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創(chuàng)新互聯(lián)ApachePig教程：ApachePigDiagnostic運算符
Load 語句會簡單地將數(shù)據(jù)加載到Apache Pig中的指定關系中。要驗證Load語句的執(zhí)行，必須使用Diagnostic運算符。Pig Latin提供四種不同類型的診斷運算符:
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- Dump運算符
- Describe運算符
- Explanation運算符
- Illustration運算符
在本章中，我們將討論Pig Latin的Dump運算符。
Dump運算符
Dump 運算符用于運行Pig Latin語句，并在屏幕上顯示結(jié)果，它通常用于調(diào)試目的。
語法
下面給出了 Dump 運算符的語法。
grunt> Dump Relation_Name
例
假設在HDFS中有一個包含以下內(nèi)容的文件 student_data.txt 。
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運算符將它讀入關系 student ，如下所示。
grunt> student = LOAD 'hdfs://localhost:9000/pig_data/student_data.txt'
USING PigStorage(',')
as ( id:int, firstname:chararray, lastname:chararray, phone:chararray,
city:chararray );
現(xiàn)在，使用Dump運算符打印關系的內(nèi)容，如下所示。
grunt> Dump student
一旦執(zhí)行上述 Pig Latin 語句，將啟動一個MapReduce作業(yè)以從HDFS讀取數(shù)據(jù)，將產(chǎn)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://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,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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文章鏈接：http://fisionsoft.com.cn/article/cciigei.html
