datafusion_physical_expr_common/binary_view_map.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.
//! [`ArrowBytesViewMap`] and [`ArrowBytesViewSet`] for storing maps/sets of values from
//! `StringViewArray`/`BinaryViewArray`.
//! Much of the code is from `binary_map.rs`, but with simpler implementation because we directly use the
//! [`GenericByteViewBuilder`].
use ahash::RandomState;
use arrow::array::cast::AsArray;
use arrow::array::{Array, ArrayBuilder, ArrayRef, GenericByteViewBuilder};
use arrow::datatypes::{BinaryViewType, ByteViewType, DataType, StringViewType};
use datafusion_common::hash_utils::create_hashes;
use datafusion_common::utils::proxy::{RawTableAllocExt, VecAllocExt};
use std::fmt::Debug;
use std::sync::Arc;
use crate::binary_map::OutputType;
/// HashSet optimized for storing string or binary values that can produce that
/// the final set as a `GenericBinaryViewArray` with minimal copies.
#[derive(Debug)]
pub struct ArrowBytesViewSet(ArrowBytesViewMap<()>);
impl ArrowBytesViewSet {
pub fn new(output_type: OutputType) -> Self {
Self(ArrowBytesViewMap::new(output_type))
}
/// Inserts each value from `values` into the set
pub fn insert(&mut self, values: &ArrayRef) {
fn make_payload_fn(_value: Option<&[u8]>) {}
fn observe_payload_fn(_payload: ()) {}
self.0
.insert_if_new(values, make_payload_fn, observe_payload_fn);
}
/// Return the contents of this map and replace it with a new empty map with
/// the same output type
pub fn take(&mut self) -> Self {
let mut new_self = Self::new(self.0.output_type);
std::mem::swap(self, &mut new_self);
new_self
}
/// Converts this set into a `StringViewArray` or `BinaryViewArray`
/// containing each distinct value that was interned.
/// This is done without copying the values.
pub fn into_state(self) -> ArrayRef {
self.0.into_state()
}
/// Returns the total number of distinct values (including nulls) seen so far
pub fn len(&self) -> usize {
self.0.len()
}
pub fn is_empty(&self) -> bool {
self.0.is_empty()
}
/// returns the total number of distinct values (not including nulls) seen so far
pub fn non_null_len(&self) -> usize {
self.0.non_null_len()
}
/// Return the total size, in bytes, of memory used to store the data in
/// this set, not including `self`
pub fn size(&self) -> usize {
self.0.size()
}
}
/// Optimized map for storing Arrow "byte view" types (`StringView`, `BinaryView`)
/// values that can produce the set of keys on
/// output as `GenericBinaryViewArray` without copies.
///
/// Equivalent to `HashSet<String, V>` but with better performance if you need
/// to emit the keys as an Arrow `StringViewArray` / `BinaryViewArray`. For other
/// purposes it is the same as a `HashMap<String, V>`
///
/// # Generic Arguments
///
/// * `V`: payload type
///
/// # Description
///
/// This is a specialized HashMap with the following properties:
///
/// 1. Optimized for storing and emitting Arrow byte types (e.g.
/// `StringViewArray` / `BinaryViewArray`) very efficiently by minimizing copying of
/// the string values themselves, both when inserting and when emitting the
/// final array.
///
/// 2. Retains the insertion order of entries in the final array. The values are
/// in the same order as they were inserted.
///
/// Note this structure can be used as a `HashSet` by specifying the value type
/// as `()`, as is done by [`ArrowBytesViewSet`].
