jackye1995 commented on a change in pull request #3425:
URL: https://github.com/apache/iceberg/pull/3425#discussion_r755734292
##########
File path: site/docs/spec.md
##########
@@ -548,6 +548,21 @@ Notes:
1. An alternative, *strict projection*, creates a partition predicate that
will match a file if all of the rows in the file must match the scan predicate.
These projections are used to calculate the residual predicates for each file
in a scan.
2. For example, if `file_a` has rows with `id` between 1 and 10 and a delete
file contains rows with `id` between 1 and 4, a scan for `id = 9` may ignore
the delete file because none of the deletes can match a row that will be
selected.
+#### Snapshot Reference
+
+Snapshot reference allows users to perform tagging and branching within an
Iceberg table. The detailed user experience is described in [Iceberg Tagging
and Branching](../snapshot-tag-branch).
+
+The snapshot reference object records all the user-defined information of a
snapshot including name, reference type and retention policy configurations.
+
+| v2 | Field name | Type | Description |
+| ---------- |------------------------------|-----------|-------------|
+| _required_ | **`snapshot-id`** | `long` | The ID of the
snapshot referenced |
+| _required_ | **`name`** | `string` | The name of the
reference |
+| _required_ | **`type`** | `string` | Type of the
reference, `tag` or `branch` |
+| _optional_ | **`min-snapshots-to-keep`** | `int` | For `branch` type
only, the minimum number of snapshots to keep in a branch |
+| _required_ | **`max-snapshot-age-ms`** | `long` | The duration before
a snapshot tagged or in a branch could be expired by any automatic snapshot
expiration process |
Review comment:
@rdblue good point, I was defaulting to the table default by setting it
to 5 days explicitly so in the spec it is required.
I agree it sounds better to inherit the table's latest value of
`history.expire.max-snapshot-age-ms`, although the retention would change if
user updates the table property, that is likely the expected behavior, similar
to how metrics mode is configured for the whole table and inherited for each
column. I will make the change.
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