MapReduce

file path in hdfs

由 与世无争的帅哥 提交于 2020-01-01 04:35:08
问题 I want to read the file from the Hadoop File System. In order to achieve the correct path of the file, I need host name and port address of the hdfs . so finally my path of the file will look something like Path path = new Path("hdfs://123.23.12.4344:9000/user/filename.txt") Now I want to know to extract the HostName = "123.23.12.4344" & port: 9000? Basically, I want to access the FileSystem on Amazon EMR but, when I use FileSystem fs = FileSystem.get(getConf()); I get You possibly called

Why do we need Hadoop passwordless ssh?

由 白昼怎懂夜的黑 提交于 2020-01-01 04:10:23
问题 AFAIK, passwordless ssh is needed so that the master node can start the daemon processes on each slave node. Apart from that, is there any use of having passwordless ssh for Hadoop's operation? How are the user code jars and data chunks transferred across the slave nodes? I want to know the mechanism and the protocol used. The passwordless SSH should ONLY be configured for master-slave pairs or even for amongst the slaves? 回答1: You are correct. If ssh is not passwordless, you have to go on

Reverse Sorting Reducer Keys

由 妖精的绣舞 提交于 2020-01-01 03:48:06
问题 What is the best approach to get the Map Output keys to a reducer in reverse order? By default the reducer receives all keys in ascending order of keys. Any help or comments widely appreciated. In simple words, in the normal scenario, if a map emits keys 1,4,3,5,2 the reducer receives the same as 1,2,3,4,5 . I would like the reducer to receive 5,4,3,2,1 instead. 回答1: In Hadoop 1.X, you can specify a custom comparator class for your outputs using JobConf.setOutputKeyComparatorClass. Your

揭秘“撩”大数据的正确姿势：生动示例解说大数据“三驾马车”

由 你说的曾经没有我的故事 提交于 2019-12-31 23:03:00
我是我：“缘起于美丽，相识于邂逅，厮守到白头！” 众听众：“呃，难道今天是要分享如何作诗？！” 我是我：“大家不要误会，今天主要的分享不是如何作诗，而是《揭秘：‘撩’大数据的正确姿势》，下面进入正题。” 话说当下技术圈的朋友，一起聚个会聊个天，如果不会点大数据的知识，感觉都融入不了圈子，为了以后聚会时让你有聊有料，接下来就跟随我的讲述，一起与大数据混个脸熟吧，不过在“撩”大数据之前，还是先揭秘一下研发这些年我们都经历了啥？ 缘起：应用系统架构的从 0 到 1 揭秘：研发这些年我们都经历了啥？ 大道至简。生活在技术圈里，大家静下来想想，无论一个应用系统多庞大、多复杂，无非也就是由一个漂亮的网站门面 + 一个丑陋的管理模块 + 一个闷头干活的定时任务三大板块组成。 我们负责的应用系统当然也不例外，起初设计的时候三大模块绑在一起（All in one），线上跑一个 Tomcat 轻松就搞定，可谓是像极了一个大泥球。 衍化至繁。由于网站模块、管理平台、定时任务三大模块绑定在一起，开发协作会比较麻烦，时不时会有代码合并冲突出现；线上应用升级时，也会导致其它模块暂时不能使用，例如如果修改了一个定时任务的配置，可能会导致网站、管理平台的服务暂时不能用。面对诸多的不便，就不得不对 All in one 的大泥球系统进行拆解。 随着产品需求的快速迭代，网站 WEB 功能逐渐增多

How to build OpenCV with Java under Linux using command line?(Gonna use it in MapReduce)

由 半世苍凉 提交于 2019-12-31 12:59:33
问题 Recently I'm trying OpenCV out for my graduation project. I've had some success under Windows enviroment. And because with Windows package of OpenCV it comes with pre-built libraries, so I don't have to worry about how to build them. But since the project is suppose to run on a cluster with CentOS as host OS for each node, I have to know how to correctly compile, and run these library under Linux enviroment. I've set up a VM with VirtualBox and installed Ubuntu 13.04 on it. But so far I still

