leborchuk commented on PR #1762:
URL: https://github.com/apache/cloudberry/pull/1762#issuecomment-4810240769
### 2. Shared Scan Column Pruning
LGTM, while at the beginning, I was confused by the number of fixes needed
to make it work. However, after thorough investigation and reading, I think
that remapping columns using `change_varattnos_of_ShareInputScan()` is quite
safe, and there is no need for additional GUC protection. We could simply fix
all issues if there were only one left.
Initially I started with commit 54930251e4c but there is nothing it's
preparing commit for further improvements
Commit | Date | Subject | Note
-- | -- | -- | --
54930251e4c | 2025-10-27 | Insert Result node atop CTE producer for column
projection optimization | The message describes exactly this feature, but the
actual diff does not implement Result-node insertion or column pruning. It only
refactors Shared Scan predicate-pushdown control flow. Treat it as misleading /
not the implementation commit.
The main work is done there
Commit | Date | Subject | Note
-- | -- | -- | --
abbb9469062 | 2025-11-28 | Implement Shared Scan column pruning. | This is
the commit that actually implements the feature described: tracking used CTE
consumer columns, building an attribute mapping, inserting a producer-side
projection, and remapping consumer target lists.
The fixes in logic
Commit | Date | Subject | Note
-- | -- | -- | --
065983a1e69 | 2025-12-05 | Fix NULL check for CTE attribute map in setrefs |
Fixes null handling around the CTE attribute map introduced by pruning.
a2711ef5ac9 | 2026-01-02 | Fix Shared Scan target list varattno adjustment |
Fixes attribute-number remapping after pruning.
31c97bfee5a | 2026-01-02 | Fix ShareInputScan target list construction |
Fixes target-list construction for Shared Scan after projection changes.
51b3f681a03 | 2026-01-03 | Fix logic for correcting Shared Scan target list
varattno | Further fixes varattno correction logic.
fdd9e8fee2b | 2026-01-03 | Fix assertion for subquery unused column handling
| Fixes assertion failures around unused/pruned columns.
b2cf7a4f0fb | 2026-01-08 | Handle whole-row references in Shared Scan
projection | Handles cases like selecting the whole CTE row, where pruning
cannot safely remove columns.
d8c98164156 | 2026-01-09 | Remove unnecessary nodes from SharedScan subquery
| Cleans up unnecessary nodes after the Shared Scan projection work.
I didn't check all of them using gdb, so I cannot say that they actually
fixed all the issues that were described. I just read the description and
checked the logic and saw no issues. We gradually came to a solution when
everything perform inside `change_varatnos_of_shareinputscan()` and so we just
needed not to forget that `varatno == 0` was a special case for `select
table.*` and that we needed to replace only references related to the shared
CTE, not any matching references.
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