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https://issues.apache.org/jira/browse/HADOOP-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649621#action_12649621
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Ravi Gummadi commented on HADOOP-2774:
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As ShuffleToDisk( ) is causing the problem of counting records when directly
written to disk without processing, we decided to count the records when they
are read from disk in reduce phase(which is same as the number of records
written to disk in reuce phase). As Merger.merge is called from both Map and
Reduce, merge should be able to count records written to disk(useful when merge
is called from Map phase) and records read from disk(useful wnhen merge is
called from Reduce phase) separately --- thus 2 counters.
> Add counters to show number of key/values that have been sorted and merged in
> the maps and reduces
> --------------------------------------------------------------------------------------------------
>
> Key: HADOOP-2774
> URL: https://issues.apache.org/jira/browse/HADOOP-2774
> Project: Hadoop Core
> Issue Type: Bug
> Reporter: Owen O'Malley
> Assignee: Ravi Gummadi
> Fix For: 0.20.0
>
> Attachments: HADOOP-2774.patch, HADOOP-2774.patch
>
>
> For each *pass* of the sort and merge, I would like a count of the number of
> records. So for example, if the map output 100 records and they were sorted
> once, the counter would be 100. If it spilled twice and was merged together,
> it would be 200. Clearly in a multi-level merge, it may not be a multiple of
> the number of map output records. This would let the users easily see if they
> have values like io.sort.mb or io.sort.factor set too low.
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