CONTENTSWHAT IS HADOOPHADOOP APPROACHSUB PROJECTS OF HADOOP MAPREDUCE HDFSCASE STUDY USING HADOOPAPPLICATION AREA OF HADOOP
WHAT IS HADOOP It is a open source software framework which support data intensive distributed application. It enables us to explore complex data,using custom analysis tailored to our information and question. It is helpful in unstructured and semistructured data analysis.
HADOOP APPROACH The hadoop works in two phase. First phase is Data Distribution. Second phase is Map reduce:Isolated Process. Data Distribution:- in Data Distribution phase data is loaded to all the nodes of the clusters as it is being loaded.The HDFS will split large data files into chunks managed by different clusters.In addition,data is replicated to across many sites so that single failure will Not result in data unavailable.
DATA DISTRIBUTION PROCESSData replicated across different sites, form a common namespace so they are Universally accessible.
DATA DISTRIBUTION PHASE CONTD…Individual input files are broken into lines or other format specific to the Application Logic.Each process running on a node in the cluster then processes a subset of these Records.The hadoop framework then schedules these processes in proximity to the location of data/records,most data is read from the local disk straight into the cpu,preventing Unnecessary network transfers.this strategy of moving computation to data,instead of moving the data to computation allows Hadoop to achieve high performance.
MAP REDUCE: ISOLATION PROCESSHadoop limits the amount of communication as each individual record is processed by a task in isolation from one another.Records are processed in isolation by tasks called Mappers.Output from different mappers is brought into second list called as Reducers.The advantage of having isolated task processing is that no user level message exchange nor do nodes need rollback to pre-arranged checkpoints.
SUB PROJECTS OF HADOOP MAPREDUCE HDFS HIVE CHUKWA CORE HBASE AVRO
WHAT IS MAPREDUCE? MapReduce is a programming model used for processing large data sets. Programs written in this functional style are automatically parallelized and executed on a large cluster of commodity machines. MapReduce is an associated implementation for processing and generating large data sets.
THE PROGRAMMING MODEL OF MAPREDUCEMap, written by the user, produces a set of intermediatekey/value pairs. TheMapReduce library groups together all intermediate values associated with thesame intermediate key I and passes them to the Reduce function .
The Programming Model Of MapReduce Contd…The Reduce function, also written by the user, accepts an intermediate key Iand a set of values for that key. It merges together these values to form apossibly smaller set of values.
Example of programming model:-Let Map(k,v)=emit(k.toupper(),v.toupper());Map(foo,bar).FOO,BAR ,Map(ask,cat)-> ASK,CATlet reduce(k, vals)sum = 0foreach int v in vals:sum += vemit(k, sum)(“a”, [42, 100, 312]) --> (“A”, 454)(“b”, [12, 6, -2]) --> (“B”, 16)
BENEFITS OF PROGRAMING MODELPrograms written in this functional style are automatically parallelized and executed on a large cluster of commodity machines.The run time system (Hadoop framework) takes care of the details of partitioning the input data,scheduling the programme execution,handling machine failures.This allows programmers without any experience inparallel and distributed systems to easily utilize the resources of a large distributed system.
MAPREDUCE WORKING A MapReduce job is a unit of work that the client wants to be performed: it consists of the input data, the MapReduce program and configuration information. Hadoop runs the job by dividing it into tasks, of which there are two types: map tasks and reduce tasks . There are two types of nodes that control the job execution process: tasktrackers and jobtrackers . The jobtracker coordinates all the jobs run on the system by scheduling tasks to run on tasktrackers. Tasktrackers run tasks and send progress reports to the jobtracker, which keeps a record of the overall progress of each job. If a tasks fails, the jobtracker can reschedule it on a different tasktracker.
MapReduce Working Contd… Input splits: Hadoop divides the input to a MapReduce job into fixed- size pieces called input splits or just splits. Hadoop creates one map task for each split, which runs the user-defined map function for each record in the split. The quality of the load balancing increases as the splits become more fine-grained. But if splits are too small, then the overhead of managing the splits and of map task creation begins to dominate the total job execution time. For most jobs, a good split size tends to be the size of a HDFS block, 64 MB by default.
INPUT TO REDUCE TASKS Reduce tasks don’t have the advantage of data locality—the input to a single reduce task is normally the output from all mappers. Input for reduce task can be of single input,multiple input. For some application there is no need of reduce function,in that case output from map function is directly stored in hdfs.MapReduce data flow with a single reduce task
MapReduce data flow with multiple reduce tasksMapReduce data flow with no reduce tasks
COMBINER FUNCTION•Many MapReduce jobs are limited by the bandwidth available on the cluster.•In order to minimize the data transferred between the map and reduce tasks, combiner functions are introduced.•Hadoop allows the user to specify a combiner function to be run on the map output—the combiner function’s output forms the input to the reduce function.•Combiner finctions can help cut down the amount of data shuffled betweenthe maps and the reduces.
