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selection.rs
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selection.rs
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// 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::{Array, BooleanArray};
use arrow::compute::SlicesIterator;
use std::cmp::Ordering;
use std::collections::VecDeque;
use std::ops::Range;
/// [`RowSelection`] is a collection of [`RowSelector`] used to skip rows when
/// scanning a parquet file
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub struct RowSelector {
/// The number of rows
pub row_count: usize,
/// If true, skip `row_count` rows
pub skip: bool,
}
impl RowSelector {
/// Select `row_count` rows
pub fn select(row_count: usize) -> Self {
Self {
row_count,
skip: false,
}
}
/// Skip `row_count` rows
pub fn skip(row_count: usize) -> Self {
Self {
row_count,
skip: true,
}
}
}
/// [`RowSelection`] allows selecting or skipping a provided number of rows
/// when scanning the parquet file.
///
/// This is applied prior to reading column data, and can therefore
/// be used to skip IO to fetch data into memory
///
/// A typical use-case would be using the [`PageIndex`] to filter out rows
/// that don't satisfy a predicate
///
/// [`PageIndex`]: [crate::file::page_index::index::PageIndex]
#[derive(Debug, Clone, Default, Eq, PartialEq)]
pub struct RowSelection {
selectors: Vec<RowSelector>,
}
impl RowSelection {
/// Creates a [`RowSelection`] from a slice of [`BooleanArray`]
///
/// # Panic
///
/// Panics if any of the [`BooleanArray`] contain nulls
pub fn from_filters(filters: &[BooleanArray]) -> Self {
let mut next_offset = 0;
let total_rows = filters.iter().map(|x| x.len()).sum();
let iter = filters.iter().flat_map(|filter| {
let offset = next_offset;
next_offset += filter.len();
assert_eq!(filter.null_count(), 0);
SlicesIterator::new(filter)
.map(move |(start, end)| start + offset..end + offset)
});
Self::from_consecutive_ranges(iter, total_rows)
}
/// Creates a [`RowSelection`] from an iterator of consecutive ranges to keep
fn from_consecutive_ranges<I: Iterator<Item = Range<usize>>>(
ranges: I,
total_rows: usize,
) -> Self {
let mut selectors: Vec<RowSelector> = Vec::with_capacity(ranges.size_hint().0);
let mut last_end = 0;
for range in ranges {
let len = range.end - range.start;
match range.start.cmp(&last_end) {
Ordering::Equal => match selectors.last_mut() {
Some(last) => last.row_count += len,
None => selectors.push(RowSelector::select(len)),
},
Ordering::Greater => {
selectors.push(RowSelector::skip(range.start - last_end));
selectors.push(RowSelector::select(len))
}
Ordering::Less => panic!("out of order"),
}
last_end = range.end;
}
if last_end != total_rows {
selectors.push(RowSelector::skip(total_rows - last_end))
}
Self { selectors }
}
/// Given an offset index, return the offset ranges for all data pages selected by `self`
#[cfg(any(test, feature = "async"))]
pub(crate) fn scan_ranges(
&self,
page_locations: &[crate::format::PageLocation],
) -> Vec<Range<usize>> {
let mut ranges = vec![];
let mut row_offset = 0;
let mut pages = page_locations.iter().peekable();
let mut selectors = self.selectors.iter().cloned();
let mut current_selector = selectors.next();
let mut current_page = pages.next();
let mut current_page_included = false;
while let Some((selector, page)) = current_selector.as_mut().zip(current_page) {
if !(selector.skip || current_page_included) {
let start = page.offset as usize;
let end = start + page.compressed_page_size as usize;
