Support for Map type in Parquet/Hive source and sinks

[hannesmiller]

• This equates to the Parquet org.apache.parquet.schema.OriginalType.MAP nested type - see https://github.com/apache/parquet-format/blob/master/LogicalTypes.md
• The following example demonstrates the type for a non-null map from strings to nullable integers:

// Map<String, Integer> required group my_map (MAP) { repeated group key_value { required binary key (UTF8); optional int32 value; } }

• Note like the Array support the value type could be any primitive or structured type.

• The following describe how to query structured types in Impala and HiveQL respectively:

https://www.cloudera.com/documentation/enterprise/5-5-x/topics/impala_complex_types.html https://joshuafennessy.com/2015/07/09/introduction-to-hive-complex-data-types-part-1-array/

[sksamuel]

Duplicate of #189