Faster StringDictionaryBuilder (~60% faster) (#1851)

arrow/Cargo.toml

@@ -38,13 +38,15 @@ path = "src/lib.rs"
 bench = false
 
 [dependencies]
+ahash = { version = "0.7", default-features = false }
 serde = { version = "1.0", default-features = false }
 serde_derive = { version = "1.0", default-features = false }
 serde_json = { version = "1.0", default-features = false, features = ["preserve_order"] }
 indexmap = { version = "1.9", default-features = false, features = ["std"] }
 rand = { version = "0.8", default-features = false, features =  ["std", "std_rng"], optional = true }
 num = { version = "0.4", default-features = false, features = ["std"] }
 half = { version = "2.0", default-features = false }
+hashbrown = { version = "0.12", default-features = false }
 csv_crate = { version = "1.1", default-features = false, optional = true, package="csv" }
 regex = { version = "1.5.6", default-features = false, features = ["std", "unicode"] }
 lazy_static = { version = "1.4", default-features = false }

arrow/benches/string_dictionary_builder.rs

@@ -0,0 +1,70 @@
+// 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::{Int32Builder, StringBuilder, StringDictionaryBuilder};
+use criterion::{criterion_group, criterion_main, Criterion};
+use rand::{thread_rng, Rng};
+
+/// Note: this is best effort, not all keys are necessarily present or unique
+fn build_strings(dict_size: usize, total_size: usize, key_len: usize) -> Vec<String> {
+    let mut rng = thread_rng();
+    let values: Vec<String> = (0..dict_size)
+        .map(|_| (0..key_len).map(|_| rng.gen::<char>()).collect())
+        .collect();
+
+    (0..total_size)
+        .map(|_| values[rng.gen_range(0..dict_size)].clone())
+        .collect()
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let mut group = c.benchmark_group("string_dictionary_builder");
+
+    let mut do_bench = |dict_size: usize, total_size: usize, key_len: usize| {
+        group.bench_function(
+            format!(
+                "(dict_size:{}, len:{}, key_len: {})",
+                dict_size, total_size, key_len
+            ),
+            |b| {
+                let strings = build_strings(dict_size, total_size, key_len);
+                b.iter(|| {
+                    let keys = Int32Builder::new(strings.len());
+                    let values = StringBuilder::new((key_len + 1) * dict_size);
+                    let mut builder = StringDictionaryBuilder::new(keys, values);
+
+                    for val in &strings {
+                        builder.append(val).unwrap();
+                    }
+
+                    builder.finish();
+                })
+            },
+        );
+    };
+
+    do_bench(20, 1000, 5);
+    do_bench(100, 1000, 5);
+    do_bench(100, 1000, 10);
+    do_bench(100, 10000, 10);
+    do_bench(100, 10000, 100);
+
+    group.finish();
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

arrow/src/array/builder/generic_list_builder.rs

@@ -107,6 +107,11 @@ where
         &mut self.values_builder
     }
 
+    /// Returns the child array builder as an immutable reference
+    pub fn values_ref(&self) -> &T {
+        &self.values_builder
+    }
+
     /// Finish the current variable-length list array slot
     #[inline]
     pub fn append(&mut self, is_valid: bool) -> Result<()> {
@@ -152,6 +157,11 @@ where
 
         GenericListArray::<OffsetSize>::from(array_data)
     }
+
+    /// Returns the current offsets buffer as a slice
+    pub fn offsets_slice(&self) -> &[OffsetSize] {
+        self.offsets_builder.as_slice()
+    }
 }
 