HADOOP MAPREDUCE UTILITYHADOOP STREAMING HADOOP PIPESHadoop provides an API to Hadoop Pipes is the name of TheMapReduce that allows the C++ interface to Hadoopuser to write their map and MapReduce.reduce functions inlanguages other than Java.Hadoop Streaming uses Unlike Streaming, which usesUnix standard streams as standard input and output tothe interface between communicate with the map andHadoop and your program, reduce code, Pipes uses socketsso you can use any language as the channel over which thethat can read standard input tasktracker communicates withand write to standard output the process running the C++ mapto write your MapReduce or reduce function. JNI is notprogram. used.
HADOOP DISTRIBUTEDFILESYSTEM (HDFS) Filesystems that manage the storage across a network of machines are called distributed filesystems. Hadoop comes with a distributed filesystem called HDFS, which stands for Hadoop Distributed Filesystem. HDFS, the Hadoop Distributed File System, is a distributed file system designed to hold very large amounts of data (terabytes or even petabytes) and provide high-throughput access to the information. HDFS make our filesystem tolerate to node failure without suffering data loss.
GOALS OF HDFSMaking distributed filesystems is more complex than regular disk filesystems. Thisis because the data is spanned over multiple nodes, so all the complications ofnetwork programming kick in. •Hardware Failure• An HDFS instance may consist of hundreds or thousands of server machines, each storing part of the file system’s data.•The fact that there are a huge number of components and that each component has a non-trivial probability of failure means that some component of HDFS is always non-functional.•Therefore, detection of faults and quick, automatic recovery from them is a core architectural goal of HDFS. •Large Data Sets• Applications that run on HDFS have large data sets. A typical file in HDFS is gigabytes to terabytes in size. Thus, HDFS is tuned to support large files.• It should provide high aggregate data bandwidth and scale to hundreds of nodes in a single cluster.
GOALS OF HDFS Streaming Data Access• Applications that run on HDFS need streaming access to their data sets.• They are not general purpose applications that typically run on general purpose file systems.• HDFS is designed more for batch processing rather than interactive use by users. The emphasis is on high throughput of data access rather than low latency of data access. Simple Coherency Model• HDFS applications need a write-once-read-many access model for files.• A file once created, written, and closed need not be changed.• This assumption simplifies data coherency issues and enables high throughput data access.• A Map/Reduce application or a web crawler application fits perfectly with this model.• There is a plan to support appending-writes to files in the future.
Goals of HDFS Portability Across Heterogeneous Hardware and Software Platforms HDFS has been designed to be easily portable from one platform to another. This facilitates widespread adoption of HDFS as a platform of choice for a large set of applications. Moving Computation is cheaper than Moving Data. A computation request is much more efficient if it is executed near the data it operates on. This minimizes network congestion and increase the overall throughput of the system. HDFS provides interfaces for applications to move themselves closer to where data is located.
HDFS CONCEPT Blocks:• A block is the minimum amount of data that can be read or written 64 MB by default.• Files in HDFS are broken into block-sized chunks, which are stored as independent units.• HDFS blocks are large compared to disk blocks and the reason is to minimize the cost of seeks. By making a block large enough, the time to transfer the data from the disk can be made to be significantly larger than the time to seek to the start of the block. Thus the time to transfer a large file made of multiple blocks operates at the disk transfer rate.
BENEFITS OF BLOCKABSTRACTION A file can be larger than any single disk in the network. There’s nothing that requires the blocks from a file to be stored on the same disk, so they can take advantage of any of the disks in the cluster. Making the unit of abstraction a block rather than a file simplifies the storage subsystem. Blocks provide fault tolerance and availability. To insure against corrupted blocks and disk and machine failure, each block is replicated to a small number of physically separate machines (typically three). If a block becomes unavailable, a copy can be read from another location in a way that is transparent to the client.
NAMENODES AND DATANODES A HDFS cluster has two types of node operating in a master-worker pattern: a namenode (the master) and a number of datanodes (workers). The namenode manages the filesystem namespace. It maintains the filesystem tree and the metadata for all the files and directories in the tree. Datanodes are the work horses of the filesystem. They store and retrieve blocks when they are told to (by clients or the namenode) and they report back to the namenode periodically with lists of blocks that they are storing. Without the namenode, the filesystem cannot be used. In fact, if the machine running the namenode were obliterated, all the files on the filesystem would be lost since there would be no way of knowing how to reconstruct the files from the blocks on the datanodes.
