parquet/arrow/buffer/
dictionary_buffer.rs

1// Licensed to the Apache Software Foundation (ASF) under one
2// or more contributor license agreements.  See the NOTICE file
3// distributed with this work for additional information
4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
6// "License"); you may not use this file except in compliance
7// with the License.  You may obtain a copy of the License at
8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
11// Unless required by applicable law or agreed to in writing,
12// software distributed under the License is distributed on an
13// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18use crate::arrow::buffer::offset_buffer::OffsetBuffer;
19use crate::arrow::record_reader::buffer::ValuesBuffer;
20use crate::errors::{ParquetError, Result};
21use arrow_array::{make_array, Array, ArrayRef, OffsetSizeTrait};
22use arrow_buffer::{ArrowNativeType, Buffer};
23use arrow_data::ArrayDataBuilder;
24use arrow_schema::DataType as ArrowType;
25use std::sync::Arc;
26
27/// An array of variable length byte arrays that are potentially dictionary encoded
28/// and can be converted into a corresponding [`ArrayRef`]
29pub enum DictionaryBuffer<K: ArrowNativeType, V: OffsetSizeTrait> {
30    Dict { keys: Vec<K>, values: ArrayRef },
31    Values { values: OffsetBuffer<V> },
32}
33
34impl<K: ArrowNativeType, V: OffsetSizeTrait> Default for DictionaryBuffer<K, V> {
35    fn default() -> Self {
36        Self::Values {
37            values: Default::default(),
38        }
39    }
40}
41
42impl<K: ArrowNativeType + Ord, V: OffsetSizeTrait> DictionaryBuffer<K, V> {
43    #[allow(unused)]
44    pub fn len(&self) -> usize {
45        match self {
46            Self::Dict { keys, .. } => keys.len(),
47            Self::Values { values } => values.len(),
48        }
49    }
50
51    /// Returns a mutable reference to a keys array
52    ///
53    /// Returns None if the dictionary needs to be recomputed
54    ///
55    /// # Panic
56    ///
57    /// Panics if the dictionary is too large for `K`
58    pub fn as_keys(&mut self, dictionary: &ArrayRef) -> Option<&mut Vec<K>> {
59        assert!(K::from_usize(dictionary.len()).is_some());
60
61        match self {
62            Self::Dict { keys, values } => {
63                // Need to discard fat pointer for equality check
64                // - https://stackoverflow.com/a/67114787
65                // - https://github.com/rust-lang/rust/issues/46139
66                let values_ptr = values.as_ref() as *const _ as *const ();
67                let dict_ptr = dictionary.as_ref() as *const _ as *const ();
68                if values_ptr == dict_ptr {
69                    Some(keys)
70                } else if keys.is_empty() {
71                    *values = Arc::clone(dictionary);
72                    Some(keys)
73                } else {
74                    None
75                }
76            }
77            Self::Values { values } if values.is_empty() => {
78                *self = Self::Dict {
79                    keys: Default::default(),
80                    values: Arc::clone(dictionary),
81                };
82                match self {
83                    Self::Dict { keys, .. } => Some(keys),
84                    _ => unreachable!(),
85                }
86            }
87            _ => None,
88        }
89    }
90
91    /// Returns a mutable reference to a values array
92    ///
93    /// If this is currently dictionary encoded, this will convert from the
94    /// dictionary encoded representation
95    pub fn spill_values(&mut self) -> Result<&mut OffsetBuffer<V>> {
96        match self {
97            Self::Values { values } => Ok(values),
98            Self::Dict { keys, values } => {
99                let mut spilled = OffsetBuffer::default();
100                let data = values.to_data();
101                let dict_buffers = data.buffers();
102                let dict_offsets = dict_buffers[0].typed_data::<V>();
103                let dict_values = dict_buffers[1].as_slice();
104
105                if values.is_empty() {
106                    // If dictionary is empty, zero pad offsets
107                    spilled.offsets.resize(keys.len() + 1, V::default());
108                } else {
109                    // Note: at this point null positions will have arbitrary dictionary keys
