[jira] Resolved: (MAPREDUCE-2212) MapTask and ReduceTask should only compress/decompress the final map output file

["Scott Chen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-2212?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Scott Chen resolved MAPREDUCE-2212.
-----------------------------------

    Resolution: Won't Fix

I am closing this now because I think there is no much benefit to do this.
This will increase complexity of the code.

> MapTask and ReduceTask should only compress/decompress the final map output file
> --------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-2212
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2212
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: task
>    Affects Versions: 0.23.0
>            Reporter: Scott Chen
>            Assignee: Scott Chen
>             Fix For: 0.23.0
>
>
> Currently if we set mapred.map.output.compression.codec
> 1. MapTask will compress every spill, decompress every spill, merge and compress the final map output file
> 2. ReduceTask will decompress, merge and compress every map output file. And repeat the compression/decompression every pass.
> This causes all the data being compressed/decompressed many times.
> The reason we need mapred.map.output.compression.codec is for network traffic.
> We should not compress/decompress the data again and again during merge sort.
> We should only compress the final map output file that will be transmitted over the network.

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