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https://issues.apache.org/jira/browse/HADOOP-5266?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675067#action_12675067
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Doug Cutting commented on HADOOP-5266:
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> Would the 'mark/reset' functionality be still relevant for
> CombineValuesIterator so that we can add this in ValuesIterator or should
> this be just restricted to ReduceValuesIterator?
My instinct is to add a new interface like MarkableIterator or somesuch, that
only ReduceValuesIterator implements for now. If we later find a reason to use
it in CombineValuesIterator then we can implement it there then. I use
"interface" loosely. Since this appears in end-user APIs, it would better
permit compatible evolution if we use an abstract class. It's not absolutely
critical in this case, since we don't expect many users to implement this
interface, but, e.g., a FilterReducer might reasonably implement it, and an
abstract class would thus permit us to change this in ways that an interface
would not without breaking user code.
> 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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