mapreduce algorithm in hadoop

The example Terasort in Hadoop is an example of sorting using Mapredue. This article references and simplifies this example: The basic idea of sequencing is to take advantage of the automatic sequencing of MapReduce, in Hadoop, from the map to the reduce phase, the map structure will be assigned to each key according to the hash value of each reduce, wherein in r

PriviledgedActionException as:man (auth:SIMPLE) cause:java.io.IOException: Cannot initialize Cluster. Please check your configuration for mapreduce.framework.name and the correspond server addresses.2014-09-24 12:57:41,567 ERROR [RunService.java:206] - [thread-id:17 thread-name:Thread-6] threadId:17,Excpetion:java.io.IOException: Cannot initialize Cluster. Please check your configuration for mapreduce.framework.name and the correspond server addresses.at org.apache.hadoop.mapreduce.Cluster.initi

precedence is higher than the attribute defined by the file resource To override a property by using the JVM parameter -dproperty=value on the command line Second, configure the development environment CONF option: Easy to switch configuration files Genericoptionsparser,tool and Toolrunner: Genericoptionsparser A class that explains common Hadoop command-line options, which can be set in the configuration object depending on th

procedureMake the Java program into a jar package and upload it to the Hadoop server (any Namenode node on the boot)3. Data sourceThe data source is as follows:Hadoop java text hdfstom Jack Java textjob hadoop ABC lusihdfs Tom textPut the content in a TXT file and put it in HDFs/usr/input (under HDFs, not Linux), and you can upload it using the Eclipse plugin:4. Execute JAR Package# fully qualified name

. ManagementThe Fair Scheduler provides support for two mechanisms for execution-time management: By editing the allocation file, you can change the minimum share, limit, weight, pre-occupancy time difference, and queue scheduling policy.The scheduler will reload the file 10-15 seconds after it knows it has changed. The current app, queue, and fair share can be checked through the ResourceManager Web interface, which is http://ResourceManager URL/cluster/scheduler.Each of the following qu

); 5 Sort grouping//6 set in a certain reduce and key value type Job.setreducerclass (Myreduce.class); Job.setoutputkeyclass (Longwritable.class); Job.setoutputvalueclass (longwritable.cLASS); 7 Set Output directory Fileoutputformat.setoutputpath (Job, New Path (Output_dir)); 8 Submit Job Job.waitforcompletion (TRUE); } static void Deleteoutputfile (String path) throws exception{Configuration conf = new configuration (); FileSystem fs = Filesystem.get (new U

0 Basic Learning Hadoop to get started work line guide beginner: Hive and MapReduce: http://www.aboutyun.com/thread-7567-1-1.htmlMapReduce Learning Catalog SummaryMApreduce Learning Guide and Troubleshooting summary : http://www.aboutyun.com/thread-7091-1-1.htmlWhat is map/reduce:http://www.aboutyun.com/thread-5541-1-1.htmlMapreduce whole working mechanism diagram: http://www.aboutyun.com/thread-5641-1-1.h

As input When the compressed file is MapReduce input, MapReduce will automatically extract the corresponding codec from the extension. As output When the MapReduce output file requires compression, you can change mapred.output.compress to True, Mapped.output.compression.codec the class name for the codec you want to use Yes, of course you can specify in the c

description and submission classespublic class Flowsumrunner extends configured implements tool{public int run (string[] arg0) throws Exception {Configuration conf = new configuration ();Job Job = job.getinstance (conf);Job.setjarbyclass (Flowsumrunner.class);Job.setmapperclass (Flowsummapper.class);Job.setreducerclass (Flowsumreducer.class);Job.setmapoutputkeyclass (Text.class);Job.setmapoutputvalueclass (Flowbean.class);Job.setoutputkeyclass (Text.class);Job.setoutputvalueclass (Flowbean.clas

Hadoop beginners often have two questions: 1. If a hadoop block is 64 MB by default, will a row of records be divided into two blocks for text in the form of a record row? 2. when a file is read from the block for splitting, will a row of records be divided into two inputsplits? If two inputsplits are split, an inputsplit contains a row of incomplete data, will the ER er processing this inputsplit produce i

