime.millis	600000	The time for which retry cache entries are retained.
dfs.namenode.retrycache.heap.percent	0.03f	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.

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