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From Kim Chew <kchew...@gmail.com>
Subject Re: Why is HDFS_BYTES_WRITTEN is much larger than HDFS_BYTES_READ in this case?
Date Thu, 27 Mar 2014 20:34:14 GMT
I am also wondering if, say, I have two identical timestamp so they are
going to be written to the same file. Does MulitpleOutputs handle appending?

Thanks.

Kim


On Thu, Mar 27, 2014 at 12:30 PM, Thomas Bentsen <th@bentzn.com> wrote:

> Have you checked the content of the files you write?
>
>
> /th
>
> On Thu, 2014-03-27 at 11:43 -0700, Kim Chew wrote:
> > I have a simple M/R job using Mapper only thus no reducer. The mapper
> > read a timestamp from the value, generate a path to the output file
> > and writes the key and value to the output file.
> >
> >
> > The input file is a sequence file, not compressed and stored in the
> > HDFS, it has a size of 162.68 MB.
> >
> >
> > Output also is written as a sequence file.
> >
> >
> >
> > However, after I ran my job, I have two output part files from the
> > mapper. One has a size of 835.12 MB and the other has a size of 224.77
> > MB. So why is the total outputs size is so much larger? Shouldn't it
> > be more or less equal to the input's size of 162.68MB since I just
> > write the key and value passed to mapper to the output?
> >
> >
> > Here is the mapper code snippet,
> >
> > public void map(BytesWritable key, BytesWritable value, Context
> > context) throws IOException, InterruptedException {
> >
> >         long timestamp = bytesToInt(value.getBytes(),
> > TIMESTAMP_INDEX);;
> >         String tsStr = sdf.format(new Date(timestamp * 1000L));
> >
> >         mos.write(key, value, generateFileName(tsStr)); // mos is a
> > MultipleOutputs object.
> >     }
> >
> >         private String generateFileName(String key) {
> >         return outputDir+"/"+key+"/raw-vectors";
> >     }
> >
> >
> > And here are the job outputs,
> >
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Launched map tasks=2
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Data-local map tasks=2
> > 14/03/27 11:00:56 INFO mapred.JobClient:     SLOTS_MILLIS_REDUCES=0
> > 14/03/27 11:00:56 INFO mapred.JobClient:   File Output Format
> > Counters
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Bytes Written=0
> > 14/03/27 11:00:56 INFO mapred.JobClient:   FileSystemCounters
> > 14/03/27 11:00:56 INFO mapred.JobClient:     HDFS_BYTES_READ=171086386
> > 14/03/27 11:00:56 INFO mapred.JobClient:     FILE_BYTES_WRITTEN=54272
> > 14/03/27 11:00:56 INFO mapred.JobClient:
> > HDFS_BYTES_WRITTEN=1111374798
> > 14/03/27 11:00:56 INFO mapred.JobClient:   File Input Format Counters
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Bytes Read=170782415
> > 14/03/27 11:00:56 INFO mapred.JobClient:   Map-Reduce Framework
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Map input records=547
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Physical memory (bytes)
> > snapshot=166428672
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Spilled Records=0
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Total committed heap
> > usage (bytes)=38351872
> > 14/03/27 11:00:56 INFO mapred.JobClient:     CPU time spent (ms)=20080
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Virtual memory (bytes)
> > snapshot=1240104960
> > 14/03/27 11:00:56 INFO mapred.JobClient:     SPLIT_RAW_BYTES=286
> > 14/03/27 11:00:56 INFO mapred.JobClient:     Map output records=0
> >
> >
> > TIA,
> >
> >
> > Kim
> >
>
>
>

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