NAMENODE & DATANODES
SECONDARY NAMENODE CONCEPT To make the namenode resilient to failure, Hadoop provides two mechanisms for this: 1.To back up the files that make up the persistent state of the filesystem metadata. Hadoop can be configured so that the namenode writes its persistent state to multiple filesystems.2. Another solution is to run a secondary namenode. The secondary namenode usually runs on a separate physical machine, since it requires plenty of CPU and as much memory as the namenode to perform the merge. It keeps a copy of the merged namespace image, which can be used in the event of the namenode failing.
HDFS READ OPEARTION
HDFS WRITE OPEARTION
FILE SYSTEM NAMESPACE HDFS supports a traditional hierarchical file organization. A user or an application can create and remove files, move a file from one directory to another, rename a file, create directories and store files inside these directories. HDFS does not yet implement user quotas or acces permissions. HDFS does not support hard links or soft links. However, the HDFS architecture does not preclude implementing these features. The Namenode maintains the file system namespace. Any change to the file system namespace or its properties is recorded by the Namenode. An application can specify the number of replicas of a file that should be maintained by HDFS. The number of copies of a file is called the replication factor of that file. This information is stored by the Namenode..
DATA REPLICATION The blocks of a file are replicated for fault tolerance. The NameNode makes all decisions regarding replication of blocks. It periodically receives a Heartbeat and a Blockreport from each of the DataNodes in the cluster. Receipt of a Heartbeat implies that the DataNode is functioning properly. A Blockreport contains a list of all blocks on a DataNode. When the replication factor is three, HDFS’s placement policy is to put one replica on one node in the local rack, another on a different node in the local rack, and the last on a different node in a different rack.
MAIN FEATURES OF HDFS Cluster Rebalancing• It automatically move data from one Data node to another if the free space on a data node falls below a certain threshhold.• In case of sudden dynamic demand ,it dynamically create additional replicas and rebalance other data in the clusters. Data Integrity• It is possible that block of data fetched from the datanode arrives is corrupted due to fault in storage space,network faults or buggy softwares.• When client creates HDFS file, it computes checksum of each block in file and store that in separate hidden file in the same HDFS namespace.• When client retrieves file contents it verifies the data it received by computing checksum. Robustness from namenode failure,datanode failure and network partition
HADOOP ARCHIVES HDFS stores small files inefficiently, since each file is stored in a block, and block metadata is held in memory by the namenode. Thus, a large number of small files can eat up a lot of memory on the namenode. Hadoop Archives or HAR files are a file archiving facility that packs files into HDFS blocks more efficiently, thereby reducing namenode memory usage while still allowing transparent access to files. Hadoop Archives can be used as input to MapReduce. Archives are immutable once they have been created. To add or remove files, you must recreate the archive.
LIMITATIONS OF HDFS Low-latency data access Applications that require low-latency access to data, in the tens of milliseconds range, will not work well with HDFS.Remember HDFS is optimized for delivering a high throughput of data, and this may be at the expense of latency. HBase is currently a better choice for low- latency access. Multiple write modification siters, arbitrary file Files in HDFS may be written to by a single writer. Writes are always made at the end of the file. There is no support for multiple writers, or for modifications at arbitrary offsets in the file.
FILE STRUCTURE SUPPORTED BYHADOOPNAME EXTENSION DESCRIPTIONHFTP Hdfs.hftpfilesystem Providing read-only access to hdfs over http.HDFS Hdfs.DistributedFilesys HDFS is designed to tem work efficiently in conjuction with Mapreduce.Local Fs.localfilesystem A filesystem for a locally connected disk with client side checksumKFS(cloud store) Fs.kfs.kosmos. Cloudstore is a Filesystem distributed file system like hdfs or GFS.
NAME EXTENSION DESCRIPTIONHSFTP Hdfs.hsftpfilesystem A filesystem providing read-only access to HDFS over HTTPS.HAR Fs.harfilesystem A filesystem layered on another filesystem for archiving files.FTP Fs.ftp.Ftpfilesystem A filesystem backed by an FTP server.S3(BLOCK BASE) Fs.s3.S3FilesystemA A filesystem backed by amazon s3,which stores files in blocks to overcome s3 limitation.
