MapReduce

问题 How to process the Header and Trailer in the file? After processing these lines, it should be removed from the file. The Header line can be found by the offset value 0 and the same trailer the max offset. But the issue here is how we can get both these lines in one mapper? Appreciate your help.. Regards, Mohammed Niaz 回答1: It is possible when we have only one mapper for the given input file. We can process Header and Trailer records in below three options Write a custom InputFormat file and

问题 I wrote a mapper that prints out word pairs and a count of 1 for each of them. import sys from itertools import tee for line in sys.stdin: line = line.strip() words = line.split() def pairs(lst): return zip(lst,lst[1:]+[lst[0]]) for i in pairs(words): print i,1 I tried writing a reducer that creates a dictionary, but I am a bit stuck on how to sum them up. import sys mydict = dict() for line in sys.stdin: (word,cnt) = line.strip().split('\t') #\t mydict[word] = mydict.get(word,0)+1 for word

问题 I am getting OOM exception (Java heap space) for reduce child. In the reducer, I am appending all the values to a StringBuilder which would be the output of the reducer process. The number of values aren't that many. I tried to increase the value of mapred.reduce.child.java.opts to 512M and 1024M but that doesn't help. Reducer code is given below. StringBuilder adjVertexStr = new StringBuilder(); long itcount= 0; while(values.hasNext()) { adjVertexStr.append(values.next().toString()).append("

问题 I'm trying to build a simple Hadoop mapreduce program and I chose Java for that job. I checked out the example codes around and tried to build myself. I created the following gradle script and when I looked at the installed dependencies, none had Mapper or Reducer. Not even org.apache.hadoop.mapreduce package. group 'org.ardilgulez.demoprojects' version '1.0-SNAPSHOT' apply plugin: 'java' repositories { mavenCentral() } dependencies { testCompile group: 'junit', name: 'junit', version: '4.11'

问题 I am beginner of MapReduce programmer. Can you help me design the key-value pairs for the following problem ? Problem statement - Find the maximum value and print it along with the key Input : Key Value ABC 10 TCA 13 RTY 23 FTY 45 The key on the left-hand side column will be unique.No duplicates allowed. Output : FTY 45 Since 45 is the highest of all values, it has to be printed along with the key. Can you help me in designing the map() and reduce() function? What will be the key-value pairs

问题 I am creating a MapReduce simple job. After submitting, its giving below error Suggest to fix this issue 回答1: I know I am too late to answer. But I have noticed that this usually gets solved if you clear your cookies. 来源： https://stackoverflow.com/questions/37207387/hue-500-server-error

问题 I am writing a utility that is a map reduce job where the reducer makes calls to various databases and Hive is one of them. Our cluster is kerberized. I am doing kinit before kicking off the MR job, but when the reducer runs, it fails with an error "No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)" This indicates that it doesnt have a valid ticket. I tried to get a delegation token for Hive service in the MR driver, but it failed because the Hive service

问题 I am having an issue to get the breakdown of the total number of occurrences of words per file. for example, I have four text files (t1, t2, t3, t4). word w1 is twice in file t2, and once in t4, with total occurrences of three. I want to write the same information in output file. I am getting total number of words in each file, but can't get the result i want as above. Here is my map class. import java.io.IOException; import java.util.*; import org.apache.hadoop.io.*; import org.apache.hadoop

问题 I am constantly getting an error "404 not found". I have created cluster and storage account and container. Detailed error that I get is: Unhandled Exception: System.AggregateException: One or more errors occurred. --- Microsoft.WindowsAzure.Storage.StorageException: The remote server returned an error: (404) Not Found. System.Net.WebException: The remote server returned an error: (404) Not Found. This is my code: public static void ConnectToAzureCloudServer() { HadoopJobConfiguration

问题 After playing with MapReduce with MongoDB, The documents look like: {_id: { somecola : 123, somecolb : 456 }, value:10 } I want this format: { _id : somerandomcode, somecola : 123, somecolb : 456, value :10 } Creating a new collection, and foreach + insert can do it but it is too slow, how to do it rapidly? Thanks 来源： https://stackoverflow.com/questions/14574262/how-to-flat-result-after-mongodb-mapreduce