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  1. IMPALA
  2. IMPALA-5628 Parquet support for additional valid decimal representations
  3. IMPALA-2515

Impala rejects Parquet schemas where decimal fixed_len_byte_array columns have unnecessary padding bytes

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Details

    • Sub-task
    • Status: Resolved
    • Minor
    • Resolution: Fixed
    • Impala 2.3.0
    • Impala 4.0.0
    • Backend

    Description

      Impala cannot read this:

      {"name": "tmp_1",
       "type": "fixed",
       "size": 8,
       "logicalType": "decimal",
       "precision": 10,
       "scale": 5}
      

      However, this can be read:

      {"name": "tmp_1",
       "type": "fixed",
       "size": 5,
       "logicalType": "decimal",
       "precision": 10,
       "scale": 5}
      

      Size must be precisely set to this, or Impala is unable to read the decimal column:

      size = int(math.ceil((math.log(2, 10) + precision) / math.log(256, 10)))
      

      There is nothing in the Parquet spec that says that Decimal columns must be sized precisely. Arguably it's a bug in the writer if it's doing it, because it's just wasting space.
      https://github.com/apache/parquet-format/blob/master/LogicalTypes.md#decimal

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          Onur Tokat
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          Onur Tokat
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          Onur Tokat
        6. image-2020-02-07-11-48-35-179.png
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          Onur Tokat

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            tarmstrong Tim Armstrong
            tarasbob Taras Bobrovytsky
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              Updated:
              Resolved:

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