///
/// This map is used by the special `COUNT DISTINCT` aggregate function to
/// store the distinct values, and by the `GROUP BY` operator to store
/// group values when they are a single string array.
pub struct ArrowBytesViewMap<V>
where
V: Debug + PartialEq + Eq + Clone + Copy + Default,
{
/// Should the output be StringView or BinaryView?
output_type: OutputType,
/// Underlying hash set for each distinct value
map: hashbrown::raw::RawTable<Entry<V>>,
/// Total size of the map in bytes
map_size: usize,
/// Builder for output array
builder: GenericByteViewBuilder<BinaryViewType>,
/// random state used to generate hashes
random_state: RandomState,
/// buffer that stores hash values (reused across batches to save allocations)
hashes_buffer: Vec<u64>,
/// `(payload, null_index)` for the 'null' value, if any
/// NOTE null_index is the logical index in the final array, not the index
/// in the buffer
null: Option<(V, usize)>,
}
/// The size, in number of entries, of the initial hash table
const INITIAL_MAP_CAPACITY: usize = 512;
impl<V> ArrowBytesViewMap<V>
where
V: Debug + PartialEq + Eq + Clone + Copy + Default,
{
pub fn new(output_type: OutputType) -> Self {
Self {
output_type,
map: hashbrown::raw::RawTable::with_capacity(INITIAL_MAP_CAPACITY),
map_size: 0,
builder: GenericByteViewBuilder::new(),
random_state: RandomState::new(),
hashes_buffer: vec![],
null: None,
}
}
/// Return the contents of this map and replace it with a new empty map with
/// the same output type
pub fn take(&mut self) -> Self {
let mut new_self = Self::new(self.output_type);
std::mem::swap(self, &mut new_self);
new_self
}
/// Inserts each value from `values` into the map, invoking `payload_fn` for
/// each value if *not* already present, deferring the allocation of the
/// payload until it is needed.
///
/// Note that this is different than a normal map that would replace the
/// existing entry
///
/// # Arguments:
///
/// `values`: array whose values are inserted
///
/// `make_payload_fn`: invoked for each value that is not already present
/// to create the payload, in order of the values in `values`
///
/// `observe_payload_fn`: invoked once, for each value in `values`, that was
/// already present in the map, with corresponding payload value.
///
/// # Returns
///
/// The payload value for the entry, either the existing value or
/// the newly inserted value
///
/// # Safety:
///
/// Note that `make_payload_fn` and `observe_payload_fn` are only invoked
/// with valid values from `values`, not for the `NULL` value.
pub fn insert_if_new<MP, OP>(
&mut self,
values: &ArrayRef,
make_payload_fn: MP,
observe_payload_fn: OP,
) where
MP: FnMut(Option<&[u8]>) -> V,
OP: FnMut(V),
{
// Sanity check array type
match self.output_type {
OutputType::BinaryView => {
assert!(matches!(values.data_type(), DataType::BinaryView));
self.insert_if_new_inner::<MP, OP, BinaryViewType>(
values,
make_payload_fn,
observe_payload_fn,
)
}
OutputType::Utf8View => {
assert!(matches!(values.data_type(), DataType::Utf8View));
self.insert_if_new_inner::<MP, OP, StringViewType>(
values,
make_payload_fn,
observe_payload_fn,
)
}
_ => unreachable!("Utf8/Binary should use `ArrowBytesSet`"),
};
}
/// Generic version of [`Self::insert_if_new`] that handles `ByteViewType`
/// (both StringView and BinaryView)
///
/// Note this is the only function that is generic on [`ByteViewType`], which
/// avoids having to template the entire structure, making the code
/// simpler and understand and reducing code bloat due to duplication.
