hubgeter opened a new pull request, #68331:
URL: https://github.com/apache/doris/pull/68331
### What problem does this PR solve?
Issue Number: None
Related PR: #68214
Problem Summary:
`retainPredicatePathsInFinalAllAccessPaths`, added by #68214, removes every
predicate access path that is not literally one of the final all access paths.
That is what NULL/OFFSET paths need, because they are stripped from the all
paths on purpose, but it also removes ordinary sub-field paths whenever the all
paths collapse to the whole-column path:
```sql
SELECT s FROM tbl WHERE struct_element(s, 'city') = 'x';
-- all access paths: [s], predicate access paths: [] (was [s.city])
```
BE then cannot tell which sub-column the predicate reads, so it loses the
eager/lazy split and reads the column as one unit. On branch-4.2 this shows up
in `test_iceberg_variant_read`, where the lazy-read check sees
`FilteredRowsByLazyRead = 0` for
```sql
SELECT CAST(v AS STRING) FROM variant_page_pruning WHERE CAST(v['n'] AS INT)
> 3000
```
Only file scans hit this: on OLAP tables a variant sub-path predicate gets
its own sub-column slot, so its all paths already contain the predicate path.
That is why the existing unit tests did not catch it, and why the new test uses
a struct column, which keeps one slot for the whole column.
This PR keeps the NULL/OFFSET cleanup, since BE switches the whole iterator
to `NULL_MAP_ONLY`/`OFFSET_ONLY` once such a path shows up and skips the
children. Every other predicate path is kept, and added to the all paths when
no wider path covers it — the behaviour of master's
`addPredicatePathsToFinalAllAccessPaths`.
### Release note
Fix nested/variant sub-field predicates losing lazy materialization on
branch-4.2 when the whole column is read.
### Check List (For Author)
- Test
- [ ] Regression test
- [x] Unit Test
- [ ] Manual test (add detailed scripts or steps below)
- [ ] No need to test or manual test. Explain why:
- [ ] This is a refactor/code format and no logic has been changed.
- [ ] Previous test can cover this change.
- [ ] No code files have been changed.
- [ ] Other reason
- Behavior changed:
- [ ] No.
- [x] Yes. Sub-field predicates keep their access paths, restoring
predicate-first reads.
- Does this need documentation?
- [x] No.
- [ ] Yes.
### Check List (For Reviewer who merge this PR)
- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label
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