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From "Scott Chen (JIRA)" <j...@apache.org>
Subject [jira] Updated: (MAPREDUCE-2212) MapTask and ReduceTask should only compress/decompress the final map output file
Date Tue, 07 Dec 2010 19:57:10 GMT

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

Scott Chen updated MAPREDUCE-2212:
----------------------------------

    Description: 
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.

  was:
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 cause 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 do the compression only for the final map output file that is been transmit over
the network.


> 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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