Improve benchmark for ltrim (#12513)

* complete benchmark for ltrim.

* improve benchmarks.

* remove unused param.

* fix bench.

* refactor to remove repeated codes.

* fix clippy.

* Update datafusion/functions/benches/ltrim.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* improve codes and add more comments.

* fix clippy.

---------

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

datafusion/functions/benches/ltrim.rs

@@ -17,32 +17,221 @@
 
 extern crate criterion;
 
-use arrow::array::{ArrayRef, StringArray};
-use criterion::{black_box, criterion_group, criterion_main, Criterion};
+use arrow::array::{ArrayRef, LargeStringArray, StringArray, StringViewArray};
+use criterion::{
+    black_box, criterion_group, criterion_main, measurement::Measurement, BenchmarkGroup,
+    Criterion, SamplingMode,
+};
 use datafusion_common::ScalarValue;
-use datafusion_expr::ColumnarValue;
+use datafusion_expr::{ColumnarValue, ScalarUDF};
 use datafusion_functions::string;
-use std::sync::Arc;
+use rand::{distributions::Alphanumeric, rngs::StdRng, Rng, SeedableRng};
+use std::{fmt, sync::Arc};
 
-fn create_args(size: usize, characters: &str) -> Vec<ColumnarValue> {
-    let iter =
-        std::iter::repeat(format!("{}datafusion{}", characters, characters)).take(size);
-    let array = Arc::new(StringArray::from_iter_values(iter)) as ArrayRef;
+pub fn seedable_rng() -> StdRng {
+    StdRng::seed_from_u64(42)
+}
+
+#[derive(Clone, Copy)]
+pub enum StringArrayType {
+    Utf8View,
+    Utf8,
+    LargeUtf8,
+}
+
+impl fmt::Display for StringArrayType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            StringArrayType::Utf8View => f.write_str("string_view"),
+            StringArrayType::Utf8 => f.write_str("string"),
+            StringArrayType::LargeUtf8 => f.write_str("large_string"),
+        }
+    }
+}
+
+/// returns an array of strings, and `characters` as a ScalarValue
+pub fn create_string_array_and_characters(
+    size: usize,
+    characters: &str,
+    trimmed: &str,
+    remaining_len: usize,
+    string_array_type: StringArrayType,
+) -> (ArrayRef, ScalarValue) {
+    let rng = &mut seedable_rng();
+
+    // Create `size` rows:
+    //   - 10% rows will be `None`
+    //   - Other 90% will be strings with same `remaining_len` lengths
+    // We will build the string array on it later.
+    let string_iter = (0..size).map(|_| {
+        if rng.gen::<f32>() < 0.1 {
+            None
+        } else {
+            let mut value = trimmed.as_bytes().to_vec();
+            let generated = rng.sample_iter(&Alphanumeric).take(remaining_len);
+            value.extend(generated);
+            Some(String::from_utf8(value).unwrap())
+        }
+    });
+
+    // Build the target `string array` and `characters` according to `string_array_type`
+    match string_array_type {
+        StringArrayType::Utf8View => (
+            Arc::new(string_iter.collect::<StringViewArray>()),
+            ScalarValue::Utf8View(Some(characters.to_string())),
+        ),
+        StringArrayType::Utf8 => (
+            Arc::new(string_iter.collect::<StringArray>()),
+            ScalarValue::Utf8(Some(characters.to_string())),
+        ),
+        StringArrayType::LargeUtf8 => (
+            Arc::new(string_iter.collect::<LargeStringArray>()),
+            ScalarValue::LargeUtf8(Some(characters.to_string())),
+        ),
+    }
+}
+
+/// Create args for the ltrim benchmark
+/// Inputs:
+///   - size: rows num of the test array
+///   - characters: the characters we need to trim
+///   - trimmed: the part in the testing string that will be trimmed
+///   - remaining_len: the len of the remaining part of testing string after trimming
+///   - string_array_type: the method used to store the testing strings
+///
+/// Outputs:
+///   - testing string array
+///   - trimmed characters
+///
+fn create_args(
+    size: usize,
+    characters: &str,
+    trimmed: &str,
+    remaining_len: usize,
+    string_array_type: StringArrayType,
+) -> Vec<ColumnarValue> {
+    let (string_array, pattern) = create_string_array_and_characters(
+        size,
+        characters,
+        trimmed,
+        remaining_len,
+        string_array_type,
+    );
     vec![
-        ColumnarValue::Array(array),
-        ColumnarValue::Scalar(ScalarValue::Utf8(Some(characters.to_string()))),
+        ColumnarValue::Array(string_array),
+        ColumnarValue::Scalar(pattern),
     ]
 }
 
