Fokko commented on code in PR #9426:
URL: https://github.com/apache/arrow-rs/pull/9426#discussion_r2832742355
##########
arrow-array/src/builder/generic_bytes_builder.rs:
##########
@@ -110,6 +110,19 @@ impl<T: ByteArrayType> GenericByteBuilder<T> {
self.offsets_builder.push(self.next_offset());
}
+ /// Appends a value of type `T` into the builder `n` times.
+ ///
+ /// See [`Self::append_value`] for more panic information.
+ #[inline]
+ pub fn append_value_n(&mut self, value: impl AsRef<T::Native>, n: usize) {
+ let bytes = value.as_ref().as_ref();
+ for _ in 0..n {
+ self.value_builder.extend_from_slice(bytes);
Review Comment:
My friend Claude created a benchmark:
```rust
// 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::builder::StringBuilder;
use criterion::*;
use std::hint;
fn bench_append_value(c: &mut Criterion) {
let mut group = c.benchmark_group("append_value");
for &str_len in &[5, 30, 1024] {
let value = "x".repeat(str_len);
for &n in &[100, 1000, 10000, 100000] {
group.throughput(Throughput::Elements(n as u64));
group.bench_with_input(
BenchmarkId::new(format!("n={n}"), format!("len={str_len}")),
&(&value, n),
|b, &(value, n)| {
b.iter(|| {
let mut builder = StringBuilder::new();
for _ in 0..n {
builder.append_value(value);
}
hint::black_box(builder.finish());
})
},
);
}
}
group.finish();
}
fn bench_append_value_n(c: &mut Criterion) {
let mut group = c.benchmark_group("append_value_n");
for &str_len in &[5, 30, 1024] {
let value = "x".repeat(str_len);
for &n in &[100, 1000, 10000, 100000] {
group.throughput(Throughput::Elements(n as u64));
group.bench_with_input(
BenchmarkId::new(format!("n={n}"), format!("len={str_len}")),
&(&value, n),
|b, &(value, n)| {
b.iter(|| {
let mut builder = StringBuilder::new();
builder.append_value_n(value, n);
hint::black_box(builder.finish());
})
},
);
}
}
group.finish();
}
criterion_group!(benches, bench_append_value, bench_append_value_n);
criterion_main!(benches);
```
Let me know if you find this valuable to add to the repository.
This resulted in:
```
append_value_n improvements with reserve():
┌────────────────────┬─────────┬─────────┬─────────────┐
│ Config │ Before │ After │ Improvement │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=1000, len=5 │ 2.96 µs │ 2.68 µs │ ~9% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=10000, len=5 │ 29.3 µs │ 26.4 µs │ ~10% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=100000, len=5 │ 268 µs │ 249 µs │ ~7% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=100, len=30 │ 628 ns │ 548 ns │ ~13% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=1000, len=30 │ 4.22 µs │ 3.68 µs │ ~13% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=10000, len=30 │ 43.9 µs │ 36.3 µs │ ~17% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=100000, len=30 │ 404 µs │ 350 µs │ ~13% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=100, len=1024 │ 3.16 µs │ 1.93 µs │ ~39% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=1000, len=1024 │ 13.7 µs │ 11.1 µs │ ~19% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=10000, len=1024 │ 729 µs │ 103 µs │ ~86% │
├────────────────────┼─────────┼─────────┼─────────────┤
│ n=100000, len=1024 │ 8.68 ms │ 1.02 ms │ ~88% │
└────────────────────┴─────────┴─────────┴─────────────┘
```
Keep in mind that the benchmark uses `::new` rather than `::with_capacity`.
We can see that `.reserve` offers some benefits if you don't pre-allocate.
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