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https://issues.apache.org/jira/browse/HADOOP-153?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12593930#action_12593930
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Yiping Han commented on HADOOP-153:
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I suggest a transactional emit() interface to be supplement to this proposal.
When an exception happens, there might already be some partial output be
emitted from the mapper. In some use cases, such partial output should be
considered garbage and harmful. So I suggest a transactional emit mode, such
that the Collector should buffer the output records from mapper and until the
mappers calls a commit() operation, they are actually submitted. At the
beginning of the map() function, the mapper should call a start() operation
which discards any records remaining in the Collector.
> 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: Devaraj Das
>
> 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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