[GitHub] [iceberg] flyrain commented on a diff in pull request #6002: Core: Add file seq number to ManifestEntry

[GitBox <gi...@apache.org>]

flyrain commented on code in PR #6002:
URL: https://github.com/apache/iceberg/pull/6002#discussion_r1006133472


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format/spec.md:
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@@ -463,8 +464,9 @@ When a file is added to the dataset, its manifest entry should store the snapsho
 
 When a file is replaced or deleted from the dataset, its manifest entry fields store the snapshot ID in which the file was deleted and status 2 (deleted). The file may be deleted from the file system when the snapshot in which it was deleted is garbage collected, assuming that older snapshots have also been garbage collected [1].
 
-Iceberg v2 adds a sequence number to the entry and makes the snapshot id optional. Both fields, `sequence_number` and `snapshot_id`, are inherited from manifest metadata when `null`. That is, if the field is `null` for an entry, then the entry must inherit its value from the manifest file's metadata, stored in the manifest list [2].
-The `sequence_number` field represents the data sequence number and must never change after a file is added to the dataset. 
+Iceberg v2 adds data and file sequence numbers to the entry and makes the snapshot ID optional. Values for these fields are inherited from manifest metadata when `null`. That is, if the field is `null` for an entry, then the entry must inherit its value from the manifest file's metadata, stored in the manifest list.
+The `sequence_number` field represents the data sequence number and must never change after a file is added to the dataset. The `file_sequence_number` field represents the sequence number of the snapshot that added the file and must also remain unchanged upon assigning at commit.

Review Comment:
   I feel a bit hard to understand the difference between them. Can we add something like, 
   ```
   The `sequence_number` will change when rewrite happens or metadata delete happens, but the `file_sequence_number` will never change.
   ```



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