martin-g commented on code in PR #20114: URL: https://github.com/apache/datafusion/pull/20114#discussion_r2759037509
########## datafusion/functions/benches/left_right.rs: ########## @@ -0,0 +1,166 @@ +// 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. + +extern crate criterion; + +use std::hint::black_box; +use std::sync::Arc; + +use arrow::array::{ArrayRef, Int64Array}; +use arrow::datatypes::{DataType, Field}; +use arrow::util::bench_util::{ + create_string_array_with_len, create_string_view_array_with_len, +}; +use criterion::{BenchmarkId, Criterion, criterion_group, criterion_main}; +use datafusion_common::config::ConfigOptions; +use datafusion_expr::{ColumnarValue, ScalarFunctionArgs}; +use datafusion_functions::unicode::{left, right}; + +fn create_args( + size: usize, + str_len: usize, + use_negative: bool, + is_string_view: bool, +) -> Vec<ColumnarValue> { + let string_arg = if is_string_view { + ColumnarValue::Array(Arc::new(create_string_view_array_with_len( + size, 0.1, str_len, true, + ))) + } else { + ColumnarValue::Array(Arc::new(create_string_array_with_len::<i32>( + size, 0.1, str_len, + ))) + }; + + // For negative n, we want to trigger the double-iteration code path + let n_values: Vec<i64> = if use_negative { + (0..size).map(|i| -((i % 10 + 1) as i64)).collect() + } else { + (0..size).map(|i| (i % 10 + 1) as i64).collect() + }; + let n_array = Arc::new(Int64Array::from(n_values)); + + vec![ + string_arg, + ColumnarValue::Array(Arc::clone(&n_array) as ArrayRef), + ] +} + +fn criterion_benchmark(c: &mut Criterion) { + let left_function = left(); + let right_function = right(); + + for function in [left_function, right_function] { + for is_string_view in [false, true] { + for size in [1024, 4096] { + let function_name = function.name(); + let mut group = c.benchmark_group(format!("{function_name} size={size}")); + + // Benchmark with positive n (no optimization needed) + let mut bench_name = if is_string_view { + "string_view_array positive n" + } else { + "string_array positive n" + }; + let return_type = if is_string_view { + DataType::Utf8View + } else { + DataType::Utf8 + }; + + let args = create_args(size, 32, false, is_string_view); + group.bench_function(BenchmarkId::new(bench_name, size), |b| { + let arg_fields = args + .iter() + .enumerate() + .map(|(idx, arg)| { + Field::new(format!("arg_{idx}"), arg.data_type(), true).into() + }) + .collect::<Vec<_>>(); + let config_options = Arc::new(ConfigOptions::default()); + + b.iter(|| { + black_box( + function + .invoke_with_args(ScalarFunctionArgs { + args: args.clone(), + arg_fields: arg_fields.clone(), + number_rows: size, + return_field: Field::new( + "f", + return_type.clone(), + true, + ) + .into(), + config_options: Arc::clone(&config_options), + }) + .expect("should work"), + ) + }) + }); + + // Benchmark with negative n (triggers optimization) Review Comment: The code below is very similar to the "positive" logic above. Would it be a good idea to add `for is_negative in [false, true] {` before/after `for is_string_view in [false, true]` and merge them ? ########## datafusion/functions/src/unicode/common.rs: ########## @@ -0,0 +1,188 @@ +// 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. + +//! Common utilities for implementing unicode functions + +use arrow::array::{ + Array, ArrayAccessor, ArrayIter, ArrayRef, ByteView, GenericStringArray, Int64Array, + OffsetSizeTrait, StringViewArray, make_view, +}; +use arrow::datatypes::DataType; +use arrow_buffer::{NullBuffer, ScalarBuffer}; +use datafusion_common::cast::{ + as_generic_string_array, as_int64_array, as_string_view_array, +}; +use datafusion_common::exec_err; +use std::cmp::Ordering; +use std::ops::Range; +use std::sync::Arc; + +/// A trait for `left` and `right` byte slicing operations +pub(crate) trait LeftRightSlicer { + fn slice(string: &str, n: