MapReduce

How to set system environment variable from Mapper Hadoop?

由 余生长醉 提交于 2020-01-06 07:52:31
问题 The problem below the line is solved but I am facing another problem. I am doing this : DistributedCache.createSymlink(job.getConfiguration()); DistributedCache.addCacheFile(new URI ("hdfs:/user/hadoop/harsh/libnative1.so"),conf.getConfiguration()); and in the mapper : System.loadLibrary("libnative1.so"); (i also tried System.loadLibrary("libnative1"); System.loadLibrary("native1"); But I am getting this error: java.lang.UnsatisfiedLinkError: no libnative1.so in java.library.path I am totally

Is the input to a Hadoop reduce function complete with regards to its key?

由 让人想犯罪 __ 提交于 2020-01-06 07:17:13
问题 I'm looking at solutions to a problem that involves reading keyed data from more than one file. In a single map step I need all the values for a particular key in the same place at the same time. I see in White's book the discussion about "the shuffle" and am tempted to wonder if when you come out of merging and the input to a reducer is sorted by key, if all the data for a key is there....if you can count on that. The bigger pictures is that I want to do a poor-man's triple-store federation

Is the input to a Hadoop reduce function complete with regards to its key?

由 [亡魂溺海] 提交于 2020-01-06 07:17:07
问题 I'm looking at solutions to a problem that involves reading keyed data from more than one file. In a single map step I need all the values for a particular key in the same place at the same time. I see in White's book the discussion about "the shuffle" and am tempted to wonder if when you come out of merging and the input to a reducer is sorted by key, if all the data for a key is there....if you can count on that. The bigger pictures is that I want to do a poor-man's triple-store federation

Run map reduce for all keys in collections - mongodb

由 会有一股神秘感。 提交于 2020-01-06 03:50:09
问题 i am using map reduce in mongodb to find out the number of orders for a customer like this db.order.mapReduce( function() { emit (this.customer,{count:1}) }, function(key,values){ var sum =0 ; values.forEach( function(value) { sum+=value['count']; } ); return {count:sum}; }, { query:{customer:ObjectId("552623e7e4b0cade517f9714")}, out:"order_total" }).find() which gives me an output like this { "_id" : ObjectId("552623e7e4b0cade517f9714"), "value" : { "count" : 13 } } Currently it is working

Mapper pass values to different mappers-reducers

由 心不动则不痛 提交于 2020-01-05 12:31:27
问题 I have two phases map-reduce hadoop program. (mapper1, reducer1, mapper2, reducer2). Can i pass some of mapper1 key values directly to reducer1 and some others directly to mapper2? 回答1: You could just put have the mapper set key value normally for the ones that you want reducer1 to process, while having the ones that go to mapper2 have some arbitrary key name (lets arbitrarily say "TO_MAPPER_2" in class Text.class). Then your reducer code inside of an if statement so that it only executes

MapReduce-自动化运行配置

由 戏子无情 提交于 2020-01-05 11:04:49
1.打包时指定main Class信息 注意：默认直接通过maven插件打成jar包中没有指定main class信息，因此在运行mapreduce的jar包时必须在指令后明确main class信息 需要在插件进行配置 1 <build> 2 <plugins> 3 <plugin> 4 <groupId>org.apache.maven.plugins</groupId> 5 <artifactId>maven-jar-plugin</artifactId> 6 <configuration> 7 <outputDirectory>${basedir}/target</outputDirectory> 8 <archive> 9 <manifest> 10 <!-- 在打包插件中指定main class 信息 --> 11 <mainClass>com.yt.wordcount.WordCountJob</mainClass> 12 </manifest> 13 </archive> 14 </configuration> 15 </plugin> 16 </plugins> 17 </build> 　　 执行命令：clean package 　　 2.使用wagon插件实现自动上传至hadoop集群 1 <build> 2 <!--扩展maven的插件中加入ssh插件-->

How to share global sequential number generator in Hadoop?

由 [亡魂溺海] 提交于 2020-01-05 09:49:06
问题 Now I am using Hadoop to process the data that will finally be loaded into the same table. I need to a shared sequential number generator to generate id for each row. Now I am using the following approach to generate the unique number: 1) Create a text file, e.g., test.seq, in HDFS for saving the current sequential number. 2) I use a lock file ".lock" to control concurrency. Suppose we have two tasks to processing the data in parallel. If task1 wants to get the number, it will check if the

How to fix this error in hadoop hive vanilla

由 被刻印的时光 ゝ 提交于 2020-01-05 09:35:26
问题 I am facing the following error while executing MapReduce job in Linux(CentOS). I added all the jars in classpath. The database name and table name already in the hive database with some column of data in the table. Then also I can't able to access the data from the hive database table. I'm using vanilla version of hadoop for work. Should i need to edit hive-site.xml file by mysql driver path, username and password for hive?. if yes please tell me the procedure to add username and password

Temporary Collection in MongoDB

由 我怕爱的太早我们不能终老 提交于 2020-01-05 09:07:40
问题 I can't understand this paragraph from mongodb MapReduce documentation (http://docs.mongodb.org/manual/applications/map-reduce/) - what Temporary Collection (optimisation?) is good for (business case, benefits etc)? Temporary Collection The map-reduce operation uses a temporary collection during processing. At completion, the map-reduce operation renames the temporary collection. As a result, you can perform a map-reduce operation periodically with the same target collection name without

CouchDB / Couchbase view ordered by number of keys

由 梦想与她 提交于 2020-01-05 08:03:48
问题 I'm trying to write a view which shows me the top 10 tags used in my system. It's fairly easy to get the amount with _count in the reduce function, but that does not order the list by the numbers. Is there any way to do this? function(doc, meta) { if(doc.type === 'log') { emit(doc.tag, 1); } } _count As a result I'd like to have: Tag3 10 Tag1 7 Tag2 3 ... Instead of Tag1 7 Tag2 3 Tag3 10 Most importantly, I do not want to transfer the full set to my application server and handle it there. 回答1
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