xudong963 opened a new pull request, #15761:
URL: https://github.com/apache/datafusion/pull/15761
## Which issue does this PR close?
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- Closes #.
## Rationale for this change
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In our prod, we found that the `optimize_projection` is slow when the number
of columns is large, and `is_projection_unnecessary` is a bottleneck. After
checking the method, I found we can improve it.
Here is the benchmark:
### Result
v1 is the old and v2 is the optimized version
```
Projection Optimization/v1_one_non_trivial
time: [92.212 µs 93.578 µs 95.428 µs]
Found 16 outliers among 100 measurements (16.00%)
2 (2.00%) high mild
14 (14.00%) high severe
Projection Optimization/v2_one_non_trivial
time: [242.52 ns 248.62 ns 256.51 ns]
Found 9 outliers among 100 measurements (9.00%)
4 (4.00%) high mild
5 (5.00%) high severe
```
### Benchmark code
1000 exprs in Projection, and one of them is non-trival expr.
```rust
use arrow::datatypes::{DataType, Field, Schema};
use criterion::{criterion_group, criterion_main, Criterion};
use datafusion_expr::{binary_expr, col,Operator, Expr, LogicalPlan,
table_scan};
use datafusion_optimizer::optimize_projections::{is_projection_unnecessary,
is_projection_unnecessary_v2};
pub fn test_table_scan_fields() -> Vec<Field> {
vec![
Field::new("a", DataType::UInt32, false),
Field::new("b", DataType::UInt32, false),
Field::new("c", DataType::UInt32, false),
]
}
pub fn test_table_scan_with_name(name: &str) ->
datafusion_common::Result<LogicalPlan> {
let schema = Schema::new(test_table_scan_fields());
table_scan(Some(name), &schema, None)?.build()
}
/// some tests share a common table
pub fn test_table_scan() -> datafusion_common::Result<LogicalPlan> {
test_table_scan_with_name("test")
}
fn create_mixed_expressions(count: usize) -> Vec<Expr> {
let mut exprs = Vec::with_capacity(count);
for i in 0..count {
// Most expressions are just column references
if i != count / 2 {
match i % 3 {
0 => exprs.push(col("a")),
1 => exprs.push(col("b")),
_ => exprs.push(col("c")),
}
} else {
// One non-trivial expression (binary operation)
exprs.push(binary_expr(col("a"), Operator::Plus, col("b")));
}
}
exprs
}
fn benchmark_projections(c: &mut Criterion) {
let input_plan = test_table_scan().unwrap();
let one_non_trivial = create_mixed_expressions(1000);
let mut group = c.benchmark_group("Projection Optimization");
// Benchmark with one non-trivial expression
group.bench_function("v1_one_non_trivial", |b| {
b.iter(|| is_projection_unnecessary(&input_plan, &one_non_trivial));
});
group.bench_function("v2_one_non_trivial", |b| {
b.iter(|| is_projection_unnecessary_v2(&input_plan,
&one_non_trivial));
});
group.finish();
}
criterion_group!(benches, benchmark_projections);
criterion_main!(benches);
```
## What changes are included in this PR?
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## Are these changes tested?
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Yes
## Are there any user-facing changes?
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