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The Pig tutorial shows you how to run two Pig scripts in local mode and hadoop mode.

  • Local Mode: To run the scripts in local mode, no Hadoop or HDFS installation is required. All files are installed and run from your local host and file system.
  • Hadoop Mode: To run the scripts in hadoop (mapreduce) mode, you need access to a Hadoop cluster and HDFS installation.

The Pig tutorial file (pigtutorial.tar.gz) or the tutorial/pigtutorial.tar.gz file in the pig distribution) includes the Pig JAR file (pig.jar) and the tutorial files (tutorial.jar, Pigs scripts, log files). These files work with Hadoop 0.18 and provide everything you need to run the Pig scripts. To get started, follow these basic steps:

  1. Install Java.
  2. Download the Pig tutorial file and install Pig.
  3. Run the Pig scripts - in local mode or on a Hadoop cluster.

Java Installation

Make sure your run-time environment includes the following:

  1. Java 1.6 or higher (preferably from Sun)
  2. The JAVA_HOME environment variable is set the root of your Java installation.

Pig Installation

To install Pig, do the following:

  1. Download the Pig tutorial file to your local directory (pigtutorial.tar.gz)
  2. Unzip the Pig tutorial file (the files are stored in a newly created directory, pigtmp).
    Code Block
    $ tar -xzf pigtutorial.tar.gz
    
  3. Move to the pigtmp directory.
  4. Review the contents of the Pig tutorial file.
  5. Copy the pig.jar file to the appropriate directory on your system. For example: /home/me/pig.
  6. Create an environment variable, PIGDIR, and point it to your directory. For example: export PIGDIR=/home/me/pig (bash, sh) or setenv PIGDIR /home/me/pig (tcsh, csh).

Pig Scripts: Local Mode

To run the Pig scripts in local mode, do the following:

  1. Move to the pigtmp directory.
  2. Review Pig Script 1 and Pig Script 2.
  3. Execute the following command (using either script1-local.pig or script2-local.pig).
    Code Block
    $ java -cp $PIGDIR/pig.jar org.apache.pig.Main -x local script1-local.pig
    
  4. Review the result file (either script1-local-results.txt or script2-local-results.txt):
    Code Block
    $ ls -l script1-local-results.txt
    $ cat script1-local-results.txt
    

Pig Scripts: Hadoop Mode

To run the Pig scripts in hadoop (mapreduce) mode, do the following:

  1. Move to the pigtmp directory.
  2. Review Pig Script 1 and Pig_Script_2.
  3. Copy the excite.log.bz2 file from the pigtmp directory to the HDFS directory.
    Code Block
    $ hadoop fs -copyFromLocal excite.log.bz2 .
    
  4. Set the HADOOPSITEPATH environment variable to the location of your hadoop-site.xml file.
  5. Execute the following command (using either script1-hadoop.pig or script2-hadoop.pig):
    Code Block
    $ java -cp $PIGDIR/pig.jar:$HADOOPSITEPATH org.apache.pig.Main script1-hadoop.pig
    
    1.#6 Review the result files (located in either the script1-hadoop-results or script2-hadoop-results HDFS directory):
Code Block
$ hadoop fs -ls script1-hadoop-results
$ hadoop fs -cat 'script1-hadoop-results/*' | less

Anchor
Pig_Tutorial_File
Pig_Tutorial_File

Pig Tutorial File

The contents of the Pig tutorial file (pigtutorial.tar.gz) are described here.

File

Description

pig.jar

Pig JAR file

tutorial.jar

User-defined functions (UDFs) and Java classes

script1-local.pig

Pig Script 1, Query Phrase Popularity (local mode)

script1-hadoop.pig

Pig Script 1, Query Phrase Popularity (Hadoop cluster)

script2-local.pig

Pig Script 2, Temporal Query Phrase Popularity (local mode)

script2-hadoop.pig

Pig Script 2, Temporal Query Phrase Popularity (Hadoop cluster)

excite-small.log

Log file, Excite search engine (local mode)

excite.log.bz2

Log file, Excite search engine (Hadoop cluster)

A better-documented version of script1-local.pig can be found at https://cwiki.apache.org/confluence/download/attachments/27822259/script1-local-with-added-documentation.pig . It includes comments showing samples from each intermediate relation.

