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From "Chris Douglas (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 Thu, 20 Nov 2008 23:26:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12649530#action_12649530
] 

Chris Douglas commented on HADOOP-2774:
---------------------------------------

Does the merger require two different counters? Isn't it sufficient to pass an optional counter
for each record the merger emits? The caller should have enough context to know whether the
segments are coming to/from disk or memory... right?

Overall, the plan sounds good. This section of code is particular enough that it might be
easier to reason about a patch, even a partial one. There are some edge cases that may limit
the implementation.

> 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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