The Table specification doesn't mention anything about requirements for whether writing identity partitioned columns is necessary. Empirically, it appears that implementations always write the column data at least for parquet. For columnar formats, this is relatively cheap as it is trivially RLE encodable. For Avro though it comes at a little bit of a higher cost. Since the data is fully reproducible from Iceberg metadata, I think stating this as optional in the specification would be useful.
For reading identity partitioned from Iceberg tables, I think the specification needs to require that identity partition column values are read from metadata. This is due to the fact that Iceberg supports migrating Hive data (and other table formats) without data rewrites that don't typically write their partition information directly into files. Thoughts? When we get consensus I'll open up a PR to clarify these points. Thanks, Micah
