[jira] [Created] (SPARK-3036) Add MapType containing null value support to Parquet.

["Takuya Ueshin (JIRA)" <ji...@apache.org>]

Takuya Ueshin created SPARK-3036:
------------------------------------

             Summary: Add MapType containing null value support to Parquet.
                 Key: SPARK-3036
                 URL: https://issues.apache.org/jira/browse/SPARK-3036
             Project: Spark
          Issue Type: Bug
          Components: SQL
            Reporter: Takuya Ueshin
            Priority: Blocker


Current Parquet schema for {{MapType}} is as follows regardless of {{valueContainsNull}}:

{noformat}
message root {
  optional group a (MAP) {
    repeated group map (MAP_KEY_VALUE) {
      required int32 key;
      required int32 value;
    }
  }
}
{noformat}

and if the map contains {{null}} value, it throws runtime exception.

To handle {{MapType}} containing {{null}} value, the schema should be as follows if {{valueContainsNull}} is {{true}}:

{noformat}
message root {
  optional group a (MAP) {
    repeated group map (MAP_KEY_VALUE) {
      required int32 key;
      optional int32 value;
    }
  }
}
{noformat}

FYI:
Hive's Parquet writer *always* uses the latter schema, but reader can read from both schema.

NOTICE:
This change will break backward compatibility when the schema is read from Parquet metadata ({{"org.apache.spark.sql.parquet.row.metadata"}}).




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