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From "Runping Qi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2774) Add counters to show number of key/values that have been sorted and merged in the maps and reduces
Date Sun, 26 Oct 2008 17:50:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642808#action_12642808
] 

Runping Qi commented on HADOOP-2774:
------------------------------------


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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