fix(compute/exec): do not carry a cached null count across ArraySpan.SetSlice - #1306
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fix(compute/exec): do not carry a cached null count across ArraySpan.SetSlice#1306singhpratech wants to merge 1 commit into
singhpratech wants to merge 1 commit into
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…SetSlice SetSlice kept the cached null count for the new slice when it was 0 or equal to the old length. That is only right while the count describes the whole span; a kernel that calls UpdateNullCount on the span the executor reuses stores the slice's count, and the next SetSlice then treats the following slice as all valid or all null. and_kleene and or_kleene return false where the answer is null once ExecCtx.ChunkSize is below the input length. Reset the count to unknown whenever a validity bitmap is present, as the C++ ArraySpan::SetSlice does, and add the chunk-size test.
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Rationale for this change
and_kleeneandor_kleenereturnfalsewhere the answer is null whenExecCtx.ChunkSizeisbelow the input length (#1305).
ArraySpan.SetSlicekept the cached null count for the newslice when it was
0or equal to the old length. That is only right while the count describes thewhole span. The executor reuses one span per argument across slices, and a kernel that calls
UpdateNullCount()on it stores the slice's count, so the nextSetSlicetreats the followingslice as all valid or all null.
What changes are included in this PR?
SetSliceresets the count toUnknownNullCountwhenever a validity bitmap is present, as the C++ArraySpan::SetSlicedoes (cpp/src/arrow/array/data.h), and keeps it unknown when it was alreadynon-zero without a bitmap. The null type still gets the slice length; a span with no bitmap and a
zero count keeps zero. Two cases added to
TestArraySpan_SetSlice, and a new test that runs bothKleene kernels at chunk sizes 1, 2, 3, 4 and 8 against the default result.
Cost: a slice of an all-valid array with a bitmap now reports an unknown count, so a kernel that
asks pays one popcount over the slice instead of reading the cache. That is the C++ behaviour.
Are these changes tested?
Yes. The new chunk-size test fails on main (four assertions, chunk sizes 1 and 2 for both kernels)
and passes with the change;
go test ./arrow/compute/...passes.Are there any user-facing changes?
Results of
and_kleene/or_kleeneno longer depend onExecCtx.ChunkSize.ArraySpan.NullsafterSetSliceisUnknownNullCountin cases where it was previously0or the slice length; code thatread it directly should call
UpdateNullCount(), which is what the package's own kernels do.Closes #1305.