ranges.push(start..end);
current_page_included = true;
}
if let Some(next_page) = pages.peek() {
if row_offset + selector.row_count > next_page.first_row_index as usize {
let remaining_in_page =
next_page.first_row_index as usize - row_offset;
selector.row_count -= remaining_in_page;
row_offset += remaining_in_page;
current_page = pages.next();
current_page_included = false;
continue;
} else {
if row_offset + selector.row_count
== next_page.first_row_index as usize
{
current_page = pages.next();
current_page_included = false;
}
row_offset += selector.row_count;
current_selector = selectors.next();
}
} else {
if !(selector.skip || current_page_included) {
let start = page.offset as usize;
let end = start + page.compressed_page_size as usize;
ranges.push(start..end);
}
current_selector = selectors.next()
}
}
ranges
}
/// Splits off the first `row_count` from this [`RowSelection`]
pub fn split_off(&mut self, row_count: usize) -> Self {
let mut total_count = 0;
// Find the index where the selector exceeds the row count
let find = self.selectors.iter().enumerate().find(|(_, selector)| {
total_count += selector.row_count;
total_count > row_count
});
let split_idx = match find {
Some((idx, _)) => idx,
None => {
let selectors = std::mem::take(&mut self.selectors);
return Self { selectors };
}
};
let mut remaining = self.selectors.split_off(split_idx);
// Always present as `split_idx < self.selectors.len`
let next = remaining.first_mut().unwrap();
let overflow = total_count - row_count;
if next.row_count != overflow {
self.selectors.push(RowSelector {
row_count: next.row_count - overflow,
skip: next.skip,
})
}
next.row_count = overflow;
std::mem::swap(&mut remaining, &mut self.selectors);
Self {
selectors: remaining,
}
}
/// Given a [`RowSelection`] computed under `self`, returns the [`RowSelection`]
/// representing their conjunction
///
/// For example:
///
/// self: NNNNNNNNNNNNYYYYYYYYYYYYYYYYYYYYYYNNNYYYYY
/// other: YYYYYNNNNYYYYYYYYYYYYY YYNNN
///
/// returned: NNNNNNNNNNNNYYYYYNNNNYYYYYYYYYYYYYNNNYYNNN
///
///
pub fn and_then(&self, other: &Self) -> Self {
let mut selectors = vec![];
let mut first = self.selectors.iter().cloned().peekable();
let mut second = other.selectors.iter().cloned().peekable();
let mut to_skip = 0;
while let Some(b) = second.peek_mut() {
let a = first.peek_mut().unwrap();
if b.row_count == 0 {
second.next().unwrap();
continue;
}
if a.row_count == 0 {
first.next().unwrap();
continue;
}
if a.skip {
// Records were skipped when producing second
to_skip += a.row_count;
first.next().unwrap();
continue;
}
let skip = b.skip;
let to_process = a.row_count.min(b.row_count);
a.row_count -= to_process;
b.row_count -= to_process;
match skip {
true => to_skip += to_process,
false => {
if to_skip != 0 {
selectors.push(RowSelector::skip(to_skip));
to_skip = 0;
}
selectors.push(RowSelector::select(to_process))
}
}
}
for v in first {
if v.row_count != 0 {
assert!(v.skip);
to_skip += v.row_count
}
}
if to_skip != 0 {
selectors.push(RowSelector::skip(to_skip));
}
Self { selectors }
}
/// Returns `true` if this [`RowSelection`] selects any rows
pub fn selects_any(&self) -> bool {
self.selectors.iter().any(|x| !x.skip)
}
}
impl From<Vec<RowSelector>> for RowSelection {
fn from(selectors: Vec<RowSelector>) -> Self {
Self { selectors }
}
}
impl From<RowSelection> for VecDeque<RowSelector> {
fn from(r: RowSelection) -> Self {
r.selectors.into()
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::format::PageLocation;