110                    // and this will hydrate them to the corresponding byte array. This is
111                    // likely sub-optimal, as we would prefer zero length null "slots", but
112                    // spilling is already a degenerate case and so it is unclear if this is
113                    // worth optimising for, e.g. by keeping a null mask around
114                    spilled.extend_from_dictionary(keys.as_slice(), dict_offsets, dict_values)?;
115                }
116
117                *self = Self::Values { values: spilled };
118                match self {
119                    Self::Values { values } => Ok(values),
120                    _ => unreachable!(),
121                }
122            }
123        }
124    }
125
126    /// Converts this into an [`ArrayRef`] with the provided `data_type` and `null_buffer`
127    pub fn into_array(
128        self,
129        null_buffer: Option<Buffer>,
130        data_type: &ArrowType,
131    ) -> Result<ArrayRef> {
132        assert!(matches!(data_type, ArrowType::Dictionary(_, _)));
133
134        match self {
135            Self::Dict { keys, values } => {
136                // Validate keys unless dictionary is empty
137                if !values.is_empty() {
138                    let min = K::from_usize(0).unwrap();
139                    let max = K::from_usize(values.len()).unwrap();
140
141                    // using copied and fold gets auto-vectorized since rust 1.70
142                    // all/any would allow early exit on invalid values
143                    // but in the happy case all values have to be checked anyway
144                    if !keys
145                        .as_slice()
146                        .iter()
147                        .copied()
148                        .fold(true, |a, x| a && x >= min && x < max)
149                    {
150                        return Err(general_err!(
151                            "dictionary key beyond bounds of dictionary: 0..{}",
152                            values.len()
153                        ));
154                    }
155                }
156
157                let builder = ArrayDataBuilder::new(data_type.clone())
158                    .len(keys.len())
159                    .add_buffer(Buffer::from_vec(keys))
160                    .add_child_data(values.into_data())
161                    .null_bit_buffer(null_buffer);
162
163                let data = match cfg!(debug_assertions) {
164                    true => builder.build().unwrap(),
165                    false => unsafe { builder.build_unchecked() },
166                };
167
168                Ok(make_array(data))
169            }
170            Self::Values { values } => {
171                let value_type = match data_type {
172                    ArrowType::Dictionary(_, v) => v.as_ref().clone(),
173                    _ => unreachable!(),
174                };
175
176                // This will compute a new dictionary
177                let array =
178                    arrow_cast::cast(&values.into_array(null_buffer, value_type), data_type)
179                        .expect("cast should be infallible");
180
181                Ok(array)
182            }
183        }
184    }
185}
186
187impl<K: ArrowNativeType, V: OffsetSizeTrait> ValuesBuffer for DictionaryBuffer<K, V> {
188    fn pad_nulls(
189        &mut self,
190        read_offset: usize,
191        values_read: usize,
192        levels_read: usize,
193        valid_mask: &[u8],
194    ) {
195        match self {
196            Self::Dict { keys, .. } => {
197                keys.resize(read_offset + levels_read, K::default());
198                keys.pad_nulls(read_offset, values_read, levels_read, valid_mask)
199            }
200            Self::Values { values, .. } => {
201                values.pad_nulls(read_offset, values_read, levels_read, valid_mask)
202            }
203        }
204    }
205}
206
207#[cfg(test)]
208mod tests {
209    use super::*;
210    use arrow::compute::cast;
211    use arrow_array::StringArray;
212
213    #[test]
214    fn test_dictionary_buffer() {
215        let dict_type =
216            ArrowType::Dictionary(Box::new(ArrowType::Int32), Box::new(ArrowType::Utf8));
217
218        let d1: ArrayRef = Arc::new(StringArray::from(vec!["hello", "world", "", "a", "b"]));
219
220        let mut buffer = DictionaryBuffer::<i32, i32>::default();
