hadoop-streaming

I'm getting confused after reading below article on Hadoop- Definitive guide 4th edition(page-204) Before it writes to disk, the thread first divides the data into partitions corresponding to the reducers that they will ultimately be sent to. Within each partition, the background thread performs an in-memory sort by key, and if there is a combiner function, it is run on the output of the sort. Running the combiner function makes for a more compact map output, so there is less data to write to local disk and to transfer to the reducer. Here is my doubt: 1) Who will execute first combiner or

I need to compare a large number of strings similar to 50358c591cef4d76. I have a Hamming distance function (using pHash) I can use. How do I do this efficiently? My pseudocode would be: For each string currentstring= string For each string other than currentstring Calculate Hamming distance I'd like to output the results as a matrix and be able to retrieve values. I'd also like to run it via Hadoop Streaming! Any pointers are gratefully received. Here is what i have tried but it is slow: import glob path = lotsdir + '*.*' files = glob.glob(path) files.sort() setOfFiles = set(files) print len

Installation of hadoop on single node cluster , any idea why do we need to create the following Why do we need SSH access for a new user ..? Why should it be able to connect to its own user account? Why should i specify a password less for a new user ..? When all the nodes are in same machine, why do they are communicating explicitly ..? http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/ Tariq Why do we need SSH access for a new user ..? Because you want to communicate to the user who is running Hadoop daemons. Notice that ssh is actually from a user(on

By default, hadoop map tasks write processed records to files in temporary directory at ${mapred.output.dir}/_temporary/_${taskid} . These files sit here until FileCommiter moves them to ${mapred.output.dir} (after task successfully finishes). I have case where in setup() of map task I need to create files under above provided temporary directory, where I write some process related data used later somewhere else. However, when hadoop tasks are killed, temporary directory is removed from HDFS. Anyone knows if it is possible to tell Hadoop to not delete this directory after task is killed, and

While running a hadoop multi-node cluster , i got below error message on my master logs , can some advise what to do..? do i need to create a new user or can i gave my existing Machine user name over here 2013-07-25 19:41:11,765 WARN org.apache.hadoop.security.UserGroupInformation: No groups available for user webuser 2013-07-25 19:41:11,778 WARN org.apache.hadoop.security.ShellBasedUnixGroupsMapping: got exception trying to get groups for user webuser org.apache.hadoop.util.Shell$ExitCodeException: id: webuser: No such user hdfs-site.xml file <configuration> <property> <name>dfs.replication<

I get "java.lang.IllegalStateException: not ready" in org.bson.BasicBSONDecoder._decode while trying to use MongoDB as input RDD: Configuration conf = new Configuration(); conf.set("mongo.input.uri", "mongodb://127.0.0.1:27017/test.input"); JavaPairRDD<Object, BSONObject> rdd = sc.newAPIHadoopRDD(conf, MongoInputFormat.class, Object.class, BSONObject.class); System.out.println(rdd.count()); The exception I get is: 14/08/06 09:49:57 INFO rdd.NewHadoopRDD: Input split: MongoInputSplit{URI=mongodb://127.0.0.1:27017/test.input, authURI=null, min={ "_id" : { "$oid" : "53df98d7e4b0a67992b31f8d"}},