PigTutorial

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:

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

Java Installation

Make sure your run-time environment includes the following:

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

Pig Installation

To install Pig, do the following:

Download the Pig tutorial file to your local directory (pigtutorial.tar.gz)
Unzip the Pig tutorial file (the files are stored in a newly created directory, pigtmp).
```
$ tar -xzf pigtutorial.tar.gz
```
Move to the pigtmp directory.
Review the contents of the Pig tutorial file.
Copy the pig.jar file to the appropriate directory on your system. For example: /home/me/pig.
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:

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

Move to the pigtmp directory.
Review Pig Script 1 and Pig_Script_2.
Copy the excite.log.bz2 file from the pigtmp directory to the HDFS directory.
```
$ hadoop fs -copyFromLocal excite.log.bz2 .
```
Set the HADOOPSITEPATH environment variable to the location of your hadoop-site.xml file.
Execute the following command (using either script1-hadoop.pig or script2-hadoop.pig):
```
$ 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):

$ hadoop fs -ls script1-hadoop-results
$ hadoop fs -cat 'script1-hadoop-results/*' | less

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.

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.
```
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.
```
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.
```
clean1 = FILTER raw BY org.apache.pig.tutorial.NonURLDetector(query);
```

Call the ToLower UDF to change the query field to lowercase.

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.
```
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.

 
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.
```
 
ngramed2 = DISTINCT ngramed1;
```

Use the GROUP command to group records by n-gram and hour.
```
 
hour_frequency1 = GROUP ngramed2 BY (ngram, hour);
```

Use the COUNT function to get the count (occurrences) of each n-gram.

 
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.
```
 
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.
```
 
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.

 
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.
```
 
filtered_uniq_frequency = FILTER uniq_frequency3 BY score > 2.0;
```

Use the ORDER command to sort the remaining records by hour and score.

 
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.
```
 
STORE ordered_uniq_frequency INTO '/tmp/tutorial-results' USING PigStorage(); 
```

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.