Rich-T-kid commented on code in PR #21765: URL: https://github.com/apache/datafusion/pull/21765#discussion_r3364375245
########## datafusion/physical-plan/src/aggregates/group_values/single_group_by/dictionary.rs: ########## @@ -0,0 +1,783 @@ +// 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 crate::aggregates::group_values::GroupValues; +use crate::hash_utils::RandomState; +use arrow::array::{ + Array, ArrayRef, DictionaryArray, LargeStringArray, LargeStringBuilder, ListArray, + ListBuilder, PrimitiveArray, PrimitiveBuilder, StringArray, StringBuilder, + StringViewArray, StringViewBuilder, +}; +use arrow::datatypes::{ArrowDictionaryKeyType, ArrowNativeType, DataType}; +use datafusion_common::DataFusionError::{Internal, NotImplemented}; +use datafusion_common::Result; +use datafusion_common::hash_utils::create_hashes; +use datafusion_expr::EmitTo; +use hashbrown::HashTable; +use hashbrown::hash_table::Entry as HashTableEntry; +use std::borrow::Cow; +use std::marker::PhantomData; +use std::sync::Arc; + +/// Heuristic for sizing the values buffer of string builders during emit: +/// dictionary-encoded values are short by design (categorical strings, short +/// identifiers), so 16 B/item avoids the realloc-doubling chain in the common +/// case while keeping over-allocation cheap when values are smaller. +const AVG_BYTES_PER_DICT_VALUE: usize = 16; +const INITIAL_PRE_ALLOCATION: usize = 8 * 1024; // avoid re-allocation`s for small-medium groups + +macro_rules! decode_list { + ($raw:expr, $builder:expr) => {{ + let mut builder = $builder; + for raw_bytes in $raw { + match raw_bytes { + None => builder.append_null(), + Some(raw_vector) => { + let mut offset = 0; + while offset < raw_vector.len() { + let len = i64::from_ne_bytes( + raw_vector[offset..offset + 8] + .try_into() + .expect("slice of length 8"), + ); + offset += 8; + if len == -1 { + builder.values().append_null(); + } else { + let s = unsafe { + std::str::from_utf8_unchecked( + &raw_vector[offset..offset + len as usize], + ) + }; + builder.values().append_value(s); + offset += len as usize; + } + } + builder.append(true); + } + } + } + Ok(Arc::new(builder.finish()) as ArrayRef) + }}; +} +macro_rules! decode_scalar_string { + ($raw:expr, $builder:expr) => {{ + let mut builder = $builder; + for raw_bytes in $raw { + match raw_bytes { + Some(raw_vector) => { + let s = unsafe { std::str::from_utf8_unchecked(raw_vector) }; + builder.append_value(s); + } + None => builder.append_null(), + } + } + Ok(Arc::new(builder.finish()) as ArrayRef) + }}; +} +/// Entry stored inside `unique_dict_value_mapping`. Caching `hash` on the entry +struct DictEntry { + hash: u64, + group_id: usize, + bytes: Vec<u8>, +} + +pub struct GroupValuesDictionary<K: ArrowDictionaryKeyType + Send> { + // stores the order new unique elements are seen for self.emit() + seen_elements: Vec<Option<Vec<u8>>>, + value_dt: DataType, + _phantom: PhantomData<K>, + // keeps track of which values weve already seen, keyed by raw value hash. + unique_dict_value_mapping: HashTable<DictEntry>, + + random_state: RandomState, + + // cache the group id for nulls since they all map to the same group + null_group_id: Option<usize>, + intern_called: bool, + // 0. cache pointer of arrays, this avoids having to re-compute hashing for arrays weve already seen on past iterations + // 1. avoid re-allocating buffer inbetween calls, instead of allocating a new vector each time re-use inbetween calls + values_cache: (Option<ArrayRef>, Vec<u64>), +} + +impl<K: ArrowDictionaryKeyType + Send> GroupValuesDictionary<K> { + pub fn new(data_type: &DataType) -> Self { + Self { + seen_elements: Vec::new(), + unique_dict_value_mapping: HashTable::with_capacity(INITIAL_PRE_ALLOCATION), + value_dt: data_type.clone(), + _phantom: PhantomData, + random_state: RandomState::with_seed(0), + null_group_id: None, + intern_called: false, + values_cache: (None, Vec::new()), + } + } + + /// Returns the existing `group_id` for the value with this hash and bytes, + /// or inserts a new entry and returns the freshly assigned group_id. + fn lookup_or_insert_in_table(&mut self, hash: u64, raw: &[u8]) -> usize { + match self + .unique_dict_value_mapping + .entry(hash, |e| e.bytes == raw, |e| e.hash) + { + HashTableEntry::Occupied(o) => o.get().group_id, + HashTableEntry::Vacant(v) => { + let new_group_id = self.seen_elements.len(); + self.seen_elements.push(Some(raw.to_vec())); // replace this with raw buffer to avoid this double copy #TODO see https://github.com/apache/datafusion/issues/22078 + v.insert(DictEntry { + hash, + group_id: new_group_id, + bytes: raw.to_vec(), + }); + new_group_id + } + } + } + fn compute_value_hashes(&mut self, values: &ArrayRef) -> Result<()> { + self.values_cache.1.clear(); + self.values_cache.1.resize(values.len(), 0); + create_hashes( + [Arc::clone(values)], + &self.random_state, + &mut self.values_cache.1, + )?; + Ok(()) + //Ok(hashes) + } + + fn get_raw_bytes(values: &ArrayRef, index: usize) -> Cow<'_, [u8]> { + match values.data_type() { + DataType::Utf8 => Cow::Borrowed( + values + .as_any() + .downcast_ref::<StringArray>() + .expect("Expected StringArray") + .value(index) + .as_bytes(), + ), + DataType::LargeUtf8 => Cow::Borrowed( + values + .as_any() + .downcast_ref::<LargeStringArray>() + .expect("Expected LargeStringArray") + .value(index) + .as_bytes(), + ), + DataType::Utf8View => Cow::Borrowed( + values + .as_any() + .downcast_ref::<StringViewArray>() + .expect("Expected StringViewArray") + .value(index) + .as_bytes(), + ), + DataType::List(_) => { + let list_array = values + .as_any() + .downcast_ref::<ListArray>() + .expect("Expected ListArray"); + + debug_assert!(!list_array.is_null(index)); + + let start = list_array.value_offsets()[index] as usize; + let end = list_array.value_offsets()[index + 1] as usize; + let child = list_array.values(); + + let mut bytes = Vec::new(); + for i in start..end { + if child.is_null(i) { + // acts as a marker for transform_into_array to write a null + bytes.extend_from_slice(&(-1i64).to_ne_bytes()); + } else { + let raw = Self::get_raw_bytes(child, i); + bytes.extend_from_slice(&(raw.len() as i64).to_ne_bytes()); + bytes.extend_from_slice(&raw); + } + } + Cow::Owned(bytes) + } + other => unimplemented!("get_raw_bytes not implemented for {other:?}"), + } + } + + #[inline] + fn get_null_group_id(&mut self) -> usize { + if let Some(group_id) = self.null_group_id { + group_id + } else { + let new_group_id = self.seen_elements.len(); + self.seen_elements.push(None); + self.null_group_id = Some(new_group_id); + new_group_id + } + } + fn transform_into_array(&self, raw: &[Option<Vec<u8>>]) -> Result<ArrayRef> { + let item_capacity = raw.len(); + let data_capacity = item_capacity * AVG_BYTES_PER_DICT_VALUE; + match &self.value_dt { + DataType::Utf8 => decode_scalar_string!( + raw, + StringBuilder::with_capacity(item_capacity, data_capacity) + ), + DataType::LargeUtf8 => decode_scalar_string!