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https://issues.apache.org/jira/browse/TEZ-1608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14146322#comment-14146322
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Krisztian Horvath commented on TEZ-1608:
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In the second version every Sum processor maintains a local top K and only
writes these values when the task finishes, so the writer only has to select
the top K from the local top Ks. The implementation is a bit more complex than
the previous one.
> TopK example
> ------------
>
> Key: TEZ-1608
> URL: https://issues.apache.org/jira/browse/TEZ-1608
> Project: Apache Tez
> Issue Type: Sub-task
> Affects Versions: 0.5.0
> Reporter: Janos Matyas
> Attachments: TEZ-1608-1.patch, TEZ-1608-2.patch
>
>
> The goal of this sample is to find the topK elements of a dataset, while
> guiding through the basics of Tez (DAG creation, tokenizers, custom
> comparators and parallelism).
> An example use case for top K:
> Given a large data set in CSV format of user comments on a site listed as:
> userid,postid,commentid,comment,timestamp and we are looking for the top K
> commenter or the posts with the most comment.
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