MapReduce

问题 I have taken the Hbase table backup using Hbase Export utility tool . hbase org.apache.hadoop.hbase.mapreduce.Export "FinancialLineItem" "/project/fricadev/ESGTRF/EXPORT" This has kicked in mapreduce and transferred all my table data into Output folder . As per the document the file format will of the ouotput file is sequence file . So i ran below code to extract my key and value from the file . Now i want to run mapreduce to read the key value from the output file but getting below exception

问题 This question already has answers here : How to group an array of objects by key (20 answers) Closed last year . I am using reactJS and have an dynamic array of object from an response which looks like the following: [{ year: 2016, origin: "EN", type: "new" }, { year: 2016, origin: "EN", type: "old" }, { year: 2016, origin: "EN", type: "used" }, { year: 2016, origin: "EN", type: "new" }, { year: 2016, origin: "EN", type: "broken" }, { year: 2016, origin: "EN", type: "used" } ] The dynamic

问题 Reading the syslog generated by Hadoop, I can see lines similar to this one.. 2013-05-06 16:32:45,118 INFO org.apache.hadoop.mapred.JobClient (main): Setting default number of map tasks based on cluster size to : 84 Does anyone know how this value is computed? And how can I get this value in my program? 回答1: I grepped the source code of Hadoop and did not find the string Setting default number of map tasks based on cluster size to at all (whereas I find other strings, which are being printed

问题 What I'm trying to solve is: preserving the order of my array of Ids with $in using this suggested method (mapReduce): Does MongoDB's $in clause guarantee order I've done my homework, and saw it's ideal to convert them to strings: Comparing mongoose _id and strings. Code: var dataIds = [ '57a1152a4d124a4d1ad12d80', '57a115304d124a4d1ad12d81', '5795316dabfaa62383341a79', '5795315aabfaa62383341a76', '57a114d64d124a4d1ad12d7f', '57953165abfaa62383341a78' ]; CollectionSchema.statics.all =

问题 I'm running a hadoop job with mapred.reduce.tasks = 100 (just experimenting). The number of maps spawned are 537 as that depends on the input splits. Problem is the number of reducers "Running" in parallel won't go beyond 4. Even after the maps are 100% complete. Is there a way to increase the number of reducers running as the CPU usage is sub optimal and the Reduce is very slow. I have also set mapred.tasktracker.reduce.tasks.maximum = 100 . But this doesn't seem to affect the numbers of

问题 Can I write output to multiple tables in HBase from my reducer? I went through different blog posts, but ma not able to find a way, even using MultiTableOutputFormat . I referred to this : Write to multiple tables in HBASE But not able to figure out the API signature for context.write call. Reducer code: public class MyReducer extends TableReducer<Text, Result, Put> { private static final Logger logger = Logger.getLogger( MyReducer.class ); @SuppressWarnings( "deprecation" ) @Override

问题 I have an ouput from my mapper: Mapper: KEY, VALUE(Timestamp, someOtherAttrbibutes) My Reducer does recieve: Reducer: KEY, Iterable<VALUE(Timestamp, someOtherAttrbibutes)> I want Iterable<VALUE(Timestamp, someOtherAttrbibutes)> to ordered by Timestamp attribute. Is there any possibility to implement it? I would like to avoid manual sorting inside Reducer code. http://cornercases.wordpress.com/2011/08/18/hadoop-object-reuse-pitfall-all-my-reducer-values-are-the-same/ I'll have to "deep-copy"

问题 I am trying to get some data about the authors of twitter posts, based on the latest data I have Given a collection of twitter posts, I want to pull information from the latest post per author - ie. I want per author to get the friend count. Roughly the collection has data like this. [{"post": {"post_date": "Sat, 24 Mar 2012 05:52:21 +0000" {"author": {"author_id":123, "friend_count":321}} ,{"post_date": "Sat, 17 Mar 2012 03:22:11 +0000" {"author": {"author_id":123, "friend_count":311}} ,{

问题 Good morning, I am new to ZooKeeper and its protocols and I am interested in its broadcast protocol Zab. Could you provide me with a simple java code that uses the Zab protocol of Zookeeper? I have been searching about that but I did not succeed to find a code that shows how can I use Zab. In fact what I need is simple, I have a MapReduce code and I want all the mappers to update a variable (let's say X) whenever they succeed to find a better value of X (i.e. a bigger value). In this case,

问题 I currently have high power (cpu/ram) hosts in the cluster and we are considering to add some good storage but low power hosts. My concern is that it will reduce the jobs performance. Map/Reducers from the new (less powerful) hosts will run slower and the more powerful ones will just have to wait for the result. Is there a way to configure this in Yarn ? Maybe to set a priority for the hosts or to assign mapper/reducers according to the number of cores on each machines. Thanks, Horatiu 回答1: