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From "Enis Soztutar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-153) skip records that throw exceptions
Date Wed, 25 Jun 2008 07:32:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12607877#action_12607877
] 

Enis Soztutar commented on HADOOP-153:
--------------------------------------

bq. Instead of keeping bad records ids in JobTracker's TIP object, I would prefer keeping
it in FileSystem along with other job files. This would allows us to be more scalable as no
of bad records could potentially be high.
I think the number of bad records *supposed to be* low. If the job fails in lots of records,
then there should be some problem with the implementation itself. 
I guess the number of bad records per job should be on the order of hundreds max. While working
with nutch, there were just several records which caused StackOverflow by the third-party
html parsers ,out of millions of urls.  
Can you give us an example percentage of bad records that you see in the jobs at Y!  

> skip records that throw exceptions
> ----------------------------------
>
>                 Key: HADOOP-153
>                 URL: https://issues.apache.org/jira/browse/HADOOP-153
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>    Affects Versions: 0.2.0
>            Reporter: Doug Cutting
>            Assignee: Sharad Agarwal
>         Attachments: skipRecords_wip1.patch
>
>
> MapReduce should skip records that throw exceptions.
> If the exception is thrown under RecordReader.next() then RecordReader implementations
should automatically skip to the start of a subsequent record.
> Exceptions in map and reduce implementations can simply be logged, unless they happen
under RecordWriter.write().  Cancelling partial output could be hard.  So such output errors
will still result in task failure.
> This behaviour should be optional, but enabled by default.  A count of errors per task
and job should be maintained and displayed in the web ui.  Perhaps if some percentage of records
(>50%?) result in exceptions then the task should fail.  This would stop jobs early that
are misconfigured or have buggy code.
> Thoughts?

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