221
222        // Read some data preserving the dictionary
223        let values = &[1, 0, 3, 2, 4];
224        buffer.as_keys(&d1).unwrap().extend_from_slice(values);
225
226        let mut valid = vec![false, false, true, true, false, true, true, true];
227        let valid_buffer = Buffer::from_iter(valid.iter().cloned());
228        buffer.pad_nulls(0, values.len(), valid.len(), valid_buffer.as_slice());
229
230        // Read some data not preserving the dictionary
231
232        let values = buffer.spill_values().unwrap();
233        let read_offset = values.len();
234        values.try_push("bingo".as_bytes(), false).unwrap();
235        values.try_push("bongo".as_bytes(), false).unwrap();
236
237        valid.extend_from_slice(&[false, false, true, false, true]);
238        let null_buffer = Buffer::from_iter(valid.iter().cloned());
239        buffer.pad_nulls(read_offset, 2, 5, null_buffer.as_slice());
240
241        assert_eq!(buffer.len(), 13);
242        let split = std::mem::take(&mut buffer);
243
244        let array = split.into_array(Some(null_buffer), &dict_type).unwrap();
245        assert_eq!(array.data_type(), &dict_type);
246
247        let strings = cast(&array, &ArrowType::Utf8).unwrap();
248        let strings = strings.as_any().downcast_ref::<StringArray>().unwrap();
249        assert_eq!(
250            strings.iter().collect::<Vec<_>>(),
251            vec![
252                None,
253                None,
254                Some("world"),
255                Some("hello"),
256                None,
257                Some("a"),
258                Some(""),
259                Some("b"),
260                None,
261                None,
262                Some("bingo"),
263                None,
264                Some("bongo")
265            ]
266        );
267
268        // Can recreate with new dictionary as values is empty
269        assert!(matches!(&buffer, DictionaryBuffer::Values { .. }));
270        assert_eq!(buffer.len(), 0);
271        let d2 = Arc::new(StringArray::from(vec!["bingo", ""])) as ArrayRef;
272        buffer
273            .as_keys(&d2)
274            .unwrap()
275            .extend_from_slice(&[0, 1, 0, 1]);
276
277        let array = std::mem::take(&mut buffer)
278            .into_array(None, &dict_type)
279            .unwrap();
280        assert_eq!(array.data_type(), &dict_type);
281
282        let strings = cast(&array, &ArrowType::Utf8).unwrap();
283        let strings = strings.as_any().downcast_ref::<StringArray>().unwrap();
284        assert_eq!(
285            strings.iter().collect::<Vec<_>>(),
286            vec![Some("bingo"), Some(""), Some("bingo"), Some("")]
287        );
288
289        // Can recreate with new dictionary as keys empty
290        assert!(matches!(&buffer, DictionaryBuffer::Values { .. }));
291        assert_eq!(buffer.len(), 0);
292        let d3 = Arc::new(StringArray::from(vec!["bongo"])) as ArrayRef;
293        buffer.as_keys(&d3).unwrap().extend_from_slice(&[0, 0]);
294
295        // Cannot change dictionary as keys not empty
296        let d4 = Arc::new(StringArray::from(vec!["bananas"])) as ArrayRef;
297        assert!(buffer.as_keys(&d4).is_none());
298    }
299
300    #[test]
301    fn test_validates_keys() {
302        let dict_type =
303            ArrowType::Dictionary(Box::new(ArrowType::Int32), Box::new(ArrowType::Utf8));
304
305        let mut buffer = DictionaryBuffer::<i32, i32>::default();
306        let d = Arc::new(StringArray::from(vec!["", "f"])) as ArrayRef;
307        buffer.as_keys(&d).unwrap().extend_from_slice(&[0, 2, 0]);
308
309        let err = buffer.into_array(None, &dict_type).unwrap_err().to_string();
310        assert!(
311            err.contains("dictionary key beyond bounds of dictionary: 0..2"),
312            "{}",
313            err
314        );
315
316        let mut buffer = DictionaryBuffer::<i32, i32>::default();
317        let d = Arc::new(StringArray::from(vec![""])) as ArrayRef;
318        buffer.as_keys(&d).unwrap().extend_from_slice(&[0, 1, 0]);
319
320        let err = buffer.spill_values().unwrap_err().to_string();
321        assert!(
322            err.contains("dictionary key beyond bounds of dictionary: 0..1"),
323            "{}",
324            err
325        );
326    }
327}
parquet/arrow/buffer/dictionary_buffer.rs

parquet/arrow/buffer/
dictionary_buffer.rs
