Apache Pig Diagnostic运算符
Load 语句会简单地将数据加载到Apache Pig中的指定关系中。要验证Load语句的执行，必须使用Diagnostic运算符。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 运算符用于运行Pig Latin语句，并在屏幕上显示结果，它通常用于调试目的。
语法
下面给出了 Dump 运算符的语法。
grunt> Dump Relation_Name
例
假设在HDFS中有一个包含以下内容的文件 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.
我们使用LOAD运算符将它读入关系 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 );
现在，使用Dump运算符打印关系的内容，如下所示。
grunt> Dump student
一旦执行上述 Pig Latin 语句，将启动一个MapReduce作业以从HDFS读取数据，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://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)
