Apache Pig - 诊断操作符

load 语句会将数据简单地加载到 Apache Pig 中指定的关联中。要验证Load语句的执行，必须使用诊断操作符。Pig Latin 提供四种不同类型的诊断操作符：

Dump 操作符
Describe 操作符
Explain 操作符
Illustrate 操作符

本章将讨论 Pig Latin 的 Dump 操作符。

Dump 操作符

Dump 操作符用于运行 Pig Latin 语句并在屏幕上显示结果。它通常用于调试目的。

语法

以下是Dump操作符的语法。

grunt> Dump Relation_Name

示例

假设我们在 HDFS 中有一个文件student_data.txt，内容如下。

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.

我们使用 LOAD 操作符将其读取到名为student的关联中，如下所示。

grunt> student = LOAD 'hdfs://127.0.0.1:9000/pig_data/student_data.txt' 
   USING PigStorage(',')
   as ( id:int, firstname:chararray, lastname:chararray, phone:chararray, 
   city:chararray );

现在，让我们使用Dump 操作符打印关联的内容，如下所示。

grunt> Dump student

执行上述Pig Latin语句后，它将启动一个 MapReduce 作业来从 HDFS 读取数据。它将产生以下输出。

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://127.0.0.1:9000/tmp/temp580182027/tmp757878456,

Input(s): Successfully read 0 records from: "hdfs://127.0.0.1:9000/pig_data/
student_data.txt"
  
Output(s): Successfully stored 0 records in: "hdfs://127.0.0.1:9000/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,siddarth,Battacharya,9848022338,Kolkata)
(3,Rajesh,Khanna,9848022339,Delhi)
(4,Preethi,Agarwal,9848022330,Pune)
(5,Trupthi,Mohanthy,9848022336,Bhuwaneshwar)
(6,Archana,Mishra,9848022335,Chennai)

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