( + raw, + LargeStringBuilder::with_capacity(item_capacity, data_capacity) + ), + DataType::Utf8View => decode_scalar_string!( + raw, + StringViewBuilder::with_capacity(item_capacity) + ), + DataType::List(field) => match field.data_type() { + DataType::Utf8 => decode_list!( + raw, + ListBuilder::with_capacity( + StringBuilder::with_capacity(item_capacity, data_capacity), + item_capacity, + ) + ), + DataType::LargeUtf8 => decode_list!( + raw, + ListBuilder::with_capacity( + LargeStringBuilder::with_capacity(item_capacity, data_capacity), + item_capacity, + ) + ), + DataType::Utf8View => decode_list!( + raw, + ListBuilder::with_capacity( + StringViewBuilder::with_capacity(item_capacity), + item_capacity, + ) + ), + other => Err(NotImplemented(format!( + "transform_into_array not implemented for List<{other:?}>" + ))), + }, + other => Err(NotImplemented(format!( + "transform_into_array not implemented for {other:?}" + ))), + } + } + #[inline] + fn keys_to_usize(key_array: &PrimitiveArray<K>) -> Vec<Option<usize>> { + (0..key_array.len()) + .map(|i| { + if key_array.is_null(i) { + None + } else { + Some(key_array.value(i).to_usize().unwrap()) + } + }) + .collect() + } +} + +impl<K: ArrowDictionaryKeyType + Send> GroupValues for GroupValuesDictionary<K> { + fn size(&self) -> usize { + let seen_elements_size = self.seen_elements.capacity() + * size_of::<Option<Vec<u8>>>() + + self + .seen_elements + .iter() + .filter_map(|opt| opt.as_ref()) + .map(|inner| inner.capacity()) + .sum::<usize>(); + + let unique_mapping_size = self.unique_dict_value_mapping.capacity() + * size_of::<DictEntry>() + + self + .unique_dict_value_mapping + .iter() + .map(|e| e.bytes.capacity()) + .sum::<usize>(); + + let values_cache_size = self.values_cache.1.capacity() * size_of::<u64>() + + self + .values_cache + .0 + .as_ref() + .map(|a| a.get_array_memory_size()) + .unwrap_or(0); + + size_of::<Self>() + seen_elements_size + unique_mapping_size + values_cache_size + } + fn len(&self) -> usize { + self.seen_elements.len() + } + fn is_empty(&self) -> bool { + self.seen_elements.is_empty() + } + fn intern(&mut self, cols: &[ArrayRef], groups: &mut Vec<usize>) -> Result<()> { + assert_eq!( + cols.len(), + 1, + "GroupValuesDictionary only supports a single column" + ); + let array = Arc::clone(&cols[0]); + groups.clear(); // zero out buffer + let dict_array = array + .as_any() + .downcast_ref::<DictionaryArray<K>>() + .ok_or_else(|| { + Internal(format!( + "GroupValuesDictionary expected DictionaryArray but got {:?}", + array.data_type() + )) + })?; + + let values = dict_array.values(); + let key_array = dict_array.keys(); + if key_array.is_empty() { + return Ok(()); + } + let keys_as_usize: Vec<Option<usize>> = Self::keys_to_usize(key_array); + + let cache_hit = self + .values_cache + .0 + .as_ref() + .map(|cached| Arc::ptr_eq(cached, values)) + .unwrap_or(false); + + if !cache_hit { + // first time seeing this values array to compute hashes, and cache the pointer, cheap operation + self.compute_value_hashes(values)?; + self.values_cache.0 = Some(Arc::clone(values)); + } + let mut key_to_group: Vec<Option<usize>> = vec![None; values.len()]; + if self.intern_called { Review Comment: I think that makes sense. just to be safe ill benchmark the difference & share the results if performance doesn't improve like we expect it to. -- This is an automated message from the Apache Git Service. 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