gaborkaszab commented on code in PR #16425: URL: https://github.com/apache/iceberg/pull/16425#discussion_r4446570233
########## format/spec.md: ########## @@ -1801,6 +1804,40 @@ If a delete column in an equality delete file is later dropped from the table, i Manifests hold the same statistics for delete files and data files. For delete files, the metrics describe the values that were deleted. +### Column Files + +Starting in v4, a data file may store fields in column files listed in [`column_files`](#column-file-fields). A column file can use any supported Iceberg file format and must have rows that align with the data file it modifies. + +A column file is responsible for all the values of the fields listed in its `field_ids`. Each ID must identify a field in the table schema, or a row lineage field required by [Writing Column Files](#writing-column-files). A schema field must be top-level or nested in structs, and must not be nested within a list or map. + +#### Writing Column Files + +A column file stores the value of each of its listed fields for every row of the data file. Values that did not change are still included, and values for deleted rows should be null. + +When column files are added to a data file, the writer must produce a MODIFIED entry and a REPLACED entry as described in [Updating Tracking Metadata](#updating-tracking-metadata). The MODIFIED entry and the REPLACED entry may be written to different manifests. + +The `tracking` fields of the MODIFIED entry are set as described in [Updating Tracking Metadata](#updating-tracking-metadata) and [Sequence Number Inheritance](#sequence-number-inheritance), and `tracking.snapshot_id` must be the previous entry's (inherited) snapshot ID. The other fields of the MODIFIED entry must match the previous entry, except for the following: + +- `partition`: + - If an added column file lists a field that is, or contains, a source field of the data file's partition spec, every row that is not deleted must have the same partition values after the update, and `partition` must be set to those values. +- `sort_order_id`: + - If an added column file lists a field that is, or contains, a field in the sort order, `sort_order_id` must be null. +- `content_stats`: + - Stats for a field listed in an added column file, and for its nested fields, must be computed from that column file, or omitted. +- `tight_stats`: + - `tight_stats` must be false or omitted. +- `deletion_vector`: + - Every delete that applied to the data file before the column files were added must be written into the MODIFIED entry's `deletion_vector`. +- `column_files`: + - Each field ID listed in an added column file must be removed from the `field_ids` of the previous entry's column files, and a column file with no remaining `field_ids` must be removed. + - One new column file must list `_last_updated_sequence_number` in its `field_ids`, with a null value for rows the update changed and the row's current non-null value for other rows that are not deleted. Review Comment: For row lineage we need the LUSN coming from the latest column file. The general read algorithm is: 1) check if a field ID in the projection is covered by a column file 2) if yes, read it from that particular column file, 3) if no, read it from the base file. Including LUSN into the field IDs of the latest column file works well with the above algorithm. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