i64) -> Range<usize>; +} + +pub(crate) struct LeftSlicer {} + +impl LeftRightSlicer for LeftSlicer { + fn slice(string: &str, n: i64) -> Range<usize> { + if n == 0 { + // Return nothing for `n=0` + 0..0 + } else { + 0..left_right_byte_length(string, n) + } + } +} + +pub(crate) struct RightSlicer {} + +impl LeftRightSlicer for RightSlicer { + fn slice(string: &str, n: i64) -> Range<usize> { + if n == 0 { + // Return nothing for `n=0` + 0..0 + } else if n == i64::MIN { + // Special case for i64::MIN overflow + 0..0 + } else { + left_right_byte_length(string, -n)..string.len() + } + } +} + +/// Calculate the byte length of the substring of `n` chars from string `string` +#[inline] +fn left_right_byte_length(string: &str, n: i64) -> usize { + match n.cmp(&0) { + Ordering::Less => string + .char_indices() + .nth_back((n.unsigned_abs().min(usize::MAX as u64) - 1) as usize) + .map(|(index, _)| index) + .unwrap_or(0), + Ordering::Equal => 0, + Ordering::Greater => string + .char_indices() + .nth(n.unsigned_abs().min(usize::MAX as u64) as usize) + .map(|(index, _)| index) + .unwrap_or(string.len()), + } +} + +/// General implementation for `left` and `right` functions +pub(crate) fn general_left_right<F: LeftRightSlicer>( + args: &[ArrayRef], +) -> datafusion_common::Result<ArrayRef> { + let n_array = as_int64_array(&args[1])?; + + match args[0].data_type() { + DataType::Utf8 => { + let string_array = as_generic_string_array::<i32>(&args[0])?; + general_left_right_array::<i32, _, F>(string_array, n_array) + } + DataType::LargeUtf8 => { + let string_array = as_generic_string_array::<i64>(&args[0])?; + general_left_right_array::<i64, _, F>(string_array, n_array) + } + DataType::Utf8View => { + let string_view_array = as_string_view_array(&args[0])?; + general_left_right_view::<F>(string_view_array, n_array) + } + _ => exec_err!("Not supported"), + } +} + +/// `general_left_right` implementation for strings +fn general_left_right_array< + 'a, + T: OffsetSizeTrait, + V: ArrayAccessor<Item = &'a str>, + F: LeftRightSlicer, +>( + string_array: V, + n_array: &Int64Array, +) -> datafusion_common::Result<ArrayRef> { + let iter = ArrayIter::new(string_array); + let result = iter + .zip(n_array.iter()) + .map(|(string, n)| match (string, n) { + (Some(string), Some(n)) => { + let range = F::slice(string, n); + // Extract a given range from a byte-indexed slice + Some(&string[range]) + } + _ => None, + }) + .collect::<GenericStringArray<T>>(); + + Ok(Arc::new(result) as ArrayRef) +} + +/// `general_left_right` implementation for StringViewArray +fn general_left_right_view<F: LeftRightSlicer>( + string_view_array: &StringViewArray, + n_array: &Int64Array, +) -> datafusion_common::Result<ArrayRef> { + let len = n_array.len(); + + let views = string_view_array.views(); + // Every string in StringViewArray has one corresponding view in `views` + debug_assert!(views.len() == string_view_array.len()); + + // Compose null buffer at once + let string_nulls = string_view_array.nulls(); + let n_nulls = n_array.nulls(); + let new_nulls = NullBuffer::union(string_nulls, n_nulls); + + let new_views = (0..len) + .map(|idx| { + let view = views[idx]; + + let is_valid = match &new_nulls { + Some(nulls_buf) => nulls_buf.is_valid(idx), + None => true, + }; + + if is_valid { + let string: &str = string_view_array.value(idx); + let n = n_array.value(idx); + + // Input string comes from StringViewArray, so it should fit in 32-bit length + let range = F::slice(string, n); + let result_bytes = &string.as_bytes()[range.clone()]; + + let byte_view = ByteView::from(view); + // New offsets starts at 0 for left, and at `range.start` for right, Review Comment: ```suggestion // New offset starts at 0 for left, and at `range.start` for right, ``` -- This is an automated message from the Apache Git Service. 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