CuteChuanChuan commented on code in PR #19994:
URL: https://github.com/apache/datafusion/pull/19994#discussion_r2746696533
##########
datafusion/physical-expr/benches/case_when.rs:
##########
@@ -517,5 +519,106 @@ fn benchmark_lookup_table_case_when(c: &mut Criterion,
batch_size: usize) {
}
}
+fn benchmark_divide_by_zero_protection(c: &mut Criterion, batch_size: usize) {
+ let mut group = c.benchmark_group("divide_by_zero_protection");
+
+ for zero_percentage in [0.0, 0.1, 0.5, 0.9] {
+ let rng = &mut seedable_rng();
+
+ let numerator: Int32Array =
+ (0..batch_size).map(|_| Some(rng.random::<i32>())).collect();
+
+ let divisor_values: Vec<Option<i32>> = (0..batch_size)
+ .map(|_| {
+ let roll: f32 = rng.random();
+ if roll < zero_percentage {
+ Some(0)
+ } else {
+ let mut val = rng.random::<i32>();
+ while val == 0 {
+ val = rng.random::<i32>();
+ }
+ Some(val)
+ }
+ })
+ .collect();
+
+ let divisor: Int32Array = divisor_values.iter().cloned().collect();
+ let divisor_copy: Int32Array =
divisor_values.iter().cloned().collect();
+
+ let schema = Arc::new(Schema::new(vec![
+ Field::new("numerator", numerator.data_type().clone(), true),
+ Field::new("divisor", divisor.data_type().clone(), true),
+ Field::new("divisor_copy", divisor_copy.data_type().clone(), true),
+ ]));
+
+ let batch = RecordBatch::try_new(
+ Arc::clone(&schema),
+ vec![
+ Arc::new(numerator),
+ Arc::new(divisor),
+ Arc::new(divisor_copy),
+ ],
+ )
+ .unwrap();
+
+ let numerator_col = col("numerator", &batch.schema()).unwrap();
+ let divisor_col = col("divisor", &batch.schema()).unwrap();
+ let divisor_copy_col = col("divisor_copy", &batch.schema()).unwrap();
+
+ group.bench_function(
+ format!(
+ "{} rows, {}% zeros: DivideByZeroProtection",
+ batch_size,
+ (zero_percentage * 100.0) as i32
+ ),
+ |b| {
+ let when = Arc::new(BinaryExpr::new(
+ Arc::clone(&divisor_col),
+ Operator::Gt,
+ lit(0i32),
+ ));
+ let then = Arc::new(BinaryExpr::new(
+ Arc::clone(&numerator_col),
+ Operator::Divide,
+ Arc::clone(&divisor_col),
+ ));
+ let else_null: Arc<dyn PhysicalExpr> =
lit(ScalarValue::Int32(None));
+ let expr =
+ Arc::new(case(None, vec![(when, then)],
Some(else_null)).unwrap());
+
+ b.iter(|| black_box(expr.evaluate(black_box(&batch)).unwrap()))
+ },
+ );
+
+ group.bench_function(
Review Comment:
Hi @pepijnve ,
The key difference is in which column is used in the **WHEN** condition:
- First benchmark (`DivideByZeroProtection`): checks **divisor_col** > 0,
and since divisor_col is also the divisor in numerator / divisor_col, this
matches the pattern and triggers the optimization.
- Second benchmark (`ExpressionOrExpression`): checks **divisor_copy_col** >
0, but the division uses divisor_col. Since the checked column doesn't match
the divisor, the optimization is not triggered and it falls back to
ExpressionOrExpression.
I'll also add a comment in the code to make this distinction clearer.
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