Apache Pig - 診斷運算子

load 語句會將資料簡單地載入到 Apache Pig 中指定的關聯中。要驗證Load語句的執行，必須使用診斷運算子。Pig Latin 提供四種不同型別的診斷運算子：

• Dump 運算子
• Describe 運算子
• Explain 運算子
• Illustrate 運算子

本章將討論 Pig Latin 的 Dump 運算子。

Dump 運算子

Dump 運算子用於執行 Pig Latin 語句並在螢幕上顯示結果。它通常用於除錯目的。

語法

以下是Dump運算子的語法。

grunt> Dump Relation_Name

示例

假設我們在 HDFS 中有一個檔案student_data.txt，內容如下。

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.

我們使用 LOAD 運算子將其讀取到名為student的關聯中，如下所示。

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

現在，讓我們使用Dump 運算子列印關聯的內容，如下所示。

grunt> Dump student

執行上述Pig Latin語句後，它將啟動一個 MapReduce 作業來從 HDFS 讀取資料。它將產生以下輸出。

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

Input(s): Successfully read 0 records from: "hdfs://:9000/pig_data/
student_data.txt"
  
Output(s): Successfully stored 0 records in: "hdfs://: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)