MapReduce

问题 As suggested here, I am running hadoop in pseudodistributed mode with the following mapred-site.xml file. The job is running on a 4 core machine. <configuration> <property> <name>mapred.job.tracker</name> <value>localhost:9001</value> </property> <property> <name>mapred.map.tasks</name> <value>4</value> </property> <property> <name>mapred.reduce.tasks</name> <value>4</value> </property> </configuration> I am getting the following error: The ratio of reported blocks 1.0000 has reached the

问题 Suppose we had something like the following document, but we wanted to return only the fields that had numeric information: { "_id" : ObjectId("52fac254f40ff600c10e56d4"), "name" : "Mikey", "list" : [ 1, 2, 3, 4, 5 ], "people" : [ "Fred", "Barney", "Wilma", "Betty" ], "status" : false, "created" : ISODate("2014-02-12T00:37:40.534Z"), "views" : 5 } Now I know that we can query for fields that match a certain type by use of the $type operator. But I'm yet to stumble upon a way to $project this

问题 I am working on map reduce program and was thinking about designing computations of the form where a1, b1 are the values associated with a key a1/b1, a1+a2/b1+b2, a1+a2+a3/b1+b2+b3 ... So at every stage of reducer I would require the previous values. How would one design this as a map reduce as at every stage only the values associated with a particular key can be read. If you feel the question is not clear, can you guide me towards this general question? More general question: How would one

问题 I have documents in RavenDb that may look something like this: { "Id": "obj/1", "Version": 1 }, { "Id": "obj/1", "Version": 2 }, { "Id": "obj/1", "Version": 3 }, { "Id": "obj/1", "Version": 4 }, { "Id": "obj/2", "Version": 1 }, { "Id": "obj/2", "Version": 2 }, { "Id": "obj/2", "Version": 3 }, { "Id": "obj/3", "Version": 1 }, { "Id": "obj/3", "Version": 3 } I'm trying to create an index that would give me: The sequences "obj/1" and "obj/2", preferably grouped by Id. Not the sequence "obj/3",

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . I'm familiar and have worked with Hive, Pig, HBase. I have also gone through the Hadoop Definitive guide. I am familiar with core java, MapReduce architecture and MapReduce internals. However, I don't have any hands on experience in MapReduce and I need to learn MapReduce in terms of practical scenarios. Is

问题 I have a Mapper that is going through lots of data and emitting ID numbers as keys with the value of 1. What I hope to accomplish with the MapReduce job is to get a list of all IDs that have been found more than one time across all data, which is a list of duplicate IDs. For example: Mapper emits: abc 1 efg 1 cba 1 abc 1 dhh 1 In this case, you can see that the ID 'abc' has been emitted more than one time by the Mapper. How do I edit this Reducer so that it will only emit the duplicates? i.e.

问题 Is it possible to create a valid *mapreduce*.TaskAttemptID from *mapred*.JobConf ? The background I need to write a FileInputFormatAdapter for an ExistingFileInputFormat . The problem is that the Adapter needs to extend mapred.InputFormat and the Existing format extends mapreduce.InputFormat . I need to build a mapreduce.TaskAttemptContextImpl , so that I can instantiate the ExistingRecordReader . However, I can't create a valid TaskId ...the taskId comes out as null. So How can I get the

问题 i have mongodb 1 collections structure like this- { "_id" : ObjectId("54d34cb314aa06781400081b"), "entity_id" : NumberInt(440), "year" : NumberInt(2011), } { "_id" : ObjectId("54d34cb314aa06781400081e"), "entity_id" : NumberInt(488), "year" : NumberInt(2007), } { "_id" : ObjectId("54d34cb314aa06781400081f"), "entity_id" : NumberInt(488), "year" : NumberInt(2008), } { "_id" : ObjectId("54d34cb314aa067814000820"), "entity_id" : NumberInt(488), "year" : NumberInt(2009), } { "_id" : ObjectId(

问题 To expand on my header in using Hadoop 2.6.. and need to send whole files to my mapper instead of a single line at a time. I have followed Tom Whites code in the Definitive Guide to create WholeFileInputFormat and WholeFileRecordReader but my Mapper is still processing files 1 line at a time. Can anyone see what I'm missing in my code? I used the book example exactly from what I can see. Any guidance will be much appreciated. WholeFileInputFormat.java public class WholeFileInputFormat extends

问题 I am a beginner of MapReduce programming and have coded the following Java program for running in a Hadoop cluster comprising 1 NameNode and 3 DatanNodes : package trial; import java.io.IOException; import java.util.*; import java.lang.Iterable; import org.apache.hadoop.fs.Path; import org.apache.hadoop.conf.*; import org.apache.hadoop.io.*; import org.apache.hadoop.mapred.*; import org.apache.hadoop.util.*; public class Trial { public static class MapA extends MapReduceBase implements Mapper