zanmato1984 commented on code in PR #42106:
URL: https://github.com/apache/arrow/pull/42106#discussion_r1635806122
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cpp/src/arrow/compute/expression.cc:
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@@ -732,6 +776,10 @@ Result<Datum> ExecuteScalarExpression(const Expression&
expr, const ExecBatch& i
"ExecuteScalarExpression cannot Execute non-scalar expression ",
expr.ToString());
}
+ if (!expr.selection_vector_aware() && input.selection_vector) {
Review Comment:
This actually implies a strategy (1) that is: if any subexpression
(including the top-level expression itself) is not selection vector aware, we
do the gather/scatter work only once for the top-level expression. This way all
the subexpressions can work on a (gathered) continuous input.
An alternative strategy (2) could be: every expression that is not selection
vector aware (not counting its subexpressions), does the gather/scatter itself.
This way every expression itself maintains the input/output shape same as the
original input batch.
Given that for a long time (possibly forever), there will be much less
selection vector aware kernels than the other, it's probably worth it to use 1
instead of 2, as the gather/scatter only happen once for the whole expression.
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