flyrain commented on code in PR #4945:
URL: https://github.com/apache/iceberg/pull/4945#discussion_r905420869
##########
format/spec.md:
##########
@@ -486,16 +486,17 @@ When reading v1 manifests with no sequence number column,
sequence numbers for a
A snapshot consists of the following fields:
-| v1 | v2 | Field | Description |
-| ---------- | ---------- | ------------------------ | ----------- |
-| _required_ | _required_ | **`snapshot-id`** | A unique long ID |
-| _optional_ | _optional_ | **`parent-snapshot-id`** | The snapshot ID of the
snapshot's parent. Omitted for any snapshot with no parent |
-| | _required_ | **`sequence-number`** | A monotonically
increasing long that tracks the order of changes to a table |
-| _required_ | _required_ | **`timestamp-ms`** | A timestamp when the
snapshot was created, used for garbage collection and table inspection |
-| _optional_ | _required_ | **`manifest-list`** | The location of a
manifest list for this snapshot that tracks manifest files with additional
metadata |
-| _optional_ | | **`manifests`** | A list of manifest file
locations. Must be omitted if `manifest-list` is present |
-| _optional_ | _required_ | **`summary`** | A string map that
summarizes the snapshot changes, including `operation` (see below) |
-| _optional_ | _optional_ | **`schema-id`** | ID of the table's
current schema when the snapshot was created |
+| v1 | v2 | Field | Description
|
+| ---------- | ---------- | ------------------------
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| _required_ | _required_ | **`snapshot-id`** | A unique long ID
|
+| _optional_ | _optional_ | **`parent-snapshot-id`** | The snapshot ID of the
snapshot's parent. Omitted for any snapshot with no parent
|
+| | _required_ | **`sequence-number`** | A monotonically
increasing long that tracks the order of changes to a table
|
+| _required_ | _required_ | **`timestamp-ms`** | A timestamp when the
snapshot was created, used for garbage collection and table inspection
|
+| _optional_ | _required_ | **`manifest-list`** | The location of a
manifest list for this snapshot that tracks manifest files with additional
metadata |
+| _optional_ | | **`manifests`** | A list of manifest file
locations. Must be omitted if `manifest-list` is present
|
+| _optional_ | _required_ | **`summary`** | A string map that
summarizes the snapshot changes, including `operation` (see below)
|
+| _optional_ | _optional_ | **`schema-id`** | ID of the table's
current schema when the snapshot was created
|
+| _optional_ | _optional_ | **`statistics`** | A [statistics file's
metadata](#statistics-file). The field should be retained by writers, unless
writer updates the statistics, or knows they became obsolete. |
Review Comment:
If there is only one statistics file per table, we can have it in [Table
metadata](https://iceberg.apache.org/spec/#table-metadata) instead of
[snapsthots](https://iceberg.apache.org/spec/#snapshots).
Is there a link why we want only one statistics file per table? I assume
per-snapshot one makes more sense. For example, we can remove the statistics
files of a snapshot when we expire the snapshot.
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