COMPARISION OF HADOOP WITH RDBMS Hadoop uses a brute force method whereas rdbms have optimization methods for accessing data such as indexes . TRADITIONAL MAP REDUCE RDBMSData size Gigabytes PetabytesAccess Interactive,batch BatchUpdates Read,write many Write once,read many TimesStructure Static scheme Dynamic schemaIntegrity High LowScaling Non linear linear
CASE STUDY OF SCIENTIFIC DATAPROCESSING ON A CLOUD USINGHADOOPDESCRIPTION• Our goal is to study the complex molecular interaction that regulate biological systems.• We have to develop an imaging platform to acquire and analyze live cell data.• The platform has the capability to record data in highthrough put and efficiently analysis the data.
DESCRIPTION CONTD... The acquistion system has a data rate of 1.5 MBps, and a typical 48 hours experiment can generate more than 260 GB of images. The data analysis task for this platform is daunting:thousands of cells in the video need to be tracked and characterized individually. Image analysis is the current bottleneck in our data processing pipieline,to solve it we use parallelization. To gather such a large info,storing them into different nodes and perform analysis on it we use hadoop framework. We use local eight core server for data processing.
SYSTEM DESIGNHadoop component used for building such aplatform are: 1. The map-reduce programming and execution enviornment. 2. The reliable distributed file system called DFS. 3. A bigTable-like storage system for sparsely structured data called Hbase.
PROGRAMMING MAP-REDUCE It handles the way input data is split into parts for processing Mapreduce,how it handles the way input data formats and how it handles the extraction of atomic data records from the split file. This approach is implemented by writing new classes that implement the Hadoop interfaces for handling input and input splits. We have implemented the following classes: StringArrayInputFormat.java (implements Hadoops InputFormat interface). CommaSeparatedStringInputSplitRecordReader.java (implements Hadoops RecordReader interface).
HADOOP DFS Hadoops DFS is a flat-structure distributed file system. Its master node is called namenode and slave nodes are called datanodes. Namenode is visible to all cloud nodes and provides a uniform global view for file paths in a traditional hierarchical structure. File contents are not stored hierarchically, but are divided into low level data chunks and stored in datanodes with replication. Data chunk pointers for files are linked to their corresponding locations by namenode.
HBASE TABLE HBase is a BigTable like data store. It also employs a masterslave topology, where its master maintains a table-like view for users. The data stored in HBase are sorted key-value pairs logically organized as sparstables indexed by row keys with corresponding column family values. Each column family represents one or more nested key-value pairs that are grouped together with the same column family as key prefix.
TASK PERFORMED BYSYSTEM The client can issues three types of simple request to cloud application: a request for transfering experiment data,a request for performing an analysis job on a certain acquistion,a request for querying/viewing analysis results. For request of submission or query,it inserts a record into the analysis table in Hbase.
ADVANTAGES OF USING HBASE DFS provides reliable storage, and current database systems cannot make use of DFS directly. Therefore, HBase may have a better degree of fault tolerance for large-scale data management in some sense. We find it natural and convenient to model our data using sparse tables because we have varying numbers of fields with different metadata, and the table organization can change signicantly as the usage of the system is extended to new analysis programs and new types of input or output data.
COMPARISION OF HADOOP AND NON HADOOP APPROACHHADOOP NON HADOOPHadoops MapReduce. MapReduceHadoops Distributed File System Google File System (GFS).(DFS).The HBase storage system for sparse BigTable, a scalable and reliablestructured data. distributed storage system for sparse structured data.
APPLICATION AREA OFHADOOPSome of the key areas of distributed computingwhere hadoop run them efficiently are:- Mobile data E-commerce Energy discovery Energy saving Infrastructure management Image processing Online travelling booking
REFERENCES J.Dean and S.Ghemawat.‘‘MapReduce:Simplified Data Processing on large clusters”,Communication of the ACM,S1(1),Pages 107-113,2009 . K.Kim,k.Joen,H.Han,G.Kim.‘‘Mrbench: A Benchmark for Mapreduce Framework”:In . procedings of the 2010 14th IEEE International Conference on parallel and distributed system,Pages 11-18,2010. http://developer.yahoo.com/Hadoop/tutorial/module5.html. Atterburg.G,Bardnovrki.A,Burm.k,Rana. ‘‘A.Hadoop distributed file system for the grid”,IEEE,Pages 1056-1061,2009. Shvachko.k,Hairong kuang,Radia: ‘‘The Distributed File system” ,Communication of the ACM,Pages 1-10,2010. http://hadoop.apache.org/architecture-hdfs. CheZhn ang,Hans De Sterck,Ashraf Aboulnaga and Rob Sladek:Case Study of Scientific Data Processing on a Cloud Using Hadoop. Tao Fei, Zhang Lin, Guo Hua, Luo Yongliang, Ren Lei, “Typical characteristics of cloud manufacturing and several key issues of cloud service composition,” IEEE vol. 17, pp. 477–486, Mar 2011.