///
/// See comments on `insert_if_new` for more details
fn insert_if_new_inner<MP, OP, B>(
&mut self,
values: &ArrayRef,
mut make_payload_fn: MP,
mut observe_payload_fn: OP,
) where
MP: FnMut(Option<&[u8]>) -> V,
OP: FnMut(V),
B: ByteViewType,
{
// step 1: compute hashes
let batch_hashes = &mut self.hashes_buffer;
batch_hashes.clear();
batch_hashes.resize(values.len(), 0);
create_hashes(&[values.clone()], &self.random_state, batch_hashes)
// hash is supported for all types and create_hashes only
// returns errors for unsupported types
.unwrap();
// step 2: insert each value into the set, if not already present
let values = values.as_byte_view::<B>();
// Ensure lengths are equivalent
assert_eq!(values.len(), batch_hashes.len());
for (value, &hash) in values.iter().zip(batch_hashes.iter()) {
// handle null value
let Some(value) = value else {
let payload = if let Some(&(payload, _offset)) = self.null.as_ref() {
payload
} else {
let payload = make_payload_fn(None);
let null_index = self.builder.len();
self.builder.append_null();
self.null = Some((payload, null_index));
payload
};
observe_payload_fn(payload);
continue;
};
// get the value as bytes
let value: &[u8] = value.as_ref();
let entry = self.map.get_mut(hash, |header| {
let v = self.builder.get_value(header.view_idx);
if v.len() != value.len() {
return false;
}
v == value
});
let payload = if let Some(entry) = entry {
entry.payload
} else {
// no existing value, make a new one.
let payload = make_payload_fn(Some(value));
let inner_view_idx = self.builder.len();
let new_header = Entry {
view_idx: inner_view_idx,
hash,
payload,
};
self.builder.append_value(value);
self.map
.insert_accounted(new_header, |h| h.hash, &mut self.map_size);
payload
};
observe_payload_fn(payload);
}
}
/// Converts this set into a `StringViewArray`, or `BinaryViewArray`,
/// containing each distinct value
/// that was inserted. This is done without copying the values.
///
/// The values are guaranteed to be returned in the same order in which
/// they were first seen.
pub fn into_state(self) -> ArrayRef {
let mut builder = self.builder;
match self.output_type {
OutputType::BinaryView => {
let array = builder.finish();
Arc::new(array)
}
OutputType::Utf8View => {
// SAFETY:
// we asserted the input arrays were all the correct type and
// thus since all the values that went in were valid (e.g. utf8)
// so are all the values that come out
let array = builder.finish();
let array = unsafe { array.to_string_view_unchecked() };
Arc::new(array)
}
_ => {
unreachable!("Utf8/Binary should use `ArrowBytesMap`")
}
}
}
/// Total number of entries (including null, if present)
pub fn len(&self) -> usize {
self.non_null_len() + self.null.map(|_| 1).unwrap_or(0)
}
/// Is the set empty?
pub fn is_empty(&self) -> bool {
self.map.is_empty() && self.null.is_none()
}
/// Number of non null entries
pub fn non_null_len(&self) -> usize {
self.map.len()
}
/// Return the total size, in bytes, of memory used to store the data in
/// this set, not including `self`
pub fn size(&self) -> usize {
self.map_size
+ self.builder.allocated_size()
+ self.hashes_buffer.allocated_size()
}
}
impl<V> Debug for ArrowBytesViewMap<V>
where
V: Debug + PartialEq + Eq + Clone + Copy + Default,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("ArrowBytesMap")
.field("map", &"<map>")
.field("map_size", &self.map_size)
.field("view_builder", &self.builder)
.field("random_state", &self.random_state)
.field("hashes_buffer", &self.hashes_buffer)
.finish()
}
}
/// Entry in the hash table -- see [`ArrowBytesViewMap`] for more details
#[derive(Debug, PartialEq, Eq, Hash, Clone, Copy)]
struct Entry<V>
where
V: Debug + PartialEq + Eq + Clone + Copy + Default,
{
/// The idx into the views array
