MapReduce

问题 I am trying to write a mapreduce job where I need to iterate the values twice. So when a numerical csv file is given we need to apply this for each column. For that we need to find the min and max values and apply it in the equation (v1). What I did so far is In map() I emit the column id as key and each column as values In Reduce() I calculated the min and max values of each column. After that I am stuck. Next my aim is to apply the equation (v = [(v − minA)/(maxA − minA)]*(new maxA − new

问题 Does anyone have a good way to run a group function in PHP with a DISTINCT count? The situation is this: I want to check unique logins to our app. This is how the document in the current collection I'm querying looks like: Array ( [_id] => MongoId Object ( [$id] => 50f6da87686ba9f449000003 ) [userId] => 50f6bd0f686ba91a4000000f [action] => login [time] => 1358355079 What I would like to do is count the UNIQUE userIDs through a group statement by date. This is the group statement that I am

问题 My purpose - to launch the demon of namenode. It is necessary for me to work with file system of hdfs, to copy there files from local file system, to create folders in hdfs, and it requires start of the demon of namenode on the port specified in the configuration /conf/core-site.xml file. I launched a script ./hadoop namenode and I received as a result the following messages 2013-02-17 12:29:37,493 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: STARTUP_MSG: /***************************

问题 I am trying to read an auxiliary file in my mapper and here are my codes and commands. mapper code: #!/usr/bin/env python from itertools import combinations from operator import itemgetter import sys storage = {} with open('inputData', 'r') as inputFile: for line in inputFile: first, second = line.split() storage[(first, second)] = 0 for line in sys.stdin: do_something() And here is my command: hadoop jar hadoop-streaming-2.7.1.jar \ -D stream.num.map.output.key.fields=2 \ -D mapred.output

问题 I am currently working on a four node multi cluster. Can anyone suggest me the appropriate block size for working on a 22GB input file? Thanks in advance. Here are my performance results: 64M - 32 min. 128M - 19.4 min 256M - 15 min Now, should I consider making it much larger to 1GB/2GB? Kindly explain if there are any issues if done so. Edit: Also, if the performance increases with increasing block size for a 20GB input file why is the default block size 64MB or 128MB? Kindly answer similar

问题 I am writing a Hadoop scheduler. My scheduling requires finding the CPU time taken by each Map/Reduce task. I know that: The TaskInProgress class maintains the execStartTime and execFinishTime values which are wall-clock times when the process started and finished, but they do not accurately indicate the CPU time consumed by the task. Each task is executed in a new JVM, and I could use the OperatingSystemMXBean.getProcessCpuTime () method, but again the description of the method tells me:

问题 hadoop jar MapReduceTryouts-1.jar invertedindex.simple.MyDriver -D mapreduce.job.reduces=10 /user/notprabhu2/Input/potter/ /user/notprabhu2/output I have been trying in vain to set the number of reducers through the -D option provided by GenericOptionParser but it does not seem to work and I have no idea why. I tried -D mapreduce.job.reduces=10 (with space after -D) and also -Dmapreduce.job.reduces=10 (without space after -D) but nothing seems to dodge. In my Driver class I have implemented

问题 I am learning the HBase. I know how to write a Java program using Hadoop MapReduce and write the output into HDFS; but now I want to write the same output into HBase, instead of HDFS. It should have some similar code like I did before in HDFS thing: context.write(key,value); Could anyone show me an example to achieve this? 回答1: Here's one way to do this: public static class MyMapper extends TableMapper<ImmutableBytesWritable, Put> { public void map(ImmutableBytesWritable row, Result value,

问题 There is an Error as notice below when I ran a MapReduce jar in Centos 6.4 . Hadoop Version is 2.6.0 for 64 bit. The MapReduce failed,how can I solve this? Error: java.lang.RuntimeException: native snappy library not available: this version of libhadoop was built without snappy support. at org.apache.hadoop.io.compress.SnappyCodec.checkNativeCodeLoaded(SnappyCodec.java:64) at org.apache.hadoop.io.compress.SnappyCodec.getCompressorType(SnappyCodec.java:133) at org.apache.hadoop.io.compress

问题 I tried to copy file from local to hdfs. Using the command hadoop dfs -copyFromLocal in/ /user/hduser/hadoop The following error message shown. Please help to find the problem. DEPRECATED: Use of this script to execute hdfs command is deprecated. Instead use the hdfs command for it. 15/02/02 19:22:23 WARN hdfs.DFSClient: DataStreamer Exception org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /user/hduser/hadoop._COPYING_ could only be replicated to 0 nodes instead of