[compiler] fix TableUnion lowering #13414
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TableUnion was always collapsing to a single partition when the key was empty. This adds a special case handling, which just concatenates partitions. The body of the resulting TableStage is a little hacky: it does a StreamMultiMerge, but where exactly one input stream is non-empty. I think that should have fine performance, and I didn’t see any simpler ways to do it.
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bump @chrisvittal |
danking
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Aug 15, 2023
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Other than my comment, I think I understand this enough to feel confident approving.
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fixes #13407
CHANGELOG: Resolves #13407 in which uses of
union_rowscould reduce parallelism to one partition resulting in severely degraded performance.TableUnion was always collapsing to a single partition when the key was empty. This adds a special case handling, which just concatenates partitions.
The body of the resulting TableStage is a little hacky: it does a StreamMultiMerge, but where exactly one input stream is non-empty. I think that should have fine performance, and I didn’t see any simpler ways to do it.