aokolnychyi opened a new pull request, #49493:
URL: https://github.com/apache/spark/pull/49493
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### What changes were proposed in this pull request?
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This PR introduces conditional nullification of metadata columns in DELETE,
UPDATE, and MERGE operations. Previously, connectors could request a set of
metadata columns to be projected in a row-level operation, but the metadata
values were always preserved and could not be nullified. With this change,
connectors control which metadata columns should be preserved or nullified
during deletion or modification.
The new behavior is implemented via flags in `metadataInJSON` exposed for
`MetadataAttribute`, similar to what we do for data columns in DSv2.
### Why are the changes needed?
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These changes are essential to support row lineage in Iceberg and Delta
Lake. Both projects define a row ID and a row version as part of their metadata
concepts. The row ID is a synthetic metadata column that is initially null when
a record is first inserted and becomes assigned through inheritance. Once
assigned, the row ID must remain constant and unaltered. In contrast, the row
version is updated with every modification and must be re-assigned. The
existing implementation of DELETE, UPDATE, and MERGE operations doesn't support
conditional metadata column nullification required to support row lineage.
Suppose there is a table containing the following rows:
```
dep | name | salary | _row_lineage_id | _row_lineage_version |
_file | _pos
-----+-----------+--------+-----------------+----------------------+----------------+------
hr | Alice | 200 | 101 | v1 |
fileA.parquet | 0
hr | Robert | 240 | 102 | v1 |
fileA.parquet | 1
it | Charlie | 260 | 103 | v1 |
fileA.parquet | 2
it | Bob | 220 | 104 | v1 |
fileA.parquet | 3
```
Then `UPDATE t SET salary = salary + 10 WHERE dep = 'hr'` should produce:
```
operation | row_id (_file, _pos) | row (dep, name, salary) |
metadata (_row_lineage_id, _row_lineage_version)
-----------+-----------------------------+--------------------------+-----------------------------------------------
update | (fileA.parquet, 0) | (hr, Alice, 210) | (1,
null)
update | (fileA.parquet, 1) | (hr, Robert, 250) | (2,
null)
```
Note that `_row_lineage_id` values are preserved but `_row_lineage_version`
are nullified.
### Does this PR introduce _any_ user-facing change?
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Yes, but the changes are backward compatible due to default values.
### How was this patch tested?
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This PR comes with unit tests.
### Was this patch authored or co-authored using generative AI tooling?
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No.
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