MapReduce

问题 I have document like the following, I want to use map function to get the latest status with given UserId doc1: _id=id1, UserId='ABC', status='OPEN',... doc2: _id=id2, UserId='BCD', status='OPEN', ..... doc3: _id=id3, UserId='ABC', status='CLOSED'.... For a given userid, if it related two status: open and close, then return that document with close status document For a given userid, if it related just open status, then return that document with open status document doc1: _id=id1, UserId='ABC

问题 getting error while transferring value from one hbase table to other INFO mapreduce.Job: Task Id : attempt_1410946588060_0019_r_000000_2, Status : FAILED Error: java.lang.ClassCastException: org.apache.hadoop.hbase.client.Result cannot be cast to org.apache.hadoop.hbase.client.Mutation at org.apache.hadoop.hbase.mapreduce.TableOutputFormat$TableRecordWriter.write(TableOutputFormat.java:87) at org.apache.hadoop.mapred.ReduceTask$NewTrackingRecordWriter.write(ReduceTask.java:576) at org.apache

问题 var allCollections = db.getCollectionNames(); for (var i = 0; i < allCollections.length; ++i) { var collectioname = allCollections[i]; if (collectioname === 'system.indexes') continue; db.runCommand( { "mapreduce" : collectioname, "map" : function() { for (var key in this) { emit(key, null); } }, "reduce" : function(key, stuff) { return null; }, "out":mongo_test + "_keys" }) } output { "_id" : "_id", "value" : null } { "_id" : "collection_name", "value" : null } { "_id" : "database", "value"

问题 I am doing twitter sentiment analysis using hadoop, flume and hive. while executing the query on hive: SELECT user.screen_name, user.followers_count c from mytweets order by c desc; Shows this error: Query ID = root_20161118234051_f807fa43-4931-41a9-a046-0167b04d80ef Total jobs = 1 Launching Job 1 out of 1 Number of reduce tasks determined at compile time: 1 In order to change the average load for a reducer (in bytes): set hive.exec.reducers.bytes.per.reducer=<number> In order to limit the

问题 I am writing Hadoop seq file using txt as input. I know how to write Sequence file from text file. But i want to limit the output sequence file to some specific size say, 256MB. Is there any inbuilt method to do this? 回答1: AFIAK you'll need to write your own custom output format to limit output file sizes - by default FileOutputFormats create a single output file per reducer. Another option is to create your sequence files as normal, then then a second job (map only), with identity mappers

问题 imagine I have a collection like this: { "_id": "10280", "city": "NEW YORK", "state": "NY", "departments": [ {"departmentType":"01", "departmentHead":"Peter"}, {"departmentType":"02", "departmentHead":"John"} ] }, { "_id": "10281", "city": "LOS ANGELES", "state": "CA", "departments": [ {"departmentType":"02", "departmentHead":"Joan"}, {"departmentType":"03", "departmentHead":"Mary"} ] }, { "_id": "10284", "city": "MIAMI", "state": "FL", "department": [ "departments": [ {"departmentType":"01",

问题 I have installed Cloudera 5.8 in a Linux RHEL 7.2 instance of Amazon EC2. I have logged in with SSH and I am trying to run the wordcount example for testing mapreduce operation with the following command: hadoop jar /opt/cloudera/parcels/CDH-5.8.0-1.cdh5.8.0.p0.42/lib/hadoop-mapreduce/hadoop-mapreduce-examples.jar wordcount archivo.txt output The problem is that the wordcount program is blocked and it not produces the output. Only the following is prompted: 16/08/11 13:10:02 INFO client

问题 The stderr logs the following while running a map-reduce job: root@dbpc42:/tmp/mesos/slaves/20141201-225046-698725789-5050-19765-S24/frameworks/20141201-225046-698725789-5050-19765-0016/executors/executor_Task_Tracker_2/runs/latest# ls hadoop-2.5.0-cdh5.2.0 hadoop-2.5.0-cdh5.2.0.tgz stderr stdout Contents of stderr : WARNING: Logging before InitGoogleLogging() is written to STDERR I1202 19:41:40.323521 7223 fetcher.cpp:76] Fetching URI 'hdfs://dbpc41:9000/hadoop-2.5.0-cdh5.2.0.tgz' I1202 19

问题 I am learning hadoop map reduce using word count example , please see the diagram attached : My questions are regarding how the parallel processing actually happens , my understanding/questions below , please correct me if i am wrong : Split step : This assigns number of mappers , here the two data sets go to two different processor [p1,p2] , so two mappers ? This splitting is done by first processor P. Mapping Step : Each of these processor [p1,p2] now divides the data into key value pairs

问题 This question already has answers here : How do I fix a NoSuchMethodError? (28 answers) Hadoop 2.6.0 Browsing filesystem Java (1 answer) Closed 3 years ago . This is my first experience with Hadoop, and i need help to solve a problem that i am stuck in (as shown in the title). I found an project that i was looking for: https://github.com/tzulitai/distributed-svm Before starting to run a mapReduce Job, i executed those three commands on terminal, as the build info said: $ git clone https:/