use rand::{thread_rng, Rng};
#[test]
fn test_from_filters() {
let filters = vec![
BooleanArray::from(vec![false, false, false, true, true, true, true]),
BooleanArray::from(vec![true, true, false, false, true, true, true]),
BooleanArray::from(vec![false, false, false, false]),
BooleanArray::from(Vec::<bool>::new()),
];
let selection = RowSelection::from_filters(&filters[..1]);
assert!(selection.selects_any());
assert_eq!(
selection.selectors,
vec![RowSelector::skip(3), RowSelector::select(4)]
);
let selection = RowSelection::from_filters(&filters[..2]);
assert!(selection.selects_any());
assert_eq!(
selection.selectors,
vec![
RowSelector::skip(3),
RowSelector::select(6),
RowSelector::skip(2),
RowSelector::select(3)
]
);
let selection = RowSelection::from_filters(&filters);
assert!(selection.selects_any());
assert_eq!(
selection.selectors,
vec![
RowSelector::skip(3),
RowSelector::select(6),
RowSelector::skip(2),
RowSelector::select(3),
RowSelector::skip(4)
]
);
let selection = RowSelection::from_filters(&filters[2..3]);
assert!(!selection.selects_any());
assert_eq!(selection.selectors, vec![RowSelector::skip(4)]);
}
#[test]
fn test_split_off() {
let mut selection = RowSelection::from(vec![
RowSelector::skip(34),
RowSelector::select(12),
RowSelector::skip(3),
RowSelector::select(35),
]);
let split = selection.split_off(34);
assert_eq!(split.selectors, vec![RowSelector::skip(34)]);
assert_eq!(
selection.selectors,
vec![
RowSelector::select(12),
RowSelector::skip(3),
RowSelector::select(35)
]
);
let split = selection.split_off(5);
assert_eq!(split.selectors, vec![RowSelector::select(5)]);
assert_eq!(
selection.selectors,
vec![
RowSelector::select(7),
RowSelector::skip(3),
RowSelector::select(35)
]
);
let split = selection.split_off(8);
assert_eq!(
split.selectors,
vec![RowSelector::select(7), RowSelector::skip(1)]
);
assert_eq!(
selection.selectors,
vec![RowSelector::skip(2), RowSelector::select(35)]
);
let split = selection.split_off(200);
assert_eq!(
split.selectors,
vec![RowSelector::skip(2), RowSelector::select(35)]
);
assert!(selection.selectors.is_empty());
}
#[test]
fn test_and() {
let mut a = RowSelection::from(vec![
RowSelector::skip(12),
RowSelector::select(23),
RowSelector::skip(3),
RowSelector::select(5),
]);
let b = RowSelection::from(vec![
RowSelector::select(5),
RowSelector::skip(4),
RowSelector::select(15),
RowSelector::skip(4),
]);
let mut expected = RowSelection::from(vec![
RowSelector::skip(12),
RowSelector::select(5),
RowSelector::skip(4),
RowSelector::select(14),
RowSelector::skip(3),
RowSelector::select(1),
RowSelector::skip(4),
]);
assert_eq!(a.and_then(&b), expected);
a.split_off(7);
expected.split_off(7);
assert_eq!(a.and_then(&b), expected);
let a = RowSelection::from(vec![RowSelector::select(5), RowSelector::skip(3)]);
let b = RowSelection::from(vec![
RowSelector::select(2),
RowSelector::skip(1),
RowSelector::select(1),
RowSelector::skip(1),
]);
assert_eq!(
a.and_then(&b).selectors,
vec![
RowSelector::select(2),
RowSelector::skip(1),
RowSelector::select(1),
RowSelector::skip(4)
]
);
}
#[test]
fn test_and_fuzz() {
let mut rand = thread_rng();
for _ in 0..100 {
let a_len = rand.gen_range(10..100);
let a_bools: Vec<_> = (0..a_len).map(|_| rand.gen_bool(0.2)).collect();
let a = RowSelection::from_filters(&[BooleanArray::from(a_bools.clone())]);
let b_len: usize = a_bools.iter().map(|x| *x as usize).sum();
let b_bools: Vec<_> = (0..b_len).map(|_| rand.gen_bool(0.8)).collect();
let b = RowSelection::from_filters(&[BooleanArray::from(b_bools.clone())]);