 #[cfg(test)]

arrow/src/array/builder/generic_string_builder.rs

@@ -87,6 +87,16 @@ impl<OffsetSize: OffsetSizeTrait> GenericStringBuilder<OffsetSize> {
     pub fn finish(&mut self) -> GenericStringArray<OffsetSize> {
         GenericStringArray::<OffsetSize>::from(self.builder.finish())
     }
+
+    /// Returns the current values buffer as a slice
+    pub fn values_slice(&self) -> &[u8] {
+        self.builder.values_ref().values_slice()
+    }
+
+    /// Returns the current offsets buffer as a slice
+    pub fn offsets_slice(&self) -> &[OffsetSize] {
+        self.builder.offsets_slice()
+    }
 }
 
 impl<OffsetSize: OffsetSizeTrait> ArrayBuilder for GenericStringBuilder<OffsetSize> {

arrow/src/array/builder/primitive_builder.rs

@@ -230,6 +230,11 @@ impl<T: ArrowPrimitiveType> PrimitiveBuilder<T> {
         b.append_n(self.values_builder.len(), true);
         self.bitmap_builder = Some(b);
     }
+
+    /// Returns the current values buffer as a slice
+    pub fn values_slice(&self) -> &[T::Native] {
+        self.values_builder.as_slice()
+    }
 }
 
 #[cfg(test)]

arrow/src/array/builder/string_dictionary_builder.rs

@@ -15,21 +15,17 @@
 // specific language governing permissions and limitations
 // under the License.
 
+use super::PrimitiveBuilder;
+use crate::array::{
+    Array, ArrayBuilder, ArrayRef, DictionaryArray, StringArray, StringBuilder,
+};
+use crate::datatypes::{ArrowDictionaryKeyType, ArrowNativeType};
+use crate::error::{ArrowError, Result};
+use hashbrown::hash_map::RawEntryMut;
+use hashbrown::HashMap;
 use std::any::Any;
-use std::collections::HashMap;
 use std::sync::Arc;
 
-use crate::array::array::Array;
-use crate::array::ArrayBuilder;
-use crate::array::ArrayRef;
-use crate::array::ArrowDictionaryKeyType;
-use crate::array::DictionaryArray;
-use crate::array::PrimitiveBuilder;
-use crate::array::StringArray;
-use crate::array::StringBuilder;
-use crate::datatypes::ArrowNativeType;
-use crate::error::{ArrowError, Result};
-
 /// Array builder for `DictionaryArray` that stores Strings. For example to map a set of byte indices
 /// to String values. Note that the use of a `HashMap` here will not scale to very large
 /// arrays or result in an ordered dictionary.
@@ -76,9 +72,16 @@ pub struct StringDictionaryBuilder<K>
 where
     K: ArrowDictionaryKeyType,
 {
+    state: ahash::RandomState,
+    /// Used to provide a lookup from string value to key type
+    ///
+    /// Note: K's hash implementation is not used, instead the raw entry
+    /// API is used to store keys w.r.t the hash of the strings themselves
+    ///
+    dedup: HashMap<K::Native, (), ()>,
+
     keys_builder: PrimitiveBuilder<K>,
     values_builder: StringBuilder,
-    map: HashMap<Box<[u8]>, K::Native>,
 }
 
 impl<K> StringDictionaryBuilder<K>
@@ -88,9 +91,10 @@ where
     /// Creates a new `StringDictionaryBuilder` from a keys builder and a value builder.
     pub fn new(keys_builder: PrimitiveBuilder<K>, values_builder: StringBuilder) -> Self {
         Self {
+            state: Default::default(),
+            dedup: HashMap::with_capacity_and_hasher(keys_builder.capacity(), ()),
             keys_builder,
             values_builder,
-            map: HashMap::new(),
         }
     }
 
