[jira] Commented: (HADOOP-5266) Values Iterator should support "mark" and "reset"

["Jothi Padmanabhan (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-5266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12673913#action_12673913 ] 

Jothi Padmanabhan commented on HADOOP-5266:
-------------------------------------------

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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