[jira] [Created] (ARROW-8908) [Rust][DataFusion] improve performance of building literal arrays

["Yordan Pavlov (Jira)" <ji...@apache.org>]

Yordan Pavlov created ARROW-8908:
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             Summary: [Rust][DataFusion] improve performance of building literal arrays
                 Key: ARROW-8908
                 URL: https://issues.apache.org/jira/browse/ARROW-8908
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Rust - DataFusion
            Reporter: Yordan Pavlov


[~andygrove] I was doing some profiling and noticed a potential performance improvement described below


NOTE: The issue described below would be irrelevant if it was possible to use scalar comparison operations in DataFusion as described here:
https://issues.apache.org/jira/browse/ARROW-8907


the `build_literal_array` function defined here https://github.com/apache/arrow/blob/master/rust/datafusion/src/execution/physical_plan/expressions.rs#L1204
creates an array of literal values using a loop, but from benchmarks it appears creating an array from vec is much faster 
(about 58 times faster when building an array with 100000 values).
Here are the benchmark results:

array builder/array from vec: time: [25.644 us 25.883 us 26.214 us]
array builder/array from values: time: [1.4985 ms 1.5090 ms 1.5213 ms]

here is the benchmark code:
```
fn bench_array_builder(c: &mut Criterion) {
 let array_len = 100000;
 let mut count = 0;
 let mut group = c.benchmark_group("array builder");

group.bench_function("array from vec", |b| b.iter(|| {
 let float_array: PrimitiveArray<Float32Type> = vec![1.0; array_len].into();
 count = float_array.len();
 }));
 println!("built array with {} values", count);

group.bench_function("array from values", |b| b.iter(|| {
 // let float_array: PrimitiveArray<Float32Type> = build_literal_array(1.0, array_len);
 let mut builder = PrimitiveBuilder::<Float32Type>::new(array_len);
 for _ in 0..count {
 &builder.append_value(1.0);
 }
 let float_array = builder.finish();
 count = float_array.len();
 }));
 println!("built array with {} values", count);
}
```



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