kongfanshen-0801 opened a new pull request, #1799:
URL: https://github.com/apache/cloudberry/pull/1799
## What
Backports two upstream PostgreSQL commits that add **Hash Right Semi Join**:
- `aa86129e1` — Support "Right Semi Join" plan shapes
- `5668a857d` — Fix right-semi-joins in HashJoin rescans
This lets the planner build the hash table on the smaller (LHS) side of an
`IN`/`EXISTS` semijoin instead of always hashing the inner relation.
## Cloudberry/GPDB-specific adaptations
- **nodes.h**: `JOIN_RIGHT_SEMI` is appended at the **end** of the `JoinType`
enum rather than in upstream's mid-list position. Inserting it mid-list
shifts the integer values of the GPDB-only `JOIN_DEDUP_SEMI`/`_REVERSE` and
`JOIN_UNIQUE_*` codes, which corrupts MPP motion planning and crashes
during
dispatch (SIGSEGV in `setupCdbProcessList`). Appending keeps every existing
value stable.
- **cdbpath.c** (`cdbpath_motion_for_join`, serial + parallel switches):
handle `JOIN_RIGHT_SEMI` like `JOIN_RIGHT`/`JOIN_RIGHT_ANTI` — the inner
(build) side must not be replicated, since a right-semi join emits
build-side rows.
- **joinrels.c**: add the `JOIN_RIGHT_SEMI` path alongside `JOIN_SEMI` while
preserving the existing GPDB `JOIN_DEDUP_SEMI` handling.
## Testing
- Functional: `Hash Right Semi Join` is chosen for small-build-side
semijoins;
results verified correct (dedup semantics, rescan correctness, MPP
execution
across segments).
- Regression: the `join` test expected output is still being reconciled
against CI's canonical environment — hence this PR is opened as a
**draft**.
## Notes
- Only affects the PostgreSQL planner (`optimizer=off`); GPORCA does not
generate `JOIN_RIGHT_SEMI`.
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