Columnar binary metadata

Parquet, Arrow IPC / Feather, Avro, and ORC share flattened column statistics via ColumnarCommonFields.

Shared fields

Present on parquet_metadata, arrow_ipc_metadata, avro_metadata, and orc_metadata:

Field	Meaning
`row_count`, `column_count`, `stats_rows_sampled`, `columns`	See Column statistics
`encoding`	Text encoding when relevant

Block	Extra fields
`parquet_metadata`	`num_row_groups`
`arrow_ipc_metadata`	`container_kind` — `ipc_file`, `ipc_stream`, or `feather`
`avro_metadata`	`schema_canonical`
`orc_metadata`	`num_stripes`