lance_encoding/encodings/physical/
bitmap.rs

1// SPDX-License-Identifier: Apache-2.0
2// SPDX-FileCopyrightText: Copyright The Lance Authors
3
4use std::{ops::Range, sync::Arc};
5
6use arrow_buffer::BooleanBufferBuilder;
7use bytes::Bytes;
8
9use futures::{future::BoxFuture, FutureExt};
10use lance_core::Result;
11use log::trace;
12
13use crate::{
14    buffer::LanceBuffer,
15    data::{BlockInfo, DataBlock, FixedWidthDataBlock},
16    decoder::{PageScheduler, PrimitivePageDecoder},
17    EncodingsIo,
18};
19
20/// A physical scheduler for bitmap buffers encoded densely as 1 bit per value
21/// with bit-endianness(e.g. what Arrow uses for validity bitmaps and boolean arrays)
22///
23/// This decoder decodes from one buffer of disk data into one buffer of memory data
24#[derive(Debug, Clone, Copy)]
25pub struct DenseBitmapScheduler {
26    buffer_offset: u64,
27}
28
29impl DenseBitmapScheduler {
30    pub fn new(buffer_offset: u64) -> Self {
31        Self { buffer_offset }
32    }
33}
34
35impl PageScheduler for DenseBitmapScheduler {
36    fn schedule_ranges(
37        &self,
38        ranges: &[Range<u64>],
39        scheduler: &Arc<dyn EncodingsIo>,
40        top_level_row: u64,
41    ) -> BoxFuture<'static, Result<Box<dyn PrimitivePageDecoder>>> {
42        let mut min = u64::MAX;
43        let mut max = 0;
44        let chunk_reqs = ranges
45            .iter()
46            .map(|range| {
47                debug_assert_ne!(range.start, range.end);
48                let start = self.buffer_offset + range.start / 8;
49                let bit_offset = range.start % 8;
50                let end = self.buffer_offset + range.end.div_ceil(8);
51                let byte_range = start..end;
52                min = min.min(start);
53                max = max.max(end);
54                (byte_range, bit_offset, range.end - range.start)
55            })
56            .collect::<Vec<_>>();
57
58        let byte_ranges = chunk_reqs
59            .iter()
60            .map(|(range, _, _)| range.clone())
61            .collect::<Vec<_>>();
62        trace!(
63            "Scheduling I/O for {} ranges across byte range {}..{}",
64            byte_ranges.len(),
65            min,
66            max
67        );
68        let bytes = scheduler.submit_request(byte_ranges, top_level_row);
69
70        async move {
71            let bytes = bytes.await?;
72            let chunks = bytes
73                .into_iter()
74                .zip(chunk_reqs)
75                .map(|(bytes, (_, bit_offset, length))| BitmapData {
76                    data: bytes,
77                    bit_offset,
78                    length,
79                })
80                .collect::<Vec<_>>();
81            Ok(Box::new(BitmapDecoder { chunks }) as Box<dyn PrimitivePageDecoder>)
82        }
83        .boxed()
84    }
85}
86
87struct BitmapData {
88    data: Bytes,
89    bit_offset: u64,
90    length: u64,
91}
92
93struct BitmapDecoder {
94    chunks: Vec<BitmapData>,
95}
96
97impl PrimitivePageDecoder for BitmapDecoder {
98    fn decode(&self, rows_to_skip: u64, num_rows: u64) -> Result<DataBlock> {
99        let mut rows_to_skip = rows_to_skip;
100        let mut dest_builder = BooleanBufferBuilder::new(num_rows as usize);
101
102        let mut rows_remaining = num_rows;
103        for chunk in &self.chunks {
104            if chunk.length <= rows_to_skip {
105                rows_to_skip -= chunk.length;
106            } else {
107                let start = rows_to_skip + chunk.bit_offset;
108                let num_vals_to_take = rows_remaining.min(chunk.length);
109                let end = start + num_vals_to_take;
110                dest_builder.append_packed_range(start as usize..end as usize, &chunk.data);
111                rows_to_skip = 0;
112                rows_remaining -= num_vals_to_take;
113            }
114        }
115
116        let bool_buffer = dest_builder.finish().into_inner();
117        Ok(DataBlock::FixedWidth(FixedWidthDataBlock {
118            data: LanceBuffer::from(bool_buffer),
119            bits_per_value: 1,
120            num_values: num_rows,
121            block_info: BlockInfo::new(),
122        }))
123    }
124}
125
126#[cfg(test)]
127mod tests {
128
129    use arrow_schema::{DataType, Field};
130    use bytes::Bytes;
131
132    use crate::decoder::PrimitivePageDecoder;
133    use crate::encodings::physical::bitmap::BitmapData;
134    use crate::testing::check_round_trip_encoding_random;
135    use crate::version::LanceFileVersion;
136
137    use super::BitmapDecoder;
138
139    #[test_log::test(tokio::test)]
140    async fn test_bitmap_boolean() {
141        let field = Field::new("", DataType::Boolean, false);
142        check_round_trip_encoding_random(field, LanceFileVersion::V2_0).await;
143    }
144
145    #[test]
146    fn test_bitmap_decoder_edge_cases() {
147        // Regression for a case where the row skip and the bit offset
148        // require us to read from the second Bytes instead of the first
149        let decoder = BitmapDecoder {
150            chunks: vec![
151                BitmapData {
152                    data: Bytes::from_static(&[0b11111111]),
153                    bit_offset: 4,
154                    length: 4,
155                },
156                BitmapData {
157                    data: Bytes::from_static(&[0b00000000]),
158                    bit_offset: 4,
159                    length: 4,
160                },
161            ],
162        };
163
164        let result = decoder.decode(5, 1);
165        assert!(result.is_ok());
166    }
167}
lance_encoding/encodings/physical/bitmap.rs

lance_encoding/encodings/physical/
bitmap.rs
