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From "Jerry Chen (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-4882) Error in estimating the length of the output file in Spill Phase
Date Sat, 26 Jan 2013 11:41:13 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-4882?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Jerry Chen updated MAPREDUCE-4882:
----------------------------------

    Target Version/s: trunk  (was: 0.20.2, 1.0.3)
              Status: Patch Available  (was: Open)

Patch for fixing the problem attached.

Change from "(bufvoid - bufend) + bufstart" to "(bufvoid - bufstart) + bufend" and add test
case for detecting invalid estimation size as for the case of bufend < bufstart, (bufvoid
- bufend) + bufstart will greater than bufvoid.

Please kindly help review the patch.
                
> 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: 1.0.3, 0.20.2
>         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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