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From "Sharad Agarwal (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-153) skip records that throw exceptions
Date Wed, 25 Jun 2008 09:08:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12607902#action_12607902
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Sharad Agarwal commented on HADOOP-153:
---------------------------------------

I assume there would be use cases in which a higher bad records percentage could be acceptable
say jobs related to log mining, crawling, indexing, analysis for research purposes etc.
That said, even 1 % of acceptable bad records could turn out to be a big no given that hadoop
jobs are generally suitable for huge data. Piggybacking on jobtracker's memory for this may
not be a good idea. Transferring the whole list over rpc would not be ideal.
Also, the need to persist may arise due to HADOOP-3245.

> 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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