load 语句只是将数据加载到Apache Pig中的指定关系中.要验证 Load 语句的执行，您必须使用诊断运算符. Pig Latin提供四种不同类型的诊断算子 :
转储运算符
描述运算符
解释运算符
插图运算符
在本章中，我们将讨论Pig Latin的转储运算符.
转储运算符
转储运算符用于运行Pig Latin语句并在屏幕上显示结果.它通常用于调试目的.
语法
以下是转储运算符的语法.
grunt> Dump Relation_Name
示例
假设我们在HDFS中有一个文件 student_data.txt 以下内容.
001,Rajiv,Reddy,9848022337,Hyderabad002,siddarth,Battacharya,9848022338,Kolkata003,Rajesh,Khanna,9848022339,Delhi004,Preethi,Agarwal,9848022330,Pune005,Trupthi,Mohanthy,9848022336,Bhuwaneshwar006,Archana,Mishra,9848022335,Chennai.
我们已经使用LOAD运算符将其读入关系 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，让我们使用转储运算符打印关系的内容，如下所示.
grunt> Dump student
执行上述 Pig Latin 语句后，它将启动MapReduce作业以从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% complete2015-10-01 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_0004Maps 1 Reduces 0 MaxMapTime n/a MinMapTime n/aAvgMapTime n/a MedianMapTime n/aMaxReduceTime 0MinReduceTime 0 AvgReduceTime 0MedianReducetime 0Alias 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 : 12015-10-01 15:06:28,485 [main]INFO org.apache.pig.backend.hadoop.executionengine.util.MapRedUtil - Total input pathsto 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)