[jira] [Created] (ARROW-6149) [Parquet] Decimal comparisons used for min/max statistics are not correct

["Philip Felton (JIRA)" <ji...@apache.org>]

Philip Felton created ARROW-6149:
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             Summary: [Parquet] Decimal comparisons used for min/max statistics are not correct
                 Key: ARROW-6149
                 URL: https://issues.apache.org/jira/browse/ARROW-6149
             Project: Apache Arrow
          Issue Type: Bug
            Reporter: Philip Felton


The [https://github.com/apache/parquet-format/blob/master/LogicalTypes.md|Parquet Format specifications] says

bq. If the column uses int32 or int64 physical types, then signed comparison of the integer values produces the correct ordering. If the physical type is fixed, then the correct ordering can be produced by flipping the most-significant bit in the first byte and then using unsigned byte-wise comparison.

However this isn't followed in the C++ Parquet code. 16-byte decimal comparison is implemented using a lexicographical comparison of signed chars.

This appears to be because the function [https://github.com/apache/arrow/blob/master/cpp/src/parquet/statistics.cc#L183] just goes off the sort_order (signed) and physical_type (FIXED_LENGTH_BYTE_ARRAY), there is no override for decimal.



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