I looked at the Iceberg Data API <https://github.com/apache/iceberg/tree/master/data/src/main/java/org/apache/iceberg/data> and found that the write is row based. If I want to use a columnar data file format like Parquet and efficiently sink columnar data in memory (like Arrow). I assume it is not currently implemented but OK to enhance the data API to support this?
-- Chen Song
