perf: compute cardinality from list/map offsets - #25079
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`cardinality` was implemented by iterating over the `values` of the input `GenericListArray`, creating a slice for each logical row, and then fetching the length of the slice. This incurs a lot of unnecessary per-row overhead; we can instead determine the cardinality of each list by looking at the `OffsetBuffer`. For non-nested lists, this is straightforward. It would be possible to use a similar approach to compute the cardinality of nested lists, but for now this PR falls back to the previous approach for that case. Add a benchmark, plus tests for lists (sliced, unsliced, LargeList) and maps, including nulls and empty batches. Benchmarks: (M4 Max) list/valid/8192x32, 203.951 µs → 0.984 µs, -99.52% large_list/nullable/8192x32, 172.699 µs → 1.049 µs, -99.39% map/valid/8192x32, 471.074 µs → 0.958 µs, -99.80%
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## main #25079 +/- ##
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- Coverage 81.74% 81.74% -0.01%
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Files 1128 1128
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Branches 416644 416698 +54
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Which issue does this PR close?
cardinalityfrom offsets #25078Rationale for this change
cardinalitywas implemented by iterating over thevaluesof the inputGenericListArray, creating a slice for each logical row, and then fetching the length of the slice. This incurs a lot of unnecessary per-row overhead; we can instead determine the cardinality of each list by looking at theOffsetBuffer. This is roughly 100x-500x faster.For non-nested lists, this is straightforward. It would be possible to use a similar approach to compute the cardinality of nested lists, but for now this PR falls back to the previous approach for that case.
Benchmarks: (M4 Max)
list/valid/8192x32, 203.951 µs → 0.984 µs, -99.52%
large_list/nullable/8192x32, 172.699 µs → 1.049 µs, -99.39%
map/valid/8192x32, 471.074 µs → 0.958 µs, -99.80%
What changes are included in this PR?
cardinalityfor non-nested lists/mapsWhat is the testing strategy for this PR?
Existing tests pass; new tests added.
Are there any user-facing changes?
No.