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https://issues.apache.org/jira/browse/HADOOP-5266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12673913#action_12673913
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Jothi Padmanabhan commented on HADOOP-5266:
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Users would call values.mark() and values.reset() to use this functionality.
However, the current Reduce API takes Iterator values as the parameter.
{code}
public void reduce(K key, Iterator<V> values,
OutputCollector<K, V> output,
Reporter reporter)
{code}
Since the generic Iterator does not include functions mark and reset, how
should this be handled? For example
# Change the API to take a ResettableIterator that extends Iterator and
supports these two extra methods. However, this will break existing
applications and so not an option
# Let the API take Iterator, but let the framework return a Resetabble Iterator
and user code does a cast to ResettableIterator
# Some other way?
Thoughts?
> Values Iterator should support "mark" and "reset"
> -------------------------------------------------
>
> Key: HADOOP-5266
> URL: https://issues.apache.org/jira/browse/HADOOP-5266
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Jothi Padmanabhan
> Assignee: Jothi Padmanabhan
> Fix For: 0.21.0
>
>
> Some users have expressed interest in having a mark-reset functionality on
> values iterator. Users can call mark() at any point during the iteration
> process and a subsequent reset() should move the iterator to the last value
> emitted when mark() was called.
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