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  1. Pig
  2. PIG-3952

PigStorage accepts '-tagSplit' to return full split information



    • Improvement
    • Status: Patch Available
    • Major
    • Resolution: Unresolved
    • None
    • None
    • internal-udfs
    • Patch Available
    • The -tagSplit option to PigStorage causes it to prepend the full file split information (full path, split index, split offset and split length, all separated by hash ('#') marks) to each Tuple/row as it's loaded


      If <code>-tagSplit</code> is specified, PigStorage will prepend the full file split information, separated by hash ('#') marks, to each Tuple/row:

      • File path (directory and filename) of the split
      • Split index (zero-based)
      • Split offset: starting position of the split in bytes.
      • Split length: length of the split in bytes.

      Motivating examples are

      • attach a unique ordered ID without a reduce: with the split index and sequentially numbered files (or some other strict ordering of the filenames) you can build a serial ID from say SPRINTF("%05d-%3d-%8d", (int)file_idx, (int)split_idx, rank_vals).
      • do a consistent shuffle; the lines will be well-mixed but remain identically shuffled from run to run. With a seedable hash function you can stabilize the mixing for testing purposes.
      -- shuffle according to a hash with good mixing properties. MD5 is OK but  murmur3 from DATAFU-47 even better.
      DEFINE Hasher datafu.pig.hash.MD5('hex');
      vals = LOAD '/data/geo/us_city_pops.tsv' USING PigStorage('\t', '-tagSplit')
        AS (split_info:chararray, city:chararray, state:chararray, pop:int);
      vals_rked = RANK vals;
      vals_ided = FOREACH vals_rked {
        line_info = CONCAT((chararray)split_info, '#', (chararray)rank_vals);
        GENERATE Hasher((chararray)line_info) AS rand_id, *; 
      vals_shuffled = FOREACH (ORDER vals_ided BY rand_id) GENERATE *;
      STORE vals_shuffled INTO '/data/out/vals_shuffled';
      -- 7b86bdc8f28edb05025a556c06805753        37      file:/data/geo/census/us_city_pops.tsv#0#0#1541    Kansas City             Missouri         463202
      -- 7c9c93658545d5aba2825699866cb024        13      file:/data/geo/census/us_city_pops.tsv#0#0#1541    Austin                  Texas            820611
      -- 8532dc8d18992a688621950c50b6ca80        14      file:/data/geo/us_city_pops.tsv#0#0#1541    San Francisco           California       812826
      -- 8d8632fecb4895288f1684c451a01a0b        29      file:/data/geo/us_city_pops.tsv#0#0#1541    Portland                Oregon           593820




            Unassigned Unassigned
            mrflip Flip Kromer
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