Map-ReduceBig Data, Map-Reduce,

Apache Hadoop

SoftUni TeamTechnical TrainersSoftware Universityhttp://softuni.bg

Map-Reduce

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1. Big Data

2. Map-Reduce What is Map-Reduce?

How It Works?

Mappers and Reducers

Examples

3. Apache Hadoop

Table of Contents

Big DataWhat is Big Data Processing?

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Big data == process very large data sets (terabytes / petabytes) So large or complex, that traditional data processing is inadequate Usually stored and processed by distributed databases Often related to analysis of very large data sets

Typical components of big data systems Distributed databases (like Cassandra, HBase and Hive) Distributed processing frameworks (like Apache Hadoop) Distributed processing systems (like Map-Reduce) Distributed file systems (like HDFS)

Big Data

Map-Reduce

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Map-Reduce is a distributed processing framework Computational model for processing huge data-sets (terabytes) Using parallel processing on large clusters (thousands of nodes) Relying on distributed infrastructure

Like Apache Hadoop or MongoDB cluster

The input and output data is stored in a distributed file system (or distributed database)

The framework takes care of scheduling, executing and monitoring tasks, and re-executes the failed tasks

What is Map-Reduce?

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How map-reduce works?

1. Splits the input data-set into independent chunks

2. Process each chunk by "map" tasks in parallel manner The "map" function groups the input data into key-value pairs Equal keys are processed by the same "reduce" node

3. Outputs of the "map" tasks are Sorted, grouped by key, then sent as input to the "reduce" tasks

4. The "reduce" tasks Aggregate the results per each key and produces the final output

Map-Reduce: How It Works?

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The map-reduce process is a sequence of transformations, executed on several nodes in parallel

Map: groups input chunks of data to key-value pairs E.g. splits documents(id, chunk-content) into words(word, count)

Combine: sorts and combines all values by the same key E.g. produce a list of counts for each word

Reduce: combines (aggregates) all values for certain key

The Map-Reduce Process

(input) <key1, val1> map <key2, val2> combine <key2, list<val2>> reduce <key3, val3> (output)

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We have a very large set of documents (e.g. 200 terabytes) We want to count how many times each word occurs

Input: set of documents {key + content} Mapper:

Extract the words from each document (words are used as keys) Transforms documents {key + content} word-count-pairs {word, count}

Reducer: Sums the counts for each word Transforms {word, list<count>} word-count-pairs {word, count}

Example: Counting Words

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Counting Words: Mapper and Reducer

public void map(Object offset, Text docText, Context context) throws IOException, InterruptedException { String[] words = docText.toString().toLowerCase().split("\\W+"); for (String word : words) context.write(new Text(word), new IntWritable(1));}

public void reduce(Text word, Iterable<IntWritable> counts, Context context) throws IOException, InterruptedException { int sum = 0; for (IntWritable count : counts) sum += count.get(); context.write(word, new IntWritable(sum));}

Word Count in Apache HadoopLive Demo

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We are given a CSV file holding real estate sales data: Estate address, city, ZIP code, state, # beds, # baths, square foots,

sale date price and GPS coordinates (latitude + longitude)

Find all cities that have sales in price range [100 000 … 200 000] As side effect, find the sum of all sales by city

Example: Extract Data from CSV Report

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Process CSV Report – How It Works?

SELECT city, SUM(price)FROM SalesGROUP BY city

chunkingchunking

map mapmap

city sum(price)SACRAMENTO 625140

LINCOLN 843620

RIO LINDA 348500

reduce

reduce

reduce

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Process CSV Report: Mapper and Reducerpublic void map(Object offset, Text inputCSVLine, Context context) throws IOException, InterruptedException { String[] fields = inputCSVLine.toString().split(","); String city = fields[1]; int price = Integer.parseInt(fields[9]); if (price > 100000 && price < 200000) context.write(new Text(city), new LongWritable(price);}public void reduce(Text city, Iterable<LongWritable> prices, Context context) throws IOException, InterruptedException { long sum = 0; for (LongWritable val : prices) sum += val.get(); context.write(city, new LongWritable(sum));}

Processing CSV Reportin Apache Hadoop

Live Demo

Apache HadoopDistributed Processing Framework

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Apache Hadoop project develops open-source software for reliable, scalable, distributed computing Hadoop Distributed File System (HDFS) – a distributed file system that

transparently moves data across Hadoop cluster nodes Hadoop MapReduce – the map-reduce framework HBase – a scalable, distributed database for large tables Hive – SQL-like query for large datasets Pig – a high-level data-flow language for parallel computation

Hadoop is driven by big players like IBM, Microsoft, Facebook, VMware, LinkedIn, Yahoo, Cloudera, Intel, Twitter, Hortonworks, …

Apache Hadoop

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Hadoop Ecosystem

HDFS StorageRedundant (3 copies)For large files – large blocks 64 MB or 128 MB / blockCan scale to 1000s of nodes

MapReduce APIBatch (Job) processingDistributed and localized to clustersAuto-parallelizable for huge amounts of dataFault-tolerant (auto retries)Adds high availability and more

Hadoop LibrariesPigHiveHBase Others

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Hadoop Cluster HDFS (Physical) Storage

Name Node

Data Node 1

Data Node 2

Data Node 3

Secondary Name Node

• Contains web site to view cluster information

• V2 Hadoop uses multiple Name Nodes for HA

One Name Node

• 3 copies of each node by default

Many Data Nodes

• Using common Linux shell commands• Block size is 64 or 128 MB

Work with data in HDFS

Tips: sudo means "run as administrator" (super user) Some distributions use hadoop dfs rather than hadoop fs

Common Hadoop Shell Commands

hadoop fs –cat file:///file2hadoop fs –mkdir /user/hadoop/dir1 /user/hadoop/dir2hadoop fs –copyFromLocal <fromDir> <toDir>hadoop fs –put <localfile> hdfs://nn.example.com/hadoopfilesudo hadoop jar <jarFileName> <method> <fromDir> <toDir> hadoop fs –ls /user/hadoop/dir1hadoop fs –cat hdfs://nn1.example.com/file1hadoop fs –get /user/hadoop/file <localfile>

Hadoop Shell CommandsLive Demo

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Apache Hadoop MapReduce The world's leading implementation of the map-reduce

computational model Provides parallelized (scalable) computing For processing very large data sets Fault tolerant Runs on commodity of hardware

Implemented in many cloud platforms: Amazon EMR, Azure HDInsight, Google Cloud, Cloudera, Rackspace, HP Cloud, …

Hadoop MapReduce

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Hadoop Map-Reduce Pipeline

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Download and install Java and Hadoop http://hadoop.apache.org/releases.html You will need to install Java first

Download a pre-installed Hadoop virtual machine (VM) Hortonworks Sandbox Cloudera QuickStart VM

You can use Hadoop in the cloud / local emulator E.g. Azure HDInsight Emulator

Hadoop: Getting Started

Playing with Apache HadoopLive Demo

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Big data == processing huge datasets that are too big for processing on a single machine Use a cluster of computing nodes

Map-reduce == computational paradigmfor parallel data processing of huge data-sets Data is chunked, then mapped into groups,

then groups are processed and the results are aggregated Highly scalable, can process petabytes of data

Apache Hadoop – industry's leading Map-Reduce framework

Summary

Questions??

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Map-Reduce

https://softuni.bg/trainings/1194/Algorithms-September-2015

License

This course (slides, examples, labs, videos, homework, etc.)is licensed under the "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International" license

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Attribution: this work may contain portions from "Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA license

"Data Structures and Algorithms" course by Telerik Academy under CC-BY-NC-SA license

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