The user-defined functions (UDFs) are described here.

UDF

Description

ExtractHour

Extracts the hour from the record.

NGramGenerator

Composes n-grams from the set of words.

NonURLDetector

Removes the record if the query field is empty or a URL.

ScoreGenerator

Calculates a "popularity" score for the n-gram.

ToLower

Changes the query field to lowercase.

TutorialUtil

Divides the query string into a set of words.

Anchor
Pig_Script_1
Pig_Script_1

Pig Script 1: Query Phrase Popularity

The Query Phrase Popularity script (script1-local.pig or script1-hadoop.pig) processes a search query log file from the Excite search engine and finds search phrases that occur with particular high frequency during certain times of the day.

The script is shown here:

  • Register the tutorial JAR file so that the included UDFs can be called in the script.
    Code Block
    REGISTER ./tutorial.jar; 
    
  • Use the PigStorage function to load the excite log file (excite.log or excite-small.log) into the "raw" bag as an array of records with the fields user, time, and query.
    Code Block
    raw = LOAD 'excite.log' USING PigStorage('\t') AS (user, time, query);
    
  • Call the NonURLDetector UDF to remove records if the query field is empty or a URL.
    Code Block
    clean1 = FILTER raw BY org.apache.pig.tutorial.NonURLDetector(query);
    
  • Call the ToLower UDF to change the query field to lowercase.
    Code Block
    clean2 = FOREACH clean1 GENERATE user, time, org.apache.pig.tutorial.ToLower(query) as query;
    
  • Because the log file only contains queries for a single day, we are only interested in the hour. The excite query log timestamp format is YYMMDDHHMMSS. Call the ExtractHour UDF to extract the hour (HH) from the time field.
    Code Block
    houred = FOREACH clean2 GENERATE user, org.apache.pig.tutorial.ExtractHour(time) as hour, query;
    
  • Call the NGramGenerator UDF to compose the n-grams of the query.
    Code Block
     
    ngramed1 = FOREACH houred GENERATE user, hour, flatten(org.apache.pig.tutorial.NGramGenerator(query)) as ngram;
    
  • Use the DISTINCT command to get the unique n-grams for all records.
    Code Block
     
    ngramed2 = DISTINCT ngramed1;
    
  • Use the GROUP command to group records by n-gram and hour.
    Code Block
     
    hour_frequency1 = GROUP ngramed2 BY (ngram, hour);
    
  • Use the COUNT function to get the count (occurrences) of each n-gram.
    Code Block
     
    hour_frequency2 = FOREACH hour_frequency1 GENERATE flatten($0), COUNT($1) as count;
    
  • Use the GROUP command to group records by n-gram only. Each group now corresponds to a distinct n-gram and has the count for each hour.
    Code Block
     
    uniq_frequency1 = GROUP hour_frequency2 BY group::ngram;
    
  • For each group, identify the hour in which this n-gram is used with a particularly high frequency. Call the ScoreGenerator UDF to calculate a "popularity" score for the n-gram.
    Code Block
     
    uniq_frequency2 = FOREACH uniq_frequency1 GENERATE flatten($0), flatten(org.apache.pig.tutorial.ScoreGenerator($1));
    
  • Use the FOREACH-GENERATE command to assign names to the fields.
    Code Block
     
    uniq_frequency3 = FOREACH uniq_frequency2 GENERATE $1 as hour, $0 as ngram, $2 as score, $3 as count, $4 as mean;
    
