ashvina commented on code in PR #11130:
URL: https://github.com/apache/iceberg/pull/11130#discussion_r1774518287
##########
format/spec.md:
##########
@@ -298,16 +298,143 @@ 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
Review Comment:
(I’m not sure if the lineage proposal document is still active for
discussion, hence posting this comment here. If it is preferred, I can move
this discussion there.)
The term row lineage has limited scope -- it refers to a "sequence number"
which indicates when a row was created or modified. However, it does not
reference the source of a modified row. I.e. it does not provide details about
evolution of a row (the original row which was modified). Is this definition of
"evolution" sufficient?
Also, the proposal document mentions that the impact on reads should be
minimal. If there are any available metrics, specially increase in data file
size, it might be beneficial to include them in this document so that users can
understand the impact of enabling this feature.
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