@@ -122,27 +126,44 @@ where
         keys_builder: PrimitiveBuilder<K>,
         dictionary_values: &StringArray,
     ) -> Result<Self> {
+        let state = ahash::RandomState::default();
         let dict_len = dictionary_values.len();
-        let mut values_builder =
-            StringBuilder::with_capacity(dict_len, dictionary_values.value_data().len());
-        let mut map: HashMap<Box<[u8]>, K::Native> = HashMap::with_capacity(dict_len);
-        for i in 0..dict_len {
-            if dictionary_values.is_valid(i) {
-                let value = dictionary_values.value(i);
-                map.insert(
-                    value.as_bytes().into(),
-                    K::Native::from_usize(i)
-                        .ok_or(ArrowError::DictionaryKeyOverflowError)?,
-                );
-                values_builder.append_value(value)?;
-            } else {
-                values_builder.append_null()?;
+
+        let mut dedup = HashMap::with_capacity_and_hasher(dict_len, ());
+
+        let values_len = dictionary_values.value_data().len();
+        let mut values_builder = StringBuilder::with_capacity(dict_len, values_len);
+
+        for (idx, maybe_value) in dictionary_values.iter().enumerate() {
+            match maybe_value {
+                Some(value) => {
+                    let hash = compute_hash(&state, value.as_bytes());
+
+                    let key = K::Native::from_usize(idx)
+                        .ok_or(ArrowError::DictionaryKeyOverflowError)?;
+
+                    let entry =
+                        dedup.raw_entry_mut().from_hash(hash, |key: &K::Native| {
+                            value.as_bytes() == get_bytes(&values_builder, key)
+                        });
+
+                    if let RawEntryMut::Vacant(v) = entry {
+                        v.insert_with_hasher(hash, key, (), |key| {
+                            compute_hash(&state, get_bytes(&values_builder, key))
+                        });
+                    }
+
+                    values_builder.append_value(value)?;
+                }
+                None => values_builder.append_null()?,
             }
         }
+
         Ok(Self {
+            state,
+            dedup,
             keys_builder,
             values_builder,
-            map,
         })
     }
 }
@@ -190,19 +211,35 @@ where
     /// if already present in the values array or a new index if the
     /// value is appended to the values array.
     pub fn append(&mut self, value: impl AsRef<str>) -> Result<K::Native> {
-        if let Some(&key) = self.map.get(value.as_ref().as_bytes()) {
-            // Append existing value.
-            self.keys_builder.append_value(key)?;
-            Ok(key)
-        } else {
-            // Append new value.
-            let key = K::Native::from_usize(self.values_builder.len())
-                .ok_or(ArrowError::DictionaryKeyOverflowError)?;
-            self.values_builder.append_value(value.as_ref())?;
-            self.keys_builder.append_value(key as K::Native)?;
-            self.map.insert(value.as_ref().as_bytes().into(), key);
-            Ok(key)
-        }
+        let value = value.as_ref();
+
+        let state = &self.state;
+        let storage = &mut self.values_builder;
+        let hash = compute_hash(state, value.as_bytes());
+
+        let entry = self
+            .dedup
+            .raw_entry_mut()
+            .from_hash(hash, |key| value.as_bytes() == get_bytes(storage, key));
+
+        let key = match entry {
+            RawEntryMut::Occupied(entry) => *entry.into_key(),
+            RawEntryMut::Vacant(entry) => {
+                let index = storage.len();
+                storage.append_value(value)?;
+                let key = K::Native::from_usize(index)
+                    .ok_or(ArrowError::DictionaryKeyOverflowError)?;
+
+                *entry
+                    .insert_with_hasher(hash, key, (), |key| {
+                        compute_hash(state, get_bytes(storage, key))
+                    })
+                    .0
+            }
+        };
+        self.keys_builder.append_value(key)?;
+
+        Ok(key)
     }
 
     #[inline]
@@ -212,12 +249,30 @@ where
 
     /// Builds the `DictionaryArray` and reset this builder.
     pub fn finish(&mut self) -> DictionaryArray<K> {
-        self.map.clear();
+        self.dedup.clear();
         let value_ref: ArrayRef = Arc::new(self.values_builder.finish());
         self.keys_builder.finish_dict(value_ref)
     }
 }
 
+fn compute_hash(hasher: &ahash::RandomState, value: &[u8]) -> u64 {
+    use std::hash::{BuildHasher, Hash, Hasher};
+    let mut state = hasher.build_hasher();
+    value.hash(&mut state);
+    state.finish()
+}
+
+fn get_bytes<'a, K: ArrowNativeType>(values: &'a StringBuilder, key: &K) -> &'a [u8] {
+    let offsets = values.offsets_slice();
+    let values = values.values_slice();
+
+    let idx = key.to_usize().unwrap();
+    let end_offset = offsets[idx + 1].to_usize().unwrap();
+    let start_offset = offsets[idx].to_usize().unwrap();
+
+    &values[start_offset..end_offset]
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;