How to build OpenCV with Java under Linux using command line?(Gonna use it in MapReduce)

由 萝らか妹 提交于 2019-12-31 12:58:53
问题 Recently I'm trying OpenCV out for my graduation project. I've had some success under Windows enviroment. And because with Windows package of OpenCV it comes with pre-built libraries, so I don't have to worry about how to build them. But since the project is suppose to run on a cluster with CentOS as host OS for each node, I have to know how to correctly compile, and run these library under Linux enviroment. I've set up a VM with VirtualBox and installed Ubuntu 13.04 on it. But so far I still

How to build OpenCV with Java under Linux using command line?(Gonna use it in MapReduce)

由 我怕爱的太早我们不能终老 提交于 2019-12-31 12:58:10
问题 Recently I'm trying OpenCV out for my graduation project. I've had some success under Windows enviroment. And because with Windows package of OpenCV it comes with pre-built libraries, so I don't have to worry about how to build them. But since the project is suppose to run on a cluster with CentOS as host OS for each node, I have to know how to correctly compile, and run these library under Linux enviroment. I've set up a VM with VirtualBox and installed Ubuntu 13.04 on it. But so far I still

MIT6.824 Lab1 MapReduce

由 女生的网名这么多〃 提交于 2019-12-31 11:39:12
MapReduce分布式计算框架 MapReduce是谷歌开发的分布式计算框架。MapReduce需用户指定Map和Reduce两个函数具体操作内容。现实世界大多数计算操作都可以基于该操作完成。 Map&&Reduce操作 Map MapReduce按照记录读取文件，针对每条记录执行Map操作，将记录转化为KeyValues形式保存到中间文件中（根据Key的哈希值映射到指定文件中，文件如何分割根据partition函数） Reduce Reduce 读取中间文件，将相同Key的多个Values合并成到一个Value中。 MapReduce计算框架结构： MapReduce 首先将输入文件划分成M份放入到worker中，每个worker中都有一份代码的副本 其中一份副本作为master，其他worker被master分配工作。设定M个map任务以及R个reduce任务。master选择空闲的worker分配map任务或者reduce任务 分配map任务的worker，将输入文件的内容利用map函数将其解析为key-value，放入到内存中。 与此同时，内存中key-value pair分为R个文件写入到磁盘中。将文件地址传给master。 reduce worker收到文件地址后，利用远程过程调用（RPC）读取所有中间文件，根据key值对文件排序（相同key的pair组成一起）

Custom Map Reduce Program on Hive, what's the Rule? How about input and output?

由 坚强是说给别人听的谎言 提交于 2019-12-31 08:39:32
问题 I got stuck for a few days because I want to create a custom map reduce program based on my query on hive, I found not many examples after googling and I'm still confused about the rule. What is the rule to create my custom mapreduce program, how about the mapper and reducer class? Can anyone provide any solution? I want to develop this program in Java, but I'm still stuck ,and then when formatting output in collector, how do I format the result in mapper and reducer class? Does anybody want

Java MapReduce counting by date

由 橙三吉。 提交于 2019-12-31 07:15:58
问题 I'm new to Hadoop, and i'm trying to do a MapReduce program, to count the max first two occurrencise of lecters by date (grouped by month). So my input is of this kind : 2017-06-01 , A, B, A, C, B, E, F 2017-06-02 , Q, B, Q, F, K, E, F 2017-06-03 , A, B, A, R, T, E, E 2017-07-01 , A, B, A, C, B, E, F 2017-07-05 , A, B, A, G, B, G, G so, i'm expeting as result of this MapReducer program, something like : 2017-06, A:4, E:4 2017-07, A:4, B:4 public class ArrayGiulioTest { public static Logger
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