Getting started with apache-pig

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Remarks

This section provides an overview of what apache-pig is, and why a developer might want to use it.

It should also mention any large subjects within apache-pig, and link out to the related topics. Since the Documentation for apache-pig is new, you may need to create initial versions of those related topics.

Installation or Setup

Linux

Requirements (r0.16.0)

Mandatory

As per current Apache-Pig documentation it supports only Unix & Windows operating systems.

  • Hadoop 0.23.X, 1.X or 2.X
  • Java 1.6 or Later versions installed and JAVA_HOME environment variable set to Java installation directory

Optional

  • Python 2.7 or more (Python UDFs)
  • Ant 1.8 (for builds)

Download the latest Pig release

Download the latest version of pig from http://pig.apache.org/releases.html#Download

Installation

mkdir Pig
cd Downloads/ 
tar zxvf pig-(latest-version).tar.gz 
tar zxvf pig-(latest-version).tar.gz 
mv pig-(latest-version).tar.gz/* /home/Pig/
 

Configuration

After installing Apache Pig, we have to configure it.

Open the .bashrc file

vim ~/.bashrc
 

In the .bashrc file, set the following variables −

export PIG_HOME = /home/Pig
export PATH  = PATH:/home/Pig/bin
 

save the file and reload bashrc again in the environment using

. ~/.bashrc
 

Verifying Pig version

pig –version 
 

If the installation is successful, the above command displays the installed Pig version number.

Testing Pig Installation

pig -h
 

This should display all the possible commands associated with pig

Your pig is now installed locally and you can run it using local parameter like

pig -x local
 

Connecting to Hadoop

If Hadoop1.x or 2.x is Installed on the cluster and the HADOOP_HOME environment variable is setup.

you can connect pig to Hadoop by adding the line in the .bashrc like before

export PIG_CLASSPATH = $HADOOP_HOME/conf
 

Running Pig

Execution Modes

You can run Pig either using the pig (bin/pig) command or by running jar file (java -cp pig.jar)

PIG scripts can be executed in 3 different modes:

  • Local Mode

     pig -x local ...
     
  • Mapreduce Mode (default mode)

     pig -x mapreduce ...
          (or)
     pig ...
     
  • Tez Local Mode

     pig -x tez ...
     

Interactive Mode

Pig can be run in interactive mode using the Grunt shell. Pig Latin statements and commands can be entered interactively in this shell.

Example

$ pig -x <mode> <enter>
grunt>
 

Mode can be one of execution modes as explained in the previous section.

Batch Mode

Pig can also be executed in batch mode. Here a .pig file containing a list of pig statements and commands is provided.

Example

$ pig -x <mode> <script.pig>
grunt>
 

Similarly Mode can be one of execution modes as explained in the previous section.

What Is Pig?

Pig provides an engine for executing data flows in parallel on Hadoop. It includes a language, Pig Latin, for expressing these data flows. Pig Latin includes operators for many of the traditional data operations (join, sort, filter, etc.), as well as the ability for users to develop their own functions for reading, processing, and writing data. Pig is an Apache open source project. This means users are free to download it as source or binary, use it for themselves, contribute to it, and—under the terms of the Apache License—use it in their products and change it as they see fit.

Word Count Example in Pig

Input file

Mary had a little lamb
its fleece was white as snow
and everywhere that Mary went
the lamb was sure to go.
 

Pig Word Count Code

-- Load input from the file named Mary, and call the single
-- field in the record 'line'.
input = load 'mary' as (line);

-- TOKENIZE splits the line into a field for each word.
-- flatten will take the collection of records returned by
-- TOKENIZE and produce a separate record for each one, calling the single
-- field in the record word.
words = foreach input generate flatten(TOKENIZE(line)) as word;

-- Now group them together by each word.
grpd = group words by word;

-- Count them.
cntd = foreach grpd generate group, COUNT(words);

-- Print out the results.
dump cntd;
 

Output

Mary,2
had,1
a,1
little,1
lamb,2
its,1
fleece,1
was,2
white,1
as,1
snow,1
and,1
everywhere,1
that,1
went,1
the,1
sure,1
to,1
go,1
 

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Tuesday, November 22, 2016
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