MapReduce | 易学教程

mapreduce参数优化

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mapreduce 参数(重要配置参数)优化资源相关参数以下参数是在用户自己的mr应用程序中配置就可以生效 mapreduce.map.memory.mb : 一个 Map Task 可使用的资源上限（单位: MB ），默认为 1024 。如果 Map Task 实际使用的资源量超过该值，则会被强制杀死。 mapreduce.reduce.memory.mb : 一个 Reduce Task 可使用的资源上限（单位: MB ），默认为 1024 。如果 Reduce Task 实际使用的资源量超过该值，则会被强制杀死。 mapreduce.map.java.opts : Map Task 的 JVM 参数，你可以在此配置默认的 java heap size 等参数 -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc （ @taskid@ 会被 Hadoop 框架自动换为相应的 taskid ）, 默认值: '' mapreduce.reduce.java.opt s: Reduce Task 的 JVM 参数，你可以在此配置默认的 java heap size 等参数 -Xmx1024m -verbose:gc -Xloggc:/tmp/@taskid@.gc , 默认值: '' mapreduce.map.cpu.vcores :

Mongo User Defined Functions and Map Reduce

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问题 Is there a way in mongo to create user-defined Javascript functions. I have several Map/Reduce functions on the client side that i would like to use within other MR functions. For example, several MR functions calculate all sorts of averages. I want to be able to use them like so : function reduce(k,v) { if (val > myDatabaseAverage()) // ..do something } 回答1: Use db.system.js.save( { _id : "myDatabaseAverage" , value : function(){ // ..do something } } ); That will store the JS function on

Spark on yarn jar upload problems

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问题 I am trying to run a simple Map/Reduce java program using spark over yarn (Cloudera Hadoop 5.2 on CentOS). I have tried this 2 different ways. The first way is the following: YARN_CONF_DIR=/usr/lib/hadoop-yarn/etc/hadoop/; /var/tmp/spark/spark-1.4.0-bin-hadoop2.4/bin/spark-submit --class MRContainer --master yarn-cluster --jars /var/tmp/spark/spark-1.4.0-bin-hadoop2.4/lib/spark-assembly-1.4.0-hadoop2.4.0.jar simplemr.jar This method gives the following error: diagnostics: Application

How to sort comma separated keys in Reducer ouput?

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问题 I am running an RFM Analysis program using MapReduce. The OutputKeyClass is Text.class and I am emitting comma separated R (Recency), F (Frequency), M (Monetory) as the key from Reducer where R=BigInteger, F=Binteger, M=BigDecimal and the value is also a Text representing Customer_ID. I know that Hadoop sorts output based on keys but my final result is a bit wierd. I want the output keys to be sorted by R first, then F and then M. But I am getting the following output sort order for unknown

How to do unit testing of custom RecordReader and InputFormat classes?

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问题 I have developed one map-reduce program. I have written custom RecordReader and InputFormat classes. I am using MR Unit and Mockito for unit testing of mapper and reducer. I would like to know how to unit test custom RecordReader and InputFormat classes? What is the most preferred way to test these classes? 回答1: thanks to user7610 compiled and somewhat tested version of the example code from the answer import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.fs.Path; import org

Key of object type in the hadoop mapper

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问题 New to hadoop and trying to understand the mapreduce wordcount example code from here. The mapper from documentation is - Mapper<KEYIN,VALUEIN,KEYOUT,VALUEOUT> I see that in the mapreduce word count example the map code is as follows public void map(Object key, Text value, Context context) Question - What is the point of this key of type Object? If the input to a mapper is a text document I am assuming the value in would be the chunk of text (64MB or 128MB) that hadoop has partitioned and

Hadoop multiple inputs

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问题 I am using hadoop map reduce and I want to compute two files. My first Map/Reduce iteration is giving me an a file with a pair ID number like this: A 30 D 20 My goal is to use that ID from the file to associate with another file and have another output with a trio: ID, Number, Name, like this: A ABC 30 D EFGH 20 But I am not sure whether using Map Reduce is the best way to do this. Would it be better for example to use a File Reader to Read the second input file and get the Name by ID? Or can

Map reduce job getting stuck at map 0% reduce 0%

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问题 I am running the famous wordcount example. I have a local and prod hadoop setup. The same example is working in prod, but its not working locally. Can someone tell me what should I look for. The job is getting stuck. The task logs are: ~/tmp$ hadoop jar wordcount.jar WordCount /testhistory /outputtest/test Warning: $HADOOP_HOME is deprecated. 13/08/29 16:12:34 WARN mapred.JobClient: Use GenericOptionsParser for parsing the arguments. Applications should implement Tool for the same. 13/08/29

How to get print output for debugging map/reduce in Mongoid?

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问题 I'm writing a map/reduce operation with Mongoid 3.0. I'm trying to use the print statement to debug the JS functions. This is a troubleshooting suggestion from the MongoDB docs, e.g.: reduce = %Q{ function(user_id, timestamps) { var max = 0; timestamps.forEach(function(t) { var diff = t.started_at - t.attempted_at; if (diff > max) { max = diff; } }); print(user_id + ', ' + max); return max; }; } MyCollection.all.map_reduce(map, reduce).to_a Unfortunately the output from the print statement

CouchDB Views: remove duplicates and order by time

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问题 Based on a great answer to my previous question, I've partially solved a problem I'm having with CouchDB. This resulted in a new view. Now, the next thing I need to do is remove duplicates from this view while ordering by date. For example, here is how I might query that view: GET http://scoates-test.couchone.com/follow/_design/asset/_view/by_userid_following?endkey=[%22c988a29740241c7d20fc7974be05ec54%22]&startkey=[%22c988a29740241c7d20fc7974be05ec54%22,{}]&descending=true&limit=3 Resulting