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From Jiayu Ji <jiayu...@gmail.com>
Subject Re: How does mapreduce job determine the compress codec
Date Mon, 16 Dec 2013 15:29:09 GMT
Thanks Azurry. That was exactly the thing I want to know.


On Sun, Dec 15, 2013 at 7:53 PM, Azuryy Yu <azuryyyu@gmail.com> wrote:

> Hi Jiayu,
> For the Sequence file as an input, CompressCodec class was serialized in
> the file header, then Sequence Filereader will know the compression algo.
> thanks.
>
>
>
>
> On Mon, Dec 16, 2013 at 8:28 AM, Jiayu Ji <jiayu.ji@gmail.com> wrote:
>
>> Thanks Tao. I know I can tell it is a lzo file based on the magic number.
>> What I am curious is which class in hadoop used by the mapreduce job to
>> determine the file compression algorithm. At the end of the day, I am
>> trying to figure out whether all the inputs of a mapreduce job have to be
>> compressed with the same algorithm.
>>
>>
>> On Fri, Dec 13, 2013 at 11:16 PM, Tao Xiao <xiaotao.cs.nju@gmail.com>wrote:
>>
>>> I suggest you download the lzo compressed file, no matter weather it has
>>> a lzo extension as its file name,  and open it in the form of hex bytes
>>> with tools like UltraEdit, and have a look at its heading contents.
>>>
>>>
>>> 2013/12/14 Jiayu Ji <jiayu.ji@gmail.com>
>>>
>>>> Hi
>>>>
>>>> I am having this question on how does mapreduce job determine the
>>>> compress codec on hdfs. From what I read on the definitive guide (page
>>>> 86)," the CompressionCodecFactory provides a way of mapping a filename
>>>> extension to a CompressionCodec using its getCodec() method". I did a test
>>>> with a lzo compressed file without a lzo extension. However, the mapreduce
>>>> job was still able to get the right codec. Does anyone know why? Thanks in
>>>> advance.
>>>>
>>>> Jiayu
>>>>
>>>
>>>
>>
>>
>> --
>> Jiayu (James) Ji,
>>
>> Cell: (312)823-7393
>>
>>
>


-- 
Jiayu (James) Ji,

Cell: (312)823-7393

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