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...@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....@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...@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 > >
