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fix: drain PiecewiseMergeJoin output before state transitions - #24298
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## main #24298 +/- ##
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comphead
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Aug 14, 2026
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Thanks @buraksenn looks solid for me. I was thinking to move test to slt, but current implementation is good
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Thank you @buraksenn and @comphead |
imtherealnaska
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…#24298) ## Which issue does this PR close? - Closes apache#24297 ## Rationale for this change `ClassicPWMJStream` transitions phases while its output `BatchCoalescer` still holds completed batches. The Left/Full unmatched pass falls back into its producer when the drained queue is an exact multiple of `batch_size` — emitting duplicate rows forever — and queued unmatched Right/Full batches are dropped at terminal transitions. A zero-row placeholder batch also escapes as stream output on empty results. ## What changes are included in this PR? - Add `BatchProcessState::next_drained_batch()` (`finish_buffered_batch` + `next_completed_batch`); `None` guarantees the coalescer is empty - `process_stream_batch` and `process_unmatched_buffered_batch` drain one batch per poll and transition only after a confirmed-empty pop, so a finished producer can never re-run and no queued batch is lost - Scan completion returns `StatefulStreamResult::Continue` instead of the empty placeholder batch; empty joins now yield no batches ## Are these changes tested? Yes. The existing unmatched Left/Right tests now run with `batch_size = 1` (the Left one bounded with `take(6)` so the old duplicate loop fails as a snapshot mismatch instead of hanging) — both fail on main and pass here. The empty-join tests assert no batches are emitted. ## Are there any user-facing changes? No (PWMJ is experimental and off by default).
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Which issue does this PR close?
PiecewiseMergeJoinchanges state before draining its output coalescer: the Left/Full unmatched pass repeats forever, queued Right/Full rows can be dropped #24297Rationale for this change
ClassicPWMJStreamtransitions phases while its outputBatchCoalescerstill holds completed batches. The Left/Full unmatched pass falls back into its producer when the drained queue is an exact multiple ofbatch_size— emitting duplicate rows forever — and queued unmatched Right/Full batches are dropped at terminal transitions. A zero-row placeholder batch also escapes as stream output on empty results.What changes are included in this PR?
BatchProcessState::next_drained_batch()(finish_buffered_batch+next_completed_batch);Noneguarantees the coalescer is emptyprocess_stream_batchandprocess_unmatched_buffered_batchdrain one batch per poll and transition only after a confirmed-empty pop, so a finished producer can never re-run and no queued batch is lostStatefulStreamResult::Continueinstead of the empty placeholder batch; empty joins now yield no batchesAre these changes tested?
Yes. The existing unmatched Left/Right tests now run with
batch_size = 1(the Left one bounded withtake(6)so the old duplicate loop fails as a snapshot mismatch instead of hanging) — both fail on main and pass here. The empty-join tests assert no batches are emitted.Are there any user-facing changes?
No (PWMJ is experimental and off by default).