The load statement will simply load the data into the specified relation in Apache Pig. To verify the execution of the Load statement, you have to use the Diagnostic Operators. Pig Latin provides four different types of diagnostic operators −

• Dump operator
• Describe operator
• Explanation operator

• Illustration operator

Dump Operator

The Dump operator is used to run the Pig Latin statements and display the results on the screen. It is generally used for debugging Purpose.

Syntax

Given below is the syntax of the Dump operator.

grunt> Dump Relation_Name

Example

Assume we have a file student_data.txt in HDFS with the following content.

001,Rajiv,Reddy,9848022337,Hyderabad
002,siddarth,Battacharya,9848022338,Kolkata
003,Rajesh,Khanna,9848022339,Delhi
004,Preethi,Agarwal,9848022330,Pune
005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar
006,Archana,Mishra,9848022335,Chennai.

And we have read it into a relation student using the LOAD operator as shown below.

grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt' 
   USING PigStorage(',')
   as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, 
   city:chararray );

Now, let us print the contents of the relation using the Dump operator as shown below.

grunt
> Dump student

Once you execute the above Pig Latin statement, it will start a MapReduce job to read data from HDFS.

DESCRIBE Operator:

Thedescribeoperator is used to view the schema of a relation.

Syntax

The syntax of the describe operator is as follows −

grunt> Describe Relation_name

Now, let us describe the relation namedstudentand verify the schema as shown below.

grunt> describe student;

Output

Once you execute the above Pig Latin statement, it will produce the following output.

grunt
> student: { id: int,firstname: chararray,lastname: chararray,phone: chararray,city: chararray }

EXPLAIN Operator:

The explain operator is used to display the logical, physical, and MapReduce execution plans of a relation.

Syntax

Given below is the syntax of theexplainoperator.

grunt> explain Relation_name;

Example

Assume we have a file student_data.txt in HDFS with the following content.

001,Rajiv,Reddy,9848022337,Hyderabad
002,siddarth,Battacharya,9848022338,Kolkata
003,Rajesh,Khanna,9848022339,Delhi
004,Preethi,Agarwal,9848022330,Pune
005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar
006,Archana,Mishra,9848022335,Chennai.

And we have read it into a relation student using the LOAD operator as shown below.

grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt' 
   USING PigStorage(',')
   as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, 
   city:chararray );

Now, let us explain the relation named student using the explain operator as shown below.

grunt> explain student;

ILLUSTRATE Operator:

The illustrate operator gives you the step-by-step execution of a sequence of statements.

Syntax

Given below is the syntax of the illustrate operator.

grunt> illustrate Relation_name;

Example

Assume we have a file student_data.txt in HDFS with the following content.

001,Rajiv,Reddy,9848022337,Hyderabad
002,siddarth,Battacharya,9848022338,Kolkata 
003,Rajesh,Khanna,9848022339,Delhi
004,Preethi,Agarwal,9848022330,Pune 
005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar
006,Archana,Mishra,9848022335,Chennai.

And we have read it into a relation student using the LOAD operator as shown below.

grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt' 
   USING PigStorage(',')
   as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, 
   city:chararray );

Now, let us illustrate the relation named student as shown below.

grunt> illustrate student;

Output

On executing the above statement, you will get the following output.

grunt> illustrate student;

INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigMapOnly$M ap - Aliases
being processed per job phase (AliasName[line,offset]): M: student[1,10] C:  R:
---------------------------------------------------------------------------------------------
|student | id:int | firstname:chararray | lastname:chararray | phone:chararray | city:chararray |
--------------------------------------------------------------------------------------------- 
|        | 002    | siddarth            | Battacharya        | 9848022338      | Kolkata        |
---------------------------------------------------------------------------------------------