xudong963 opened a new pull request, #15746:
URL: https://github.com/apache/datafusion/pull/15746
## Which issue does this PR close?
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- Closes #.
## Rationale for this change
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the issue then this section is not needed.
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If the two projections have same exprs (my real case). We can directly
remove the current projection and return the child projection. Avoid really
running the `merge_consecutive_projections` method. This would improve
performance if the projections have many exprs
### Benchmark
```rust
use criterion::{criterion_group, criterion_main, Criterion};
use datafusion_common::{DFSchema, ScalarValue, Result};
use datafusion_expr::{col, lit, Expr, LogicalPlan, Projection};
use std::sync::Arc;
use
datafusion_optimizer::optimize_projections::{merge_consecutive_projections,
merge_consecutive_projections_v2};
/// Creates a projection with another projection as input, both with n
expressions
fn create_nested_projection(n_exprs: usize) -> Result<Projection> {
// Create a simple empty relation as the base
let schema = Arc::new(DFSchema::empty());
let base_plan = LogicalPlan::EmptyRelation(
datafusion_expr::EmptyRelation {
produce_one_row: true,
schema: schema.clone(),
}
);
// Create inner projection with n expressions (i AS col_i)
let inner_exprs: Vec<Expr> = (0..n_exprs)
.map(|i| lit(ScalarValue::Int32(Some(i as
i32))).alias(format!("col_{}", i)))
.collect();
let inner_projection = Projection::try_new(
inner_exprs.clone(),
Arc::new(base_plan)
)?;
Projection::try_new(
inner_exprs,
Arc::new(LogicalPlan::Projection(inner_projection))
)
}
fn bench_merge_consecutive_projections(c: &mut Criterion) {
let n_exprs = 1000;
let projection = create_nested_projection(n_exprs).unwrap();
let mut group = c.benchmark_group("projection_merge");
group.bench_function("merge_consecutive_projections", |b| {
b.iter(|| {
let proj_clone = projection.clone();
merge_consecutive_projections(proj_clone).unwrap()
});
});
group.bench_function("merge_consecutive_projections_v2", |b| {
b.iter(|| {
let proj_clone = projection.clone();
merge_consecutive_projections_v2(proj_clone).unwrap()
});
});
group.finish();
}
criterion_group!(benches, bench_merge_consecutive_projections);
criterion_main!(benches);
```
### Benchmark result
```
Finished `bench` profile [optimized] target(s) in 36.80s
Running benches/projection_merge.rs
(arrow-datafusion/target/release/deps/projection_merge-968d896acadbdb0b)
projection_merge/merge_consecutive_projections
time: [219.66 µs 220.36 µs 221.21 µs]
Found 4 outliers among 100 measurements (4.00%)
3 (3.00%) high mild
1 (1.00%) high severe
projection_merge/merge_consecutive_projections_v2
time: [66.409 µs 66.974 µs 67.756 µs]
Found 5 outliers among 100 measurements (5.00%)
1 (1.00%) high mild
4 (4.00%) high severe
```
## What changes are included in this PR?
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sometimes worth providing a summary of the individual changes in this PR.
-->
Add a fast path
## Are these changes tested?
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By existing tests
## Are there any user-facing changes?
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