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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4882) Error in estimating the length of the output file in Spill Phase
Date Sat, 02 May 2015 04:25:08 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14524601#comment-14524601
] 

Hadoop QA commented on MAPREDUCE-4882:
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| (x) *{color:red}-1 overall{color}* |
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|| Vote || Subsystem || Runtime || Comment ||
| {color:red}-1{color} | patch |   0m  0s | The patch command could not apply the patch during
dryrun. |
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|| Subsystem || Report/Notes ||
| Patch URL | http://issues.apache.org/jira/secure/attachment/12566626/MAPREDUCE-4882.patch
|
| Optional Tests | javadoc javac unit findbugs checkstyle |
| git revision | trunk / f1a152c |
| Console output | https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/5507/console |


This message was automatically generated.

> Error in estimating the length of the output file in Spill Phase
> ----------------------------------------------------------------
>
>                 Key: MAPREDUCE-4882
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4882
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 0.20.2, 1.0.3
>         Environment: Any Environment
>            Reporter: Lijie Xu
>            Assignee: Jerry Chen
>              Labels: patch
>         Attachments: MAPREDUCE-4882.patch
>
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> The sortAndSpill() method in MapTask.java has an error in estimating the length of the
output file. 
> The "long size" should be "(bufvoid - bufstart) + bufend" not "(bufvoid - bufend) + bufstart"
when "bufend < bufstart".
> Here is the original code in MapTask.java.
>  private void sortAndSpill() throws IOException, ClassNotFoundException,
>                                        InterruptedException {
>       //approximate the length of the output file to be the length of the
>       //buffer + header lengths for the partitions
>       long size = (bufend >= bufstart
>           ? bufend - bufstart
>           : (bufvoid - bufend) + bufstart) +
>                   partitions * APPROX_HEADER_LENGTH;
>       FSDataOutputStream out = null;
> ------------------------------------------------------------------------------
> I had a test on "TeraSort". A snippet from mapper's log is as follows:
> MapTask: Spilling map output: record full = true
> MapTask: bufstart = 157286200; bufend = 10485460; bufvoid = 199229440
> MapTask: kvstart = 262142; kvend = 131069; length = 655360
> MapTask: Finished spill 3
> In this occasioin, Spill Bytes should be (199229440 - 157286200) + 10485460 = 52428700
(52 MB) because the number of spilled records is 524287 and each record costs 100B.



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