Improve lpad udf by using a GenericStringBuilder (#11987)

* Update LPAD scalar function to support Utf8View

* Lpad code improvements and benchmark.

* Improved use of GenericStringBuilder.

datafusion/functions/Cargo.toml

@@ -146,3 +146,8 @@ required-features = ["string_expressions"]
 harness = false
 name = "upper"
 required-features = ["string_expressions"]
+
+[[bench]]
+harness = false
+name = "pad"
+required-features = ["unicode_expressions"]

datafusion/functions/benches/pad.rs

@@ -0,0 +1,141 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use arrow::array::{ArrayRef, ArrowPrimitiveType, OffsetSizeTrait, PrimitiveArray};
+use arrow::datatypes::Int64Type;
+use arrow::util::bench_util::{
+    create_string_array_with_len, create_string_view_array_with_len,
+};
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion};
+use datafusion_expr::ColumnarValue;
+use datafusion_functions::unicode::{lpad, rpad};
+use rand::distributions::{Distribution, Uniform};
+use rand::Rng;
+use std::sync::Arc;
+
+struct Filter<Dist> {
+    dist: Dist,
+}
+
+impl<T, Dist> Distribution<T> for Filter<Dist>
+where
+    Dist: Distribution<T>,
+{
+    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> T {
+        self.dist.sample(rng)
+    }
+}
+
+pub fn create_primitive_array<T>(
+    size: usize,
+    null_density: f32,
+    len: usize,
+) -> PrimitiveArray<T>
+where
+    T: ArrowPrimitiveType<Native = i64>,
+{
+    let dist = Filter {
+        dist: Uniform::new_inclusive::<i64, i64>(0, len as i64),
+    };
+
+    let mut rng = rand::thread_rng();
+    (0..size)
+        .map(|_| {
+            if rng.gen::<f32>() < null_density {
+                None
+            } else {
+                Some(rng.sample(&dist))
+            }
+        })
+        .collect()
+}
+
+fn create_args<O: OffsetSizeTrait>(
+    size: usize,
+    str_len: usize,
+    use_string_view: bool,
+) -> Vec<ColumnarValue> {
+    let length_array = Arc::new(create_primitive_array::<Int64Type>(size, 0.0, str_len));
+
+    if !use_string_view {
+        let string_array =
+            Arc::new(create_string_array_with_len::<O>(size, 0.1, str_len));
+        let fill_array = Arc::new(create_string_array_with_len::<O>(size, 0.1, str_len));
+
+        vec![
+            ColumnarValue::Array(string_array),
+            ColumnarValue::Array(Arc::clone(&length_array) as ArrayRef),
+            ColumnarValue::Array(fill_array),
+        ]
+    } else {
+        let string_array =
+            Arc::new(create_string_view_array_with_len(size, 0.1, str_len, false));
+        let fill_array =
+            Arc::new(create_string_view_array_with_len(size, 0.1, str_len, false));
+
+        vec![
+            ColumnarValue::Array(string_array),
+            ColumnarValue::Array(Arc::clone(&length_array) as ArrayRef),
+            ColumnarValue::Array(fill_array),
+        ]
+    }
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    for size in [1024, 2048] {
+        let mut group = c.benchmark_group("lpad function");
+
+        let args = create_args::<i32>(size, 32, false);
+        group.bench_function(BenchmarkId::new("utf8 type", size), |b| {
+            b.iter(|| criterion::black_box(lpad().invoke(&args).unwrap()))
+        });
+
+        let args = create_args::<i64>(size, 32, false);
+        group.bench_function(BenchmarkId::new("largeutf8 type", size), |b| {
+            b.iter(|| criterion::black_box(lpad().invoke(&args).unwrap()))
+        });
+
+        let args = create_args::<i32>(size, 32, true);
+        group.bench_function(BenchmarkId::new("stringview type", size), |b| {
+            b.iter(|| criterion::black_box(lpad().invoke(&args).unwrap()))
+        });
+
+        group.finish();
+
+        let mut group = c.benchmark_group("rpad function");
+
+        let args = create_args::<i32>(size, 32, false);
+        group.bench_function(BenchmarkId::new("utf8 type", size), |b| {
+            b.iter(|| criterion::black_box(rpad().invoke(&args).unwrap()))
+        });
+
+        let args = create_args::<i64>(size, 32, false);
+        group.bench_function(BenchmarkId::new("largeutf8 type", size), |b| {
+            b.iter(|| criterion::black_box(rpad().invoke(&args).unwrap()))
+        });
+        //
+        // let args = create_args::<i32>(size, 32, true);
+        // group.bench_function(BenchmarkId::new("stringview type", size), |b| {
+        //     b.iter(|| criterion::black_box(rpad().invoke(&args).unwrap()))
+        // });
+
+        group.finish();
+    }
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);