view_idx: usize,
hash: u64,
/// value stored by the entry
payload: V,
}
#[cfg(test)]
mod tests {
use arrow::array::{BinaryViewArray, GenericByteViewArray, StringViewArray};
use hashbrown::HashMap;
use super::*;
// asserts that the set contains the expected strings, in the same order
fn assert_set(set: ArrowBytesViewSet, expected: &[Option<&str>]) {
let strings = set.into_state();
let strings = strings.as_string_view();
let state = strings.into_iter().collect::<Vec<_>>();
assert_eq!(state, expected);
}
#[test]
fn string_view_set_empty() {
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let array: ArrayRef = Arc::new(StringViewArray::new_null(0));
set.insert(&array);
assert_eq!(set.len(), 0);
assert_eq!(set.non_null_len(), 0);
assert_set(set, &[]);
}
#[test]
fn string_view_set_one_null() {
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let array: ArrayRef = Arc::new(StringViewArray::new_null(1));
set.insert(&array);
assert_eq!(set.len(), 1);
assert_eq!(set.non_null_len(), 0);
assert_set(set, &[None]);
}
#[test]
fn string_view_set_many_null() {
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let array: ArrayRef = Arc::new(StringViewArray::new_null(11));
set.insert(&array);
assert_eq!(set.len(), 1);
assert_eq!(set.non_null_len(), 0);
assert_set(set, &[None]);
}
#[test]
fn test_string_view_set_basic() {
// basic test for mixed small and large string values
let values = GenericByteViewArray::from(vec![
Some("a"),
Some("b"),
Some("CXCCCCCCCCAABB"), // 14 bytes
Some(""),
Some("cbcxx"), // 5 bytes
None,
Some("AAAAAAAA"), // 8 bytes
Some("BBBBBQBBBAAA"), // 12 bytes
Some("a"),
Some("cbcxx"),
Some("b"),
Some("cbcxx"),
Some(""),
None,
Some("BBBBBQBBBAAA"),
Some("BBBBBQBBBAAA"),
Some("AAAAAAAA"),
Some("CXCCCCCCCCAABB"),
]);
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let array: ArrayRef = Arc::new(values);
set.insert(&array);
// values mut appear be in the order they were inserted
assert_set(
set,
&[
Some("a"),
Some("b"),
Some("CXCCCCCCCCAABB"),
Some(""),
Some("cbcxx"),
None,
Some("AAAAAAAA"),
Some("BBBBBQBBBAAA"),
],
);
}
#[test]
fn test_string_set_non_utf8() {
// basic test for mixed small and large string values
let values = GenericByteViewArray::from(vec![
Some("a"),
Some("✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥"),
Some("🔥"),
Some("✨✨✨"),
Some("foobarbaz"),
Some("🔥"),
Some("✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥"),
]);
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let array: ArrayRef = Arc::new(values);
set.insert(&array);
// strings mut appear be in the order they were inserted
assert_set(
set,
&[
Some("a"),
Some("✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥✨🔥"),
Some("🔥"),
Some("✨✨✨"),
Some("foobarbaz"),
],
);
}
// Test use of binary output type
#[test]
fn test_binary_set() {
let v: Vec<Option<&[u8]>> = vec![
Some(b"a"),
Some(b"CXCCCCCCCCCCCCC"),
None,
Some(b"CXCCCCCCCCCCCCC"),
];
let values: ArrayRef = Arc::new(BinaryViewArray::from(v));
let expected: Vec<Option<&[u8]>> =
vec![Some(b"a"), Some(b"CXCCCCCCCCCCCCC"), None];
let expected: ArrayRef = Arc::new(GenericByteViewArray::from(expected));
let mut set = ArrowBytesViewSet::new(OutputType::BinaryView);
set.insert(&values);
assert_eq!(&set.into_state(), &expected);
}
// inserting strings into the set does not increase reported memory
#[test]
fn test_string_set_memory_usage() {
let strings1 = StringViewArray::from(vec![
Some("a"),
Some("b"),
Some("CXCCCCCCCCCCC"), // 13 bytes
Some("AAAAAAAA"), // 8 bytes
Some("BBBBBQBBB"), // 9 bytes
]);
let total_strings1_len = strings1
.iter()
.map(|s| s.map(|s| s.len()).unwrap_or(0))
.sum::<usize>();
let values1: ArrayRef = Arc::new(StringViewArray::from(strings1));
// Much larger strings in strings2
