MapReduce

问题 How to change the number of data nodes, that is disable and enable certain data nodes to test scalability? To be more clear, I have 4 data nodes, and I want to experiment the performance with 1, 2, 3 and 4 data nodes one by one. Would it be possible just updating slaves file in namenode? 回答1: The correct way to temporarily decommission a node: Create an "exclude file". This lists the hosts, one per line, that you wish to remove. Set dfs.hosts.exclude and mapred.hosts.exclude to the location

问题 I am new to Hadoop and I want to run a MapReduce job. However, I've got the error that the hadoop can not find the mapper class. This is the error: INFO mapred.JobClient: Task Id : attempt_201608292140_0023_m_000000_0, Status : FAILED java.lang.RuntimeException: java.lang.ClassNotFoundException: TransMapper1 at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:857) at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199) at org.apache.hadoop.mapred.MapTask

问题 After upgrade of cassandra from 0.8.2 to 0.8.4, got this error I have restarted cassandra, removed data, etc. nothing helps I have 6 identical machines in the cloud, before it was working fine. If I make netstat then it shows port 9160 listening nodetool ... ring - responces with 6 machines UP. what could be the problem? : ( Exception in thread "main" java.io.IOException: Could not get input splits at org.apache.cassandra.hadoop.ColumnFamilyInputFormat.getSplits(ColumnFamilyInputFormat.java

问题 This is what I am doing: public class MOPartition extends Partitioner<Text, Text> { public MOPartition() {} ... } Error: java.lang.RuntimeException: java.lang.NoSuchMethodException: globalSort$MOPartition.() Even defining a empty constructor didnt help. I then Googled it and came across following link http://lucene.472066.n3.nabble.com/preserve-JobTracker-information-td826974.html. I then checked my JRE version and it is 1.6.0.26. So, I think I am pretty much safe as far JRE is concerned. Can

问题 This is a follow up question of Extracting rows containing specific value using mapReduce and hadoop Mapper function public static class MapForWordCount extends Mapper<Object, Text, Text, IntWritable>{ private IntWritable saleValue = new IntWritable(); private Text rangeValue = new Text(); public void map(Object key, Text value, Context con) throws IOException, InterruptedException { String line = value.toString(); String[] words = line.split(","); for(String word: words ) { if(words[3]

问题 I have a RavenDB database with two document collections. I need to combine documents from these two into a single business entity using a multi map/reduce index. The business entity isn't complete if I don't combine the two collections. You could probably argue that this indicates that my domain model or data model is broken but it is what it is and there isn't anythig I can do about it. So, on with the question :-). Basically the three documents: { // RootDocuments/1 "Foo" : "Bar", "Bar" :

问题 I am invoking mapreduce job from my java program. Today, when I set the mapreduce job's input fromat to : LzoTextInputFormat The mapreduce job fail: Could not load native gpl library java.lang.UnsatisfiedLinkError: no gplcompression in java.library.path at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1738) at java.lang.Runtime.loadLibrary0(Runtime.java:823) at java.lang.System.loadLibrary(System.java:1028) at com.hadoop.compression.lzo.GPLNativeCodeLoader.<clinit>(GPLNativeCodeLoader

问题 I am new to Hadoop and MapReduce. I have some directory and files within this (each file 10 MB big and N could be 100. Files may be compressed or uncompressed) like: MyDir1/file1 MyDir1/file2 ... MyDir1/fileN MyDir2/file1 MyDir2/file2 ... MyDir3/fileN I want to design a MapReduce application where one mapper or reducer would process entire MyDir1 i.e. I dont want the MyDir1 to be split across multiple mappers. Similarly I want MyDir2 to be processed by other mapper/reducer completely without

问题 I want to do a copy text files from external sources to HDFS. Lets assume that I can combine and split the files based on their size, what should be the size of the text file for best custom Map Reduce job performance. Does size matter ? 回答1: HDFS is designed to support very large files not small files. Applications that are compatible with HDFS are those that deal with large data sets. These applications write their data only once but they read it one or more times and require these reads to

问题 We would like our application logs to be printed to files on the local nodes. We're using Log4j's RollingFileAppender. Our log4j.properties file is as follows: ODS.LOG.DIR=/var/log/appLogs ODS.LOG.INFO.FILE=application.log ODS.LOG.ERROR.FILE=application_error.log # Root logger option log4j.rootLogger=ERROR, console log4j.logger.com.ournamespace=ERROR, APP_APPENDER, ERROR_APPENDER # # console # Add "console" to rootlogger above if you want to use this # log4j.appender.console=org.apache.log4j