CuteChuanChuan opened a new pull request, #26203:
URL: https://github.com/apache/datafusion/pull/26203
## Which issue does this PR close?
- Closes #25332 .
## Rationale for this change
`MapOffset` was a `(usize, Option<u64>)` tuple that encoded the resume point
of chunked hash map lookups by convention. One position had two encodings
(`(row, Some(0))` and `(row + 1, None)`), the unique-key fast paths read only
`offset.0`, and `HashJoinStream` relied on an undocumented invariant (`offset
== (0, None)` only before the first chunk).
## What changes are included in this PR?
- Replace the tuple with `pub enum ProbeOffset { AtRow { row }, MidChain {
row, next } }` in `join_hash_map.rs`, re-exported from `joins::utils` next to
`JoinHashMapType`.
- Normalize at the producer: `traverse_chain` returns `AtRow { row: row + 1
}` once a row's chain is finished, so every position has one encoding and
readers no longer handle `Some(0)`.
| Old | New |
|---|---|
| `(row, None)` | `AtRow { row }` |
| `(row, Some(next))`, `next != 0` | `MidChain { row, next }` |
| `(row, Some(0))` | `AtRow { row: row + 1 }` |
- Unique-key fast paths (`JoinHashMap`, `ArrayMap`) `debug_assert!` that
they only receive `AtRow`. This holds because `unique` is fixed when the build
side is built, and every chunk of a probe batch uses the same map.
- Add `ProcessProbeBatchState::is_first_chunk()` and use it at the three
first-chunk checks. The invariant it relies on (a returned offset is never
`AtRow { row: 0 }`) is documented on `ProbeOffset`.
## What is the testing strategy for this PR?
Covered by existing tests, with expected offsets updated to the new encoding.
`test_unique_fast_path_with_uninserted_row` (#26018) told the fast path
apart from the chain walk by their different offset encodings, which this PR
removes. This test is revised so the two paths now emit different results (the
fast path limits by probe rows, the chain walk by matches), and checked that
the test fails when the fast path is disabled. cc @jayzhan211
## Are there any user-facing changes?
No behavior change.
API change: `JoinHashMapType::get_matched_indices_with_limit_offset` and the
public `get_matched_indices_with_limit_offset` function now take and return
`ProbeOffset` instead of `(usize, Option<u64>)`.
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