  • Use the FILTER command to move all records with a score less than or equal to 2.0.
    Code Block
     
    filtered_uniq_frequency = FILTER uniq_frequency3 BY score > 2.0;
    
  • Use the ORDER command to sort the remaining records by hour and score.
    Code Block
     
    ordered_uniq_frequency = ORDER filtered_uniq_frequency BY (hour, score);
    
  • Use the PigStorage function to store the results. The output file contains a list of n-grams with the following fields: hour, ngram, score, count, mean.
    Code Block
     
    STORE ordered_uniq_frequency INTO '/tmp/tutorial-results' USING PigStorage(); 
    

Anchor
Pig_Script_2
Pig_Script_2

Pig Script 2: Temporal Query Phrase Popularity

The Temporal Query Phrase Popularity script (script2-local.pig or script2-hadoop.pig) processes a search query log file from the Excite search engine and compares the occurrence of frequency of search phrases across two time periods separated by twelve hours.

The script is shown here:

  • Register the tutorial JAR file so that the user-defined functions (UDFs) can be called in the script.
    Code Block
    REGISTER ./tutorial.jar;
    
  • Use the PigStorage function to load the excite log file (excite.log or excite-small.log) into the "raw" bag as an array of records with the fields user, time, and query.
    Code Block
    raw = LOAD 'excite.log' USING PigStorage('\t') AS (user, time, query);
    
  • Call the NonURLDetector UDF to remove records if the query field is empty or a URL.
    Code Block
    clean1 = FILTER raw BY org.apache.pig.tutorial.NonURLDetector(query);
    
  • Call the ToLower UDF to change the query field to lowercase.
    Code Block
    clean2 = FOREACH clean1 GENERATE user, time, org.apache.pig.tutorial.ToLower(query) as query;
    
  • Because the log file only contains queries for a single day, we are only interested in the hour. The excite query log timestamp format is YYMMDDHHMMSS. Call the ExtractHour UDF to extract the hour from the time field.
    Code Block
    houred = FOREACH clean2 GENERATE user, org.apache.pig.tutorial.ExtractHour(time) as hour, query;
    
  • Call the NGramGenerator UDF to compose the n-grams of the query.
    Code Block
    ngramed1 = FOREACH houred GENERATE user, hour, flatten(org.apache.pig.tutorial.NGramGenerator(query)) as ngram;
    
  • Use the DISTINCT command to get the unique n-grams for all records.
    Code Block
    ngramed2 = DISTINCT ngramed1;
    
  • Use the GROUP command to group the records by n-gram and hour.
    Code Block
    hour_frequency1 = GROUP ngramed2 BY (ngram, hour);
    
  • Use the COUNT function to get the count (occurrences) of each n-gram.
    Code Block
    hour_frequency2 = FOREACH hour_frequency1 GENERATE flatten($0), COUNT($1) as count;
    
  • Use the FOREACH-GENERATE command to assign names to the fields.
    Code Block
    hour_frequency3 = FOREACH hour_frequency2 GENERATE $0 as ngram, $1 as hour, $2 as count;
    
  • Use the FILTER command to get the n-grams for hour '00'
    Code Block
    hour00 = FILTER hour_frequency2 BY hour eq '00';
    
  • Uses the FILTER command to get the n-grams for hour '12'
    Code Block
    hour12 = FILTER hour_frequency3 BY hour eq '12';
    
  • Use the JOIN command to get the n-grams that appear in both hours.
    Code Block
    same = JOIN hour00 BY $0, hour12 BY $0;
    
  • Use the FOREACH-GENERATE command to record their frequency.
    Code Block
    same1 = FOREACH same GENERATE hour_frequency2::hour00::group::ngram as ngram, $2 as count00, $5 as count12;
    
  • Use the PigStorage function to store the results. The output file contains a list of n-grams with the following fields: hour, count00, count12.
    Code Block
    STORE same1 INTO '/tmp/tutorial-join-results' USING PigStorage();