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What is Diagnostic Operators?

  • 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.

      • DUMP instruction:
        • Prints the content of a relation at standard output
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        grunt> Dump Relation_Name
        

        Example:

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

          001, Aadhira,Arushi  ,9848022337, Delhi
          002, Mahi,Champa,9848022338, Chennai
          003, Avantika,charu,9848022339, Pune
          004, Samaira,Hansa,9848022330, Kolkata
          005, Abhinav,Akaash,9848022336,Bhuwaneshwar
          006, Amarjeet,Aksat,9848022335, Hyderabad
          

          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, 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. It will produce the following output.

          2015-10-01 15:05:27,642 [main]
          INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher - 
          100% complete
          2015-10-01 15:05:27,652 [main]
          INFO  org.apache.pig.tools.pigstats.mapreduce.SimplePigStats - Script Statistics:   
          HadoopVersion  PigVersion  UserId    StartedAt             FinishedAt       Features             
          2.6.0          0.15.0      Hadoop  2015-10-01 15:03:11  2015-10-01 05:27     UNKNOWN
                                                          
          Success!  
          Job Stats (time in seconds):
            
          JobId           job_14459_0004
          Maps                 1  
          Reduces              0  
          MaxMapTime          n/a    
          MinMapTime          n/a
          AvgMapTime          n/a 
          MedianMapTime       n/a
          MaxReduceTime        0
          MinReduceTime        0  
          AvgReduceTime        0
          MedianReducetime     0
          Alias             student 
          Feature           MAP_ONLY        
          Outputs           hdfs://localhost:9000/tmp/temp580182027/tmp757878456,
          
          Input(s): Successfully read 0 records from: "hdfs://localhost:9000/pig_data/
          student_data.txt"
            
          Output(s): Successfully stored 0 records in: "hdfs://localhost:9000/tmp/temp580182027/
          tmp757878456"  
          
          Counters: Total records written : 0 Total bytes written : 0 Spillable Memory Manager 
          spill count : 0Total bags proactively spilled: 0 Total records proactively spilled: 0  
          
          Job DAG: job_1443519499159_0004
            
          2015-10-01 15:06:28,403 [main]
          INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLau ncher - Success!
          2015-10-01 15:06:28,441 [main] INFO  org.apache.pig.data.SchemaTupleBackend - 
          Key [pig.schematuple] was not set... will not generate code.
          2015-10-01 15:06:28,485 [main]
          INFO  org.apache.hadoop.mapreduce.lib.input.FileInputFormat - Total input paths 
          to process : 1
          2015-10-01 15:06:28,485 [main]
          INFO  org.apache.pig.backend.hadoop.executionengine.util.MapRedUtil - Total input paths
          to process : 1
          
          (1,Rajiv,Reddy,9848022337,Hyderabad)
           (2,Aadhira,Arushi  ,9848022337, Delhi)
          (3, Mahi,Champa,9848022338, Chennai)
          ( 4,Avantika,charu,9848022339, Pune)
          (5,Samaira,Hansa,9848022330, Kolkata)
           (6,Abhinav,Akaash,9848022336,Bhuwaneshwar)
          (7,Amarjeet,Aksat,9848022335, Hyderabad)
          

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