RussellSpitzer commented on code in PR #11130:
URL: https://github.com/apache/iceberg/pull/11130#discussion_r1779115055
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format/spec.md:
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@@ -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:
Every "row_id" can be used to track the creation of a row by checking the
"row_id" high water mark of each snapshot in the table history. This allows a
user (with sufficent snapshot history) to determine when any particular row was
initially added to the table. The second field `last-updated-seq` points to the
update in which the row was last modified.
Together these allow you determine when a row was made and when it was last
changed. The origin of a modified row is always the row with the exact same
`_row_id` in the commit before `last-updated-seq`.
Impact on read should be 0 since these columns do not need to actually be
materialized by scans. Impact on merge statements/copy statements should be
slightly increased because more data has to go through the compute engine
although this will differ in efficiency based on the engine.
On file size this should be relatively low impact but we can do some
benchmarks once the reference implementation is done. For use cases without
row-level-updates it would be very very cheap since any materialized `row_id`
and `last-updated-sequence` values should be either very very similar (and
compressible) or identical.
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