hadoop2 | 易学教程

How does Hadoop decide how many nodes will perform the Map and Reduce tasks?

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问题 I'm new to hadoop and I'm trying to understand it. Im talking about hadoop 2. When I have an input file which I wanto to do a MapReduce, in the MapReduce programm I say the parameter of the Split, so it will make as many map tasks as splits,right? The resource manager knows where the files are and will send the tasks to the nodes who have the data, but who says how many nodes will do the tasks? After the maps are donde there is the shuffle, which node will do a reduce task is decided by the

Could not find or load main class com.sun.tools.javac.Main hadoop mapreduce

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问题 I am trying to learn MapReduce but I am a little lost right now. http://hadoop.apache.org/docs/r2.6.0/hadoop-mapreduce-client/hadoop-mapreduce-client-core/MapReduceTutorial.html#Usage Particularly this set of instructions: Compile WordCount.java and create a jar: $ bin/hadoop com.sun.tools.javac.Main WordCount.java When I type in hadoop in my terminal I am able to see the "Help" made which provides arguments so I believe I have hadoop installed. When I type in the command: Compile WordCount

yarn is not honouring yarn.nodemanager.resource.cpu-vcores

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问题 I am using Hadoop-2.4.0 and my system configs are 24 cores, 96 GB RAM. I am using following configs mapreduce.map.cpu.vcores=1 yarn.nodemanager.resource.cpu-vcores=10 yarn.scheduler.minimum-allocation-vcores=1 yarn.scheduler.maximum-allocation-vcores=4 yarn.app.mapreduce.am.resource.cpu-vcores=1 yarn.nodemanager.resource.memory-mb=88064 mapreduce.map.memory.mb=3072 mapreduce.map.java.opts=-Xmx2048m Capacity Scheduler configs queue.default.capacity=50 queue.default.maximum_capacity=100 yarn

How can I access S3/S3n from a local Hadoop 2.6 installation?

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I am trying to reproduce an Amazon EMR cluster on my local machine. For that purpose, I have installed the latest stable version of Hadoop as of now - 2.6.0 . Now I would like to access an S3 bucket, as I do inside the EMR cluster. I have added the aws credentials in core-site.xml: <property> <name>fs.s3.awsAccessKeyId</name> <value>some id</value> </property> <property> <name>fs.s3n.awsAccessKeyId</name> <value>some id</value> </property> <property> <name>fs.s3.awsSecretAccessKey</name> <value>some key</value> </property> <property> <name>fs.s3n.awsSecretAccessKey</name> <value>some key<

Hadoop 2.0 data write operation acknowledgement

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问题 I have a small query regarding hadoop data writes From Apache documentation For the common case, when the replication factor is three, HDFS’s placement policy is to put one replica on one node in the local rack, another on a node in a different (remote) rack, and the last on a different node in the same remote rack. This policy cuts the inter-rack write traffic which generally improves write performance. The chance of rack failure is far less than that of node failure; In below image, when

How does Hadoop Namenode failover process works?

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问题 Hadoop defintive guide says - Each Namenode runs a lightweight failover controller process whose job it is to monitor its Namenode for failures (using a simple heartbeat mechanism) and trigger a failover should a namenode fail. How come a namenode can run something to detect its own failure? Who sends heartbeat to whom? Where this process runs? How it detects namenode failure? To whom it notify for the transition? 回答1: From Apache docs The ZKFailoverController (ZKFC) is a new component which

Hadoop “Unable to load native-hadoop library for your platform” warning

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问题 I\'m currently configuring hadoop on a server running CentOs . When I run start-dfs.sh or stop-dfs.sh , I get the following error: WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable I\'m running Hadoop 2.2.0. Doing a search online brought up this link: http://balanceandbreath.blogspot.ca/2013/01/utilnativecodeloader-unable-to-load.html However, the contents of /native/ directory on hadoop 2.x appear to be different