hadoop fundamentals

Read files For more information about the file reading mechanism, see: The client calls the open () method of the filesystem object (corresponding to the HDFS file system, and calls the distributedfilesystem object) to open the file (that is, the first step in the figure ), distributedfilesystem uses Remote Procedure Call to call namenode to obtain the location of the first several blocks of the file (step 2 ). For each block, namenode returns the address information of all namenode that owns t

in the Hadoop Eclipse Development Environment Building In this article, the 15th.) mentions permission-related exceptions, as follows:15/01/30 10:08:17 WARN util. nativecodeloader:unable to load Native-hadoop library for your platform ... using Builtin-java classes where applicable15/ 01/30 10:08:17 ERROR Security. Usergroupinformation:priviledgedactionexception As:zhangchao3 cause:java.io.IOException:Faile

the query statement has syntax, it is also necessary to do syntax analysis, grammar analysis and language processing.1. Lexical analysis is mainly used to identify words and keywords.In the above example, after lexical analysis, the word has lucene,learned,hadoop, the key word has and, not.If an illegal keyword is found in the lexical analysis, an error occurs. such as Lucene AMD learned, where due to and misspelled, led to AMD as a common word to pa

. This function is used to map the intermediate key-value pairs produced by the map function to a partition, and the simplest implementation is to hash the keys and then modulo the R. A compare function. This function is used to sort the reduce job, which defines the key size relationship. An output writer. Responsible for writing the results to the underlying distributed file system. A combiner function. The actual is the reduce function, which is used for the optimization mentioned

Detailed procedures for starting the HDFS process using start-dfs.sh The scripts involved are: Under Bin: hadoop-config.sh start-dfs.sh hadoop-daemons.sh slaves.sh hadoop-daemon.sh Hadoop Conf under: hadoop-env.sh Where both

Preface The most interesting thing about hadoop is hadoop Job Scheduling. Before introducing how to set up hadoop, it is necessary to have a deep understanding of hadoop job scheduling. We may not be able to use hadoop, but if we understand the Distributed Scheduling Princip

Hadoop distributed platform optimization, hadoop Hadoop performance tuning is not only its own tuning, but also the underlying hardware and operating system. Next we will introduce them one by one: 1. underlying hardware Hadoop adopts the master/slave architecture. The master (resourcemanager or namenode) needs to mai

OneEclipse Import Hadoop Source projectBasic steps:1) Create a new Java project "hadoop-1.2.1" in Eclipse2) Copy the Core,hdfs,mapred,tools,example four directory under the directory src of the Hadoop compression package to the SRC directory of the new project above3) Right click to select Build path, modify Java Build path "source", delete src, add src/core,src/

In Hadoop, data processing is resolved through the MapReduce job. Jobs consist of basic configuration information, such as the path of input files and output folders, which perform a series of tasks by the MapReduce layer of Hadoop. These tasks are responsible for first performing the map and reduce functions to convert the input data to the output results. To illustrate how MapReduce works, consider a simp

A virtual machine was started on Shanda cloud. The default user is root. An error occurred while running hadoop: [Error description] Root @ snda:/data/soft/hadoop-0.20.203.0 # bin/hadoop FS-put conf Input11/08/03 09:58:33 warn HDFS. dfsclient: datastreamer exception: Org. apache. hadoop. IPC. remoteException: Java. io.

Hadoop provides mapreduce with an API that allows you to write map and reduce functions in languages other than Java: hadoop streaming uses standard streamams) as an interface for data transmission between hadoop and applications. Therefore, you can write the map and reduce functions in any language, as long as it can read data from the standard input stream (std

Apache Hadoop and the Hadoop EcosystemHadoop is a distributed system infrastructure developed by the Apache Foundation .The user is able to understand the distributed underlying details. Develop distributed programs. Take advantage of the power of the cluster for fast operations and storage.Hadoop implements a distributed filesystem (Hadoop distributedFile system

Whether you are adding machines and removing machines in a Hadoop cluster, there is no downtime and the entire service is uninterrupted. Before this operation, the cluster of Hadoop is as follows: The machine condition for HDFs is as follows: The machine condition of Mr is as follows: Adding Machines In the master machine of the cluster, modify the $hadoop_home/conf/slaves file to add the hostname of the n

Inkfish original, do not reprint commercial nature, reproduced please indicate the source (http://blog.csdn.net/inkfish). Hadoop is an open source cloud computing platform project under the Apache Foundation. Currently the latest version is Hadoop 0.20.1. The following is a blueprint for Hadoop 0.20.1, which describes how to install

Currently in Hadoop used more than lzo,gzip,snappy,bzip2 these 4 kinds of compression format, the author based on practical experience to introduce the advantages and disadvantages of these 4 compression formats and application scenarios, so that we in practice according to the actual situation to choose different compression format. 1 gzip compression Advantages: The compression ratio is high, and the compression/decompression speed is relatively fas

to facilitate the MapReduce direct access to the relational database (mysql,oracle). Hadoop offers two classes of Dbinputformat and Dboutputformat. Through the Dbinputformat class, the database table data is read into HDFs, and the result set generated by MapReduce is imported into the database table according to the Dboutputformat class.error when executing mapreduce: java.io.IOException:com.mysql.jdbc.Driver, usually because the program cannot find

First, compile the Hadoop pluginFirst you need to compile the Hadoop plugin: Hadoop-eclipse-plugin-2.6.0.jar Before you can install it. Third-party compilation tutorial: Https://github.com/winghc/hadoop2x-eclipse-pluginIi. placing plugins and restarting eclipsePut the compiled plugin Hadoop-eclipse-plugin-2.6.0.jar int

Make sure that the three machines have the same user name and install the same directory *************SSH Non-key login simple introduction (before building a local pseudo-distributed, it is generated, now the three machines of the public key private key is the same, so the following is not configured)Stand-alone operation:Generate Key: Command ssh-keygen-t RSA then four carriage returnCopy the key to native: command Ssh-copy-id hadoop-senior.zuoyan.c

1, the main learning of Hadoop in the four framework: HDFs, MapReduce, Hive, HBase. These four frameworks are the most core of Hadoop, the most difficult to learn, but also the most widely used.2, familiar with the basic knowledge of Hadoop and the required knowledge such as Java Foundation,Linux Environment, Linux common commands 3. Some basic knowledge of Hadoo

Using HDFS to store small files is not economical, because each file is stored in a block, and the metadata of each block is stored in the namenode memory. Therefore, a large number of small files, it will eat a lot of namenode memory. (Note: A small file occupies one block, but the size of this block is not a set value. For example, each block is set to 128 MB, but a 1 MB file exists in a block, the actual size of datanode hard disk is 1 m, not 128 M. Therefore, the non-economic nature here ref