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  1. Hadoop Common
  2. HADOOP-5539

o.a.h.mapred.Merger not maintaining map out compression on intermediate files



    • Bug
    • Status: Resolved
    • Blocker
    • Resolution: Fixed
    • 0.19.1
    • 0.20.1
    • None
    • None
    • 0.19.2-dev, r753365

    • Reviewed


      hadoop-site.xml :
      mapred.compress.map.output = true

      map output files are compressed but when the in memory merger closes
      on the reduce the on disk merger runs to reduce input files to <= io.sort.factor if needed.

      when this happens it outputs files called intermediate.x files these
      do not maintain compression setting the writer (o.a.h.mapred.Merger.class line 432)
      passes the codec but I added some logging and its always null map output compression set true or false.

      This causes task to fail if they can not hold the uncompressed size of the data of the reduce its holding
      I thank this is just and oversight of the codec not getting set correctly for the on disk merges.

      2009-03-20 01:30:30,005 INFO org.apache.hadoop.mapred.Merger: Merging 30 intermediate segments out of a total of 3000
      2009-03-20 01:30:30,005 INFO org.apache.hadoop.mapred.Merger: intermediate.1 used codec: null

      I added

                // added my me
      	   if (codec != null){
      	     LOG.info("intermediate." + passNo + " used codec: " + codec.toString());
      	   } else {
      	     LOG.info("intermediate." + passNo + " used codec: Null");
      	   // end added by me

      Just before the creation of the writer o.a.h.mapred.Merger.class line 432
      and it outputs the second line above.

      I have confirmed this with the logging and I have looked at the files on the disk of the tasktracker. I can read the data in
      the intermediate files clearly telling me that there not compressed but I can not read the map.out files direct from the map output
      telling me the compression is working on the map end but not on the on disk merge that produces the intermediate.

      I can see no benefit for these not maintaining the compression setting and as it looks they where intended to maintain it.


        1. hadoop-5539-branch20.patch
          4 kB
          Jothi Padmanabhan
        2. hadoop-5539-v1.patch
          5 kB
          Jothi Padmanabhan
        3. hadoop-5539.patch
          6 kB
          Jothi Padmanabhan
        4. 5539.patch
          5 kB
          Billy Pearson



            jothipn Jothi Padmanabhan
            viper799 Billy Pearson
            1 Vote for this issue
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