I think we should change TableDescriptor to have a single TYPE_STRUCT root type_, which will replace the current vector<ColumnDescriptor> col_descs_. This will make it easier to traverse nested schemas, as we won't have to special-case the table-level columns, and is more inline with Table in the FE. In particular I think this will make it easier to unit-test schema resolution functions in the parquet scanner.
If no one objects, I'll go ahead and start working on a patch for this.
