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https://issues.apache.org/jira/browse/HADOOP-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642808#action_12642808
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Runping Qi commented on HADOOP-2774:
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Owen, I think the number of spills is more important than you think.
Consider these two cases:
1. a task writes 1000 spills, each 10000 records, totalling 10M records.
2. a task writes 100 spills, each with 100000 records, totaling 10M records.
With mergeing factor being 100, the case 2 does not second level merge, while
the case 2 does.
The case 1 requires 2x read/writes of the case 1.
> 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
>
> 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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