stevenzwu commented on code in PR #11130:
URL: https://github.com/apache/iceberg/pull/11130#discussion_r1774095086


##########
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:
    If I understand this correctly, the purpose is to keep the same `_row_id` 
during file rewrites like compaction, sorting.  should we just call this `Row 
Identifier`? `Lineage` typically means changes/updates on the rows with primary 
key (as defined by `Identifier fields`).



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