[ARROW-10514] [C++][Parquet] Data inconsistency in parquet-reader output modes

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 4.0.0
• Component/s: C++
• Labels: pull-request-available
• Flags: Patch
• External issue URL: https://github.com/apache/arrow/issues/26483
• Assignee: Zosimova Zhanna
• Reporter: Zosimova Zhanna
• Created: 07/Nov/20 18:46
• Updated: 11/Jan/23 08:13
• Resolved: 10/Mar/21 13:14

Description

I tried reading description for Parquet file with nested maps using parquet-reader tool. 

This file has the following structure:

required group field_id=0 spark_schema {
  optional group field_id=1 a (Map) {
    repeated group field_id=2 key_value {
      required binary field_id=3 key (String);
      optional group field_id=4 value (Map) {
        repeated group field_id=5 key_value {
          required int32 field_id=6 key;
          required boolean field_id=7 value;
        }
      }
    }
  }
  required int32 field_id=8 b;
  required double field_id=9 c;
} 

When I print it using DebugPrint, I see:

$ ./parquet-reader nested_maps.snappy.parquet --only-metadata
<some text is omitted for the sake of readability>
Column 0: a.key_value.key (BYTE_ARRAY/UTF8)
Column 1: a.key_value.value.key_value.key (INT32)
Column 2: a.key_value.value.key_value.value (BOOLEAN)
Column 3: b (INT32)
Column 4: c (DOUBLE)
</some text is omitted for the sake of readability>

When I pring it using JSONPrint, I see:

$ ./parquet-reader nested_maps.snappy.parquet --json
<some text is omitted for the sake of readability>
"Columns": [
  { "Id": "0", "Name": "key", "PhysicalType": "BYTE_ARRAY", "ConvertedType": "UTF8", "LogicalType": {"Type": "String"} },
  { "Id": "1", "Name": "key", "PhysicalType": "INT32", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
  { "Id": "2", "Name": "value", "PhysicalType": "BOOLEAN", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
  { "Id": "3", "Name": "b", "PhysicalType": "INT32", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
  { "Id": "4", "Name": "c", "PhysicalType": "DOUBLE", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} }
]
</some text is omitted for the sake of readability>

Column 0 and Column 1 has the same Name in JSON output. That's very confusing. It would be more correct to output the full path of the column (key -> a.key_value.key).

 

This issue can be corrected by changing a single line: https://github.com/apache/arrow/blob/master/cpp/src/parquet/printer.cc#L218

 

The proposed patch in the attachment

Issue Links

• links to: GitHub Pull Request #9649