let mut expected_bools = vec![false; a_len];
let mut iter_b = b_bools.iter();
for (idx, b) in a_bools.iter().enumerate() {
if *b && *iter_b.next().unwrap() {
expected_bools[idx] = true;
}
}
let expected =
RowSelection::from_filters(&[BooleanArray::from(expected_bools)]);
let total_rows: usize = expected.selectors.iter().map(|s| s.row_count).sum();
assert_eq!(a_len, total_rows);
assert_eq!(a.and_then(&b), expected);
}
}
#[test]
fn test_scan_ranges() {
let index = vec![
PageLocation {
offset: 0,
compressed_page_size: 10,
first_row_index: 0,
},
PageLocation {
offset: 10,
compressed_page_size: 10,
first_row_index: 10,
},
PageLocation {
offset: 20,
compressed_page_size: 10,
first_row_index: 20,
},
PageLocation {
offset: 30,
compressed_page_size: 10,
first_row_index: 30,
},
PageLocation {
offset: 40,
compressed_page_size: 10,
first_row_index: 40,
},
PageLocation {
offset: 50,
compressed_page_size: 10,
first_row_index: 50,
},
PageLocation {
offset: 60,
compressed_page_size: 10,
first_row_index: 60,
},
];
let selection = RowSelection::from(vec![
// Skip first page
RowSelector::skip(10),
// Multiple selects in same page
RowSelector::select(3),
RowSelector::skip(3),
RowSelector::select(4),
// Select to page boundary
RowSelector::skip(5),
RowSelector::select(5),
// Skip full page past page boundary
RowSelector::skip(12),
// Select across page boundaries
RowSelector::select(12),
// Skip final page
RowSelector::skip(12),
]);
let ranges = selection.scan_ranges(&index);
// assert_eq!(mask, vec![false, true, true, false, true, true, false]);
assert_eq!(ranges, vec![10..20, 20..30, 40..50, 50..60]);
let selection = RowSelection::from(vec![
// Skip first page
RowSelector::skip(10),
// Multiple selects in same page
RowSelector::select(3),
RowSelector::skip(3),
RowSelector::select(4),
// Select to page boundary
RowSelector::skip(5),
RowSelector::select(5),
// Skip full page past page boundary
RowSelector::skip(12),
// Select across page boundaries
RowSelector::select(12),
RowSelector::skip(1),
// Select across page boundaries including final page
RowSelector::select(8),
]);
let ranges = selection.scan_ranges(&index);
// assert_eq!(mask, vec![false, true, true, false, true, true, true]);
assert_eq!(ranges, vec![10..20, 20..30, 40..50, 50..60, 60..70]);
let selection = RowSelection::from(vec![
// Skip first page
RowSelector::skip(10),
// Multiple selects in same page
RowSelector::select(3),
RowSelector::skip(3),
RowSelector::select(4),
// Select to page boundary
RowSelector::skip(5),
RowSelector::select(5),
// Skip full page past page boundary
RowSelector::skip(12),
// Select to final page bounday
RowSelector::select(12),
RowSelector::skip(1),
// Skip across final page boundary
RowSelector::skip(8),
// Select from final page
RowSelector::select(4),
]);
let ranges = selection.scan_ranges(&index);
// assert_eq!(mask, vec![false, true, true, false, true, true, true]);
assert_eq!(ranges, vec![10..20, 20..30, 40..50, 50..60, 60..70]);
let selection = RowSelection::from(vec![
// Skip first page
RowSelector::skip(10),
// Multiple selects in same page
RowSelector::select(3),
RowSelector::skip(3),
RowSelector::select(4),
// Select to remaining in page and first row of next page
RowSelector::skip(5),
RowSelector::select(6),
// Skip remaining
RowSelector::skip(50),
]);
let ranges = selection.scan_ranges(&index);
// assert_eq!(mask, vec![false, true, true, false, true, true, true]);
assert_eq!(ranges, vec![10..20, 20..30, 30..40]);
}
}