+#[allow(clippy::too_many_arguments)]
+fn run_with_string_type<M: Measurement>(
+    group: &mut BenchmarkGroup<'_, M>,
+    ltrim: &ScalarUDF,
+    size: usize,
+    len: usize,
+    characters: &str,
+    trimmed: &str,
+    remaining_len: usize,
+    string_type: StringArrayType,
+) {
+    let args = create_args(size, characters, trimmed, remaining_len, string_type);
+    group.bench_function(
+        format!(
+            "{string_type} [size={size}, len_before={len}, len_after={remaining_len}]",
+        ),
+        |b| b.iter(|| black_box(ltrim.invoke(&args))),
+    );
+}
+
+#[allow(clippy::too_many_arguments)]
+fn run_one_group(
+    c: &mut Criterion,
+    group_name: &str,
+    ltrim: &ScalarUDF,
+    string_types: &[StringArrayType],
+    size: usize,
+    len: usize,
+    characters: &str,
+    trimmed: &str,
+    remaining_len: usize,
+) {
+    let mut group = c.benchmark_group(group_name);
+    group.sampling_mode(SamplingMode::Flat);
+    group.sample_size(10);
+
+    for string_type in string_types {
+        run_with_string_type(
+            &mut group,
+            ltrim,
+            size,
+            len,
+            characters,
+            trimmed,
+            remaining_len,
+            *string_type,
+        );
+    }
+
+    group.finish();
+}
+
 fn criterion_benchmark(c: &mut Criterion) {
     let ltrim = string::ltrim();
-    for char in ["\"", "Header:"] {
-        for size in [1024, 4096, 8192] {
-            let args = create_args(size, char);
-            c.bench_function(&format!("ltrim {}: {}", char, size), |b| {
-                b.iter(|| black_box(ltrim.invoke(&args)))
-            });
-        }
+    let characters = ",!()";
+
+    let string_types = [
+        StringArrayType::Utf8View,
+        StringArrayType::Utf8,
+        StringArrayType::LargeUtf8,
+    ];
+    for size in [1024, 4096, 8192] {
+        // len=12, trimmed_len=4, len_after_ltrim=8
+        let len = 12;
+        let trimmed = characters;
+        let remaining_len = len - trimmed.len();
+        run_one_group(
+            c,
+            "INPUT LEN <= 12",
+            &ltrim,
+            &string_types,
+            size,
+            len,
+            characters,
+            trimmed,
+            remaining_len,
+        );
+
+        // len=64, trimmed_len=4, len_after_ltrim=60
+        let len = 64;
+        let trimmed = characters;
+        let remaining_len = len - trimmed.len();
+        run_one_group(
+            c,
+            "INPUT LEN > 12, OUTPUT LEN > 12",
+            &ltrim,
+            &string_types,
+            size,
+            len,
+            characters,
+            trimmed,
+            remaining_len,
+        );
+
+        // len=64, trimmed_len=56, len_after_ltrim=8
+        let len = 64;
+        let trimmed = characters.repeat(15);
+        let remaining_len = len - trimmed.len();
+        run_one_group(
+            c,
+            "INPUT LEN > 12, OUTPUT LEN <= 12",
+            &ltrim,
+            &string_types,
+            size,
+            len,
+            characters,
+            &trimmed,
+            remaining_len,
+        );
     }
 }