apache-pig - 如何在 Apache Pig 上执行正确的数据类型？

Question

由于数据类型错误，我无法对一包值求和。

当我加载一个 csv 文件时，其行如下所示:

6   574 false   10.1.72.23  2010-05-16 13:56:19 +0930   fbcdn.net   static.ak.fbcdn.net 304 text/css    1   /rsrc.php/zPTJC/hash/50l7x7eg.css   http    pwong

使用以下内容:

logs_base = FOREACH raw_logs GENERATE
  FLATTEN(
     EXTRACT(line, '^(\\d+),"(\\d+)","(\\w+)","(\\S+)","(.+?)","(\\S+)","(\\S+)","(\\d+)","(\\S+)","(\\d+)","(\\S+)","(\\S+)","(\\S+)"')
  )
  as (
    account_id: int,
    bytes: long,
    cached: chararray,
    ip: chararray,
    time: chararray,
    domain: chararray,
    host: chararray,
    status: chararray,
    mime_type: chararray,
    page_view: chararray,
    path: chararray,
    protocol: chararray,
    username: chararray
  );

所有字段似乎都加载正常，并且类型正确，如“describe”命令所示:

grunt> describe logs_base
logs_base: {account_id: int,bytes: long,cached: chararray,ip: chararray,time: chararray,domain: chararray,host: chararray,status: chararray,mime_type: chararray,page_view: chararray,path: chararray,protocol: chararray,username: chararray}

每当我使用以下方法执行 SUM 时:

bytesCount = FOREACH (GROUP logs_base ALL) GENERATE SUM(logs_base.bytes);

并存储或转储内容，mapreduce 过程失败并出现以下错误:

org.apache.pig.backend.executionengine.ExecException: ERROR 2106: Error while computing sum in Initial
    at org.apache.pig.builtin.LongSum$Initial.exec(LongSum.java:87)
    at org.apache.pig.builtin.LongSum$Initial.exec(LongSum.java:65)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:216)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:253)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.getNext(PhysicalOperator.java:334)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.processPlan(POForEach.java:332)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POForEach.getNext(POForEach.java:284)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.PhysicalOperator.processInput(PhysicalOperator.java:290)
    at org.apache.pig.backend.hadoop.executionengine.physicalLayer.relationalOperators.POLocalRearrange.getNext(POLocalRearrange.java:256)
    at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.runPipeline(PigGenericMapBase.java:267)
    at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:262)
    at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigGenericMapBase.map(PigGenericMapBase.java:64)
    at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:771)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:375)
    at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:212)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long
    at org.apache.pig.builtin.LongSum$Initial.exec(LongSum.java:79)
    ... 15 more

引起我注意的一行是:

Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Long

这让我相信提取函数不会将字节字段转换为所需的数据类型(长)。

有没有办法强制提取功能转换为正确的数据类型？如何在不必对所有记录执行 FOREACH 的情况下转换该值？ (将时间转换为 unix 时间戳并尝试查找 MIN 时会发生同样的问题。我绝对想找到一个不需要不必要投影的解决方案)。

任何指针将不胜感激。非常感谢你的帮助。

问候，
豪尔赫 C.

附注我在 Amazon elastic mapreduce 服务上以交互模式运行它。

Answer 1

您是否尝试过 cast从 UDF 中检索到的数据？在此处应用架构不会执行任何转换。

例如

logs_base = 
   FOREACH raw_logs
   GENERATE
       FLATTEN(
           (tuple(LONG,LONG,CHARARRAY,....)) EXTRACT(line, '^...')
       )
       AS (account_id: INT, ...);