hadoop.hdfs.configuration.version 1 version of this configuration file dfs.namenode.logging.level info 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". dfs.namenode.rpc-address 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. dfs.namenode.rpc-bind-host The actual address the server will bind to. If this optional address is set, the RPC server will bind to this address and the port specified in dfs.namenode.rpc-address for the RPC server. It can also be specified per name node or name service for HA/Federation. This is most useful for making name node listen to all interfaces by setting to 0.0.0.0. dfs.namenode.servicerpc-address 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. dfs.namenode.servicerpc-bind-host The actual address the server will bind to. If this optional address is set, the service RPC server will bind to this address and the port specified in dfs.namenode.servicerpc-address. It can also be specified per name node or name service for HA/Federation. This is most useful for making name node listen to all interfaces by setting to 0.0.0.0. dfs.namenode.secondary.http-address 0.0.0.0:50090 The secondary namenode http server address and port. dfs.datanode.address 0.0.0.0:50010 The datanode server address and port for data transfer. dfs.datanode.http.address 0.0.0.0:50075 The datanode http server address and port. dfs.datanode.ipc.address 0.0.0.0:50020 The datanode ipc server address and port. dfs.datanode.handler.count 10 The number of server threads for the datanode. dfs.namenode.http-address 0.0.0.0:50070 The address and the base port where the dfs namenode web ui will listen on. dfs.https.enable false Decide if HTTPS(SSL) is supported on HDFS dfs.client.https.need-auth false Whether SSL client certificate authentication is required dfs.https.server.keystore.resource ssl-server.xml Resource file from which ssl server keystore information will be extracted dfs.client.https.keystore.resource ssl-client.xml Resource file from which ssl client keystore information will be extracted dfs.datanode.https.address 0.0.0.0:50475 The datanode secure http server address and port. dfs.namenode.https-address 0.0.0.0:50470 The namenode secure http server address and port. dfs.datanode.dns.interface default The name of the Network Interface from which a data node should report its IP address. dfs.datanode.dns.nameserver default 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. dfs.namenode.backup.address 0.0.0.0:50100 The backup node server address and port. If the port is 0 then the server will start on a free port. dfs.namenode.backup.http-address 0.0.0.0:50105 The backup node http server address and port. If the port is 0 then the server will start on a free port. dfs.namenode.replication.considerLoad true Decide if chooseTarget considers the target's load or not dfs.default.chunk.view.size 32768 The number of bytes to view for a file on the browser. dfs.datanode.du.reserved 0 Reserved space in bytes per volume. Always leave this much space free for non dfs use. dfs.namenode.name.dir file://${hadoop.tmp.dir}/dfs/name 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. dfs.namenode.name.dir.restore false 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. 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.datanode.registration.ip-hostname-check true 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. 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. dfs.client.mmap.cache.size 1024 When zero-copy reads are used, the DFSClient keeps a cache of recently used memory mapped regions. This parameter controls the maximum number of entries that we will keep in that cache. If this is set to 0, we will not allow mmap. The larger this number is, the more file descriptors we will potentially use for memory-mapped files. mmaped files also use virtual address space. You may need to increase your ulimit virtual address space limits before increasing the client mmap cache size. dfs.client.mmap.cache.timeout.ms 900000 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. dfs.namenode.caching.enabled false Set to true to enable block caching. This flag enables the NameNode to maintain a mapping of cached blocks to DataNodes via processing DataNode cache reports. Based on these reports and addition and removal of caching directives, the NameNode will schedule caching and uncaching work. dfs.datanode.max.locked.memory 0 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. dfs.namenode.list.cache.directives.num.responses 100 This value controls the number of cache directives that the NameNode will send over the wire in response to a listDirectives RPC. dfs.namenode.list.cache.pools.num.responses 100 This value controls the number of cache pools that the NameNode will send over the wire in response to a listPools RPC. dfs.namenode.path.based.cache.refresh.interval.ms 300000 The amount of milliseconds between subsequent path cache rescans. Path cache rescans are when we calculate which blocks should be cached, and on what datanodes. By default, this parameter is set to 300000, which is five minutes. dfs.datanode.fsdatasetcache.max.threads.per.volume 4 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. dfs.cachereport.intervalMsec 10000 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. dfs.namenode.edit.log.autoroll.multiplier.threshold 2.0 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. dfs.namenode.edit.log.autoroll.check.interval.ms 300000 How often an active namenode will check if it needs to roll its edit log, in milliseconds.