Pig Dump 运算符 | Pig 教程

#Pig Dump 运算符
Dump 运算符，也就是诊断运算符。
 
load 语句将简单地将数据加载到Apache pig 指定的关系。要验证Load语句的执行，您必须使用Diagnostic（诊断）操作符。Pig Latin提供四种不同类型的诊断运算符：
- Dump 运算符
- Describe 运算符
- Explanation 运算符
- Illustration 运算符

在本章中，我们将讨论Pig Latin的Dump运算符。

##Dump 运算符
Dump 操作来运行的Pig Latin语句并在屏幕上显示的结果。它通常用于调试目的。
###语法
下面给出的是Dump运算符的语法。
```bash
grunt> Dump Relation_Name
```
假设我们在HDFS中有一个具有以下内容的文件Student_data.txt。
```bash
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.
```
如下所示，我们已使用LOAD运算符将其读入关系学生。
```bash
grunt> student = LOAD 'hdfs://localhost: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运算符打印关系的内容，如下所示。
```bash
grunt> Dump student
```
一旦执行了上述Pig Latin语句，它将启动MapReduce作业以从HDFS读取数据。它将产生以下输出。

```bash
2020-10-01 15:05:27,642 [main]
INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher - 
100% complete
2020-10-01 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  2020-10-01 15:03:11  2020-10-01 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
  
2020-10-01 15:06:28,403 [main]
INFO  org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLau ncher - Success!
2020-10-01 15:06:28,441 [main] INFO  org.apache.pig.data.SchemaTupleBackend - 
Key [pig.schematuple] was not set... will not generate code.
2020-10-01 15:06:28,485 [main]
INFO  org.apache.hadoop.mapreduce.lib.input.FileInputFormat - Total input paths 
to process : 1
2020-10-01 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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