RussellSpitzer commented on code in PR #11130:
URL: https://github.com/apache/iceberg/pull/11130#discussion_r1779126152
##########
format/spec.md:
##########
@@ -298,16 +298,101 @@ Iceberg tables must not use field ids greater than
2147483447 (`Integer.MAX_VALU
The set of metadata columns is:
-| Field id, name | Type | Description |
-|-----------------------------|---------------|-------------|
-| **`2147483646 _file`** | `string` | Path of the file in which a
row is stored |
-| **`2147483645 _pos`** | `long` | Ordinal position of a row in
the source data file |
-| **`2147483644 _deleted`** | `boolean` | Whether the row has been
deleted |
-| **`2147483643 _spec_id`** | `int` | Spec ID used to track the file
containing a row |
-| **`2147483642 _partition`** | `struct` | Partition to which a row
belongs |
-| **`2147483546 file_path`** | `string` | Path of a file, used in
position-based delete files |
-| **`2147483545 pos`** | `long` | Ordinal position of a row,
used in position-based delete files |
-| **`2147483544 row`** | `struct<...>` | Deleted row values, used in
position-based delete files |
+| Field id, name | Type | Description
|
+|----------------------------------|---------------|---------------------------------------------------------------------------------------------------------|
+| **`2147483646 _file`** | `string` | Path of the file in which
a row is stored |
+| **`2147483645 _pos`** | `long` | Ordinal position of a row
in the source data file, starting at `0` |
+| **`2147483644 _deleted`** | `boolean` | Whether the row has been
deleted |
+| **`2147483643 _spec_id`** | `int` | Spec ID used to track the
file containing a row |
+| **`2147483642 _partition`** | `struct` | Partition to which a row
belongs |
+| **`2147483546 file_path`** | `string` | Path of a file, used in
position-based delete files
|
+| **`2147483545 pos`** | `long` | Ordinal position of a
row, used in position-based delete files
|
+| **`2147483544 row`** | `struct<...>` | Deleted row values, used
in position-based delete files |
+| **`2147483543 _row_id`** | `long` | A unique long assigned
when row-lineage is enabled see [Row Lineage](#row-lineage)
|
+| **`2147483542 _last_update`** | `long` | The sequence number which
last updated this row when row-lineage is enabled [Row Lineage](#row-lineage) |
+
+### Row Lineage
+
+In v3 and later, an Iceberg table can track row lineage fields for all newly
created rows. Row lineage is enabled by setting the field `row-lineage` to
true in the table's metadata. When enabled, engines must maintain the
`next-row-id` table field and the following row-level fields when writing data
files:
+
+* `_row_id` a unique long for every row. Assigned via inheritance when a row
is added and the existing value is explicitly written when the row is written
to a new file.
+* `_last_update` the sequence number of the commit that last updated a row.
The value is inherited when a row is added or modified and the existing value
is explicitly written when the row is written to a different data file but not
modified.
+
+These fields are assigned and updated by inheritance because the commit
sequence number and starting row ID are not assigned until the snapshot is
successfully committed. Inheritance is used to allow writing data and manifest
files before values are known so that it is not necessary to rewrite data and
manifest files when an optimistic commit is retried.
+
+When row lineage is enabled, new snapshots cannot include [Equality
Deletes](#equality-delete-files). Row lineage is incompatible with equality
deletes because lineage values must be maintained, but equality deletes are
used to avoid reading existing data before writing changes.
+
+
+#### Row lineage assignment
+
+Row lineage fields are written when row lineage is enabled. When not enabled,
row lineage fields (`_row_id` and `_last_update`) must not be written to data
files. The rest of this section applies when row lineage is enabled.
Review Comment:
I think disabling is allowed it just means we stop changing any of the
metadata and lineage information may be possibly lost by clients which don't
support row-lineage. I don't think we need to prevent this.
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