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From "Yiqun Lin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-6795) Update the document for JobConf#setNumReduceTasks
Date Sun, 30 Oct 2016 06:05:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6795?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15619360#comment-15619360
] 

Yiqun Lin commented on MAPREDUCE-6795:
--------------------------------------

Thanks [~ajisakaa] for reporting this. I'd like to make a quick fix. But it seems that I am
not a contributor of MAPREDUCE now and I can't upload my patch. The patch file created in
my local:

{code}
diff --git a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobConf.java
b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobConf.java
index f2b0aae..c8b0458 100644
--- a/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobConf.java
+++ b/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/JobConf.java
@@ -1347,9 +1347,9 @@ public void setReduceSpeculativeExecution(boolean speculativeExecution)
{
    * <b id="NoOfReduces">How many reduces?</b>
    * 
    * <p>The right number of reduces seems to be <code>0.95</code> or 
-   * <code>1.75</code> multiplied by (&lt;<i>no. of nodes</i>&gt;
* 
-   * <a href="{@docRoot}/../mapred-default.html#mapreduce.tasktracker.reduce.tasks.maximum">
-   * mapreduce.tasktracker.reduce.tasks.maximum</a>).
+   * <code>1.75</code> multiplied by (
+   * <a href="{@docRoot}/../mapred-default.html#mapreduce.job.running.reduce.limit">
+   * mapreduce.job.running.reduce.limit</a>).
    * </p>
    * 
    * <p>With <code>0.95</code> all of the reduces can launch immediately
and 
{code}

I think the value {{numNodes * mapreduce.tasktracker.reduce.tasks.maximum}} in MRV1 is equal
to the current config {{mapreduce.job.running.reduce.limit}}. Correct me if I am wrong. Thanks!

> Update the document for JobConf#setNumReduceTasks
> -------------------------------------------------
>
>                 Key: MAPREDUCE-6795
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6795
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: documentation
>            Reporter: Akira Ajisaka
>
> The following document is for MRv1. We should update the document for MapReduce on YARN.
> {code:title=JobConf.java}
>    * <b id="NoOfReduces">How many reduces?</b>
>    * 
>    * <p>The right number of reduces seems to be <code>0.95</code> or

>    * <code>1.75</code> multiplied by (&lt;<i>no. of nodes</i>&gt;
* 
>    * <a href="{@docRoot}/../mapred-default.html#mapreduce.tasktracker.reduce.tasks.maximum">
>    * mapreduce.tasktracker.reduce.tasks.maximum</a>).
>    * </p>
> {code}



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