let strings2 = StringViewArray::from(vec![
"FOO".repeat(1000),
"BAR larger than 12 bytes.".repeat(100_000),
"more unique.".repeat(1000),
"more unique2.".repeat(1000),
"FOO".repeat(3000),
]);
let total_strings2_len = strings2
.iter()
.map(|s| s.map(|s| s.len()).unwrap_or(0))
.sum::<usize>();
let values2: ArrayRef = Arc::new(StringViewArray::from(strings2));
let mut set = ArrowBytesViewSet::new(OutputType::Utf8View);
let size_empty = set.size();
set.insert(&values1);
let size_after_values1 = set.size();
assert!(size_empty < size_after_values1);
assert!(
size_after_values1 > total_strings1_len,
"expect {size_after_values1} to be more than {total_strings1_len}"
);
assert!(size_after_values1 < total_strings1_len + total_strings2_len);
// inserting the same strings should not affect the size
set.insert(&values1);
assert_eq!(set.size(), size_after_values1);
assert_eq!(set.len(), 5);
// inserting the large strings should increase the reported size
set.insert(&values2);
let size_after_values2 = set.size();
assert!(size_after_values2 > size_after_values1);
assert_eq!(set.len(), 10);
}
#[derive(Debug, PartialEq, Eq, Default, Clone, Copy)]
struct TestPayload {
// store the string value to check against input
index: usize, // store the index of the string (each new string gets the next sequential input)
}
/// Wraps an [`ArrowBytesViewMap`], validating its invariants
struct TestMap {
map: ArrowBytesViewMap<TestPayload>,
// stores distinct strings seen, in order
strings: Vec<Option<String>>,
// map strings to index in strings
indexes: HashMap<Option<String>, usize>,
}
impl TestMap {
/// creates a map with TestPayloads for the given strings and then
/// validates the payloads
fn new() -> Self {
Self {
map: ArrowBytesViewMap::new(OutputType::Utf8View),
strings: vec![],
indexes: HashMap::new(),
}
}
/// Inserts strings into the map
fn insert(&mut self, strings: &[Option<&str>]) {
let string_array = StringViewArray::from(strings.to_vec());
let arr: ArrayRef = Arc::new(string_array);
let mut next_index = self.indexes.len();
let mut actual_new_strings = vec![];
let mut actual_seen_indexes = vec![];
// update self with new values, keeping track of newly added values
for str in strings {
let str = str.map(|s| s.to_string());
let index = self.indexes.get(&str).cloned().unwrap_or_else(|| {
actual_new_strings.push(str.clone());
let index = self.strings.len();
self.strings.push(str.clone());
self.indexes.insert(str, index);
index
});
actual_seen_indexes.push(index);
}
// insert the values into the map, recording what we did
let mut seen_new_strings = vec![];
let mut seen_indexes = vec![];
self.map.insert_if_new(
&arr,
|s| {
let value = s
.map(|s| String::from_utf8(s.to_vec()).expect("Non utf8 string"));
let index = next_index;
next_index += 1;
seen_new_strings.push(value);
TestPayload { index }
},
|payload| {
seen_indexes.push(payload.index);
},
);
assert_eq!(actual_seen_indexes, seen_indexes);
assert_eq!(actual_new_strings, seen_new_strings);
}
/// Call `self.map.into_array()` validating that the strings are in the same
/// order as they were inserted
fn into_array(self) -> ArrayRef {
let Self {
map,
strings,
indexes: _,
} = self;
let arr = map.into_state();
let expected: ArrayRef = Arc::new(StringViewArray::from(strings));
assert_eq!(&arr, &expected);
arr
}
}
#[test]
fn test_map() {
let input = vec![
// Note mix of short/long strings
Some("A"),
Some("bcdefghijklmnop1234567"),
Some("X"),
Some("Y"),
None,
Some("qrstuvqxyzhjwya"),
Some("✨🔥"),
Some("🔥"),
Some("🔥🔥🔥🔥🔥🔥"),
];
let mut test_map = TestMap::new();
test_map.insert(&input);
test_map.insert(&input); // put it in twice
let expected_output: ArrayRef = Arc::new(StringViewArray::from(input));
assert_eq!(&test_map.into_array(), &expected_output);
}
}