Hadoop mapreduce jar File Upload When submitting a job, we often execute a command similar to the following: Hadoop jar Wordcount.jar test. WordCount, and then wait for the job to complete to see the results. In the job execution process, the client uploads the jar file into HDFs, then initializes the job by JT and issues the specific task to TT, where we mainly

Original article link Mapreduce has gone through a thorough overhaul in the hadoop-0.23, and now we have a new framework called mapreduce2.0 (mrv2) or yarn. The basic concept of mrv2 is to split two main functions (resource management and Job Scheduling/monitoring) in jobtracker into separate daemon processes. The idea is to have a global resourcemaager (RM) and the applicationmaster (AM) corresponding to

/memory footprint, if two large memory consumption task is dispatched to a piece, it is easy to appear OOM. 4 at the Tasktracker end, the resource is forced to be divided into map task slot and reduce task slot, which can be a waste of resources when only a map task or a reduce task is available, which is the previously mentioned cluster resource benefit Use of the problem. 5 Source code Level analysis, you will find the code is very difficult to read, often because one class did too many thin

, InterruptedException {WordCountMapper mapper = new WordCountMapper();Text value = new Text("hello");org.apache.hadoop.mapreduce.Mapper.Context context = mock(Context.class);mapper.map(null, value, context);verify(context).write(new Text("hello"), new IntWritable(1));}@Testpublic void processResult() throws IOException, InterruptedException {WordCountReducer reducer = new WordCountReducer();Text key = new Text("hello");// {"hello",[1,1,2]}Iterable values = Arrays.asList(new IntWritable(1),new I

Reason:Hadoop-eclipse-plugin-2.7.3.jar compiled JDK versions are inconsistent with the JDK version used by Eclipse startup.Solution One :Modify the Myeclipse.ini file to resolve it. D:/java/myeclipse/common/binary/com.sun.java.jdk.win32.x86_1.6.0.013/jre/bin/client/jvm.dll to: D:/Program Files ( x86)/java/jdk1.7.0_45/jre/bin/client/jvm.dlljdk1.7.0_45 version of the JDK for your own installationIf it is not valid, check that the Hadoop version set in t

Write the WordCount program data as follows:Hello BeijingHello ShanghaiHello ChongqingHello TianjinHello GuangzhouHello Shenzhen...1, Wcmapper:Package com.hadoop.testHadoop;Import java.io.IOException;Import org.apache.hadoop.io.LongWritable;Import Org.apache.hadoop.io.Text;Import Org.apache.hadoop.mapreduce.Mapper;In 4 generics, the first two are the types that specify mapper input data, Keyin is the type of the input key, and Valuein is the type of the input value.The data input and output of m

. getnumreducetasks (); jobcontext context = New Jobcontext (job, jobid ); // Check whether the output directory exists. If yes, an error is returned. Org. Apache. hadoop. mapreduce. outputformat // Create the splits for the job Log. debug (" Creating splits "+ FS. makequalified (submitsplitfile )); Int Maps = writenewsplits (context, submitsplitfile ); /// Determine the split Information Job. Set (" Mapred

Configuring MapReduce>configuration>configuration>Plus this.configuration> property > name>Mapreduce.framework.namename> value>Yarnvalue> Property >configuration>And then configure it inside the yarn-site.xml.configuration> -- property > name>Yarn.resourcemanager.hostnamename> value>Hadoop1value> Property > property > name>Yarn.nodemanager.aux-servicesname> value>Mapreduce_shufflevalue>

overload the protected function, such as issplitable (), which is used to determine whether you can slice a block and return it by default to true, indicating that as long as the data block is larger than the HDFS block size, Then it will be sliced.But sometimes you don't want to slice a file, such as when some binary sequence files cannot be sliced, you need to overload the function to return FALSE. when using Fileinputformat, your primary focus should be on the decomposition of data blocks

Hadoop Reading Notes series article: http://blog.csdn.net/caicongyang/article/category/2166855The role of the 1.MapReduce counter statistics map, reduce, and combiner the number of executions, you can easily judge the code execution Flow 2. MapReduce comes with a counter14/11/26 22:28:51 INFO mapred. JOBCLIENT:COUNTERS:1914/11/26 22:28:51 INFO mapred. Jobclient:f