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From "John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-5649) Reduce cannot use more than 2G memory for the final merge
Date Thu, 19 Jun 2014 03:44:24 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5649?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14036910#comment-14036910
] 

John commented on MAPREDUCE-5649:
---------------------------------

$ find . -name "*.java" | xargs grep -Eni "Runtime.*getRuntime.*maxMemory"
$ find . -name "*.java" | grep "mapreduce" | xargs grep -Eni -A16 -B16 "Integer.MAX_VALUE"
> result

> Reduce cannot use more than 2G memory  for the final merge
> ----------------------------------------------------------
>
>                 Key: MAPREDUCE-5649
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5649
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: trunk
>            Reporter: stanley shi
>
> In the org.apache.hadoop.mapreduce.task.reduce.MergeManagerImpl.java file, in the finalMerge
method: 
>  int maxInMemReduce = (int)Math.min(
>         Runtime.getRuntime().maxMemory() * maxRedPer, Integer.MAX_VALUE);
>  
> This means no matter how much memory user has, reducer will not retain more than 2G data
in memory before the reduce phase starts.



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