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  1. Parquet
  2. PARQUET-1217

Incorrect handling of missing values in Statistics

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Details

    • Bug
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 1.5.0, 1.6.0, 1.7.0, 1.8.0, 1.9.0, 1.10.0
    • 1.10.0, 1.8.3
    • None
    • None

    Description

      As per the parquet-format specs the min/max values in statistics are optional. Therefore, it is possible to have numNulls in Statistics while we don't have min/max values. In StatisticsFilter we rely on the method StatisticsFilter.isAllNulls(ColumnChunkMetaData) to handle the case of null min/max values which is not correct due to the described scenario.
      We shall check Statistics.hasNonNullValue() any time before using the actual min/max values.

      In addition we don't check if the null_count is set or not when reading from the parquet file. We simply use the value which is 0 in case of unset. In the parquet-mr side the Statistics object uses the value 0 to sign that the num_nulls is unset. It is incorrect if we are searching for null values and we falsely drop a column chunk thinking there are no null values but the field in the statistics was simply unset.

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              gszadovszky Gabor Szadovszky
              gszadovszky Gabor Szadovszky
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