feat: Optimize hash util for MapArray (#20179)

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- Closes #20151 .

## Rationale for this change
Reduce the irrelevant data being used to hash for `MapArray`
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Author: jonathanc-n

datafusion/common/benches/with_hashes.rs

@@ -19,13 +19,13 @@
 
 use ahash::RandomState;
 use arrow::array::{
-    Array, ArrayRef, ArrowPrimitiveType, DictionaryArray, GenericStringArray,
-    NullBufferBuilder, OffsetSizeTrait, PrimitiveArray, RunArray, StringViewArray,
-    StructArray, make_array,
+    Array, ArrayRef, ArrowPrimitiveType, DictionaryArray, GenericStringArray, Int32Array,
+    Int64Array, ListArray, MapArray, NullBufferBuilder, OffsetSizeTrait, PrimitiveArray,
+    RunArray, StringViewArray, StructArray, UnionArray, make_array,
 };
-use arrow::buffer::NullBuffer;
+use arrow::buffer::{NullBuffer, OffsetBuffer, ScalarBuffer};
 use arrow::datatypes::{
-    ArrowDictionaryKeyType, DataType, Field, Fields, Int32Type, Int64Type,
+    ArrowDictionaryKeyType, DataType, Field, Fields, Int32Type, Int64Type, UnionFields,
 };
 use criterion::{Bencher, Criterion, criterion_group, criterion_main};
 use datafusion_common::hash_utils::with_hashes;
@@ -40,6 +40,7 @@ const BATCH_SIZE: usize = 8192;
 struct BenchData {
     name: &'static str,
     array: ArrayRef,
+    /// Union arrays can't have null bitmasks added
     supports_nulls: bool,
 }
 
@@ -78,6 +79,26 @@ fn criterion_benchmark(c: &mut Criterion) {
             array: pool.dictionary_array::<Int32Type>(BATCH_SIZE),
             supports_nulls: true,
         },
+        BenchData {
+            name: "list_array",
+            array: list_array(BATCH_SIZE),
+            supports_nulls: true,
+        },
+        BenchData {
+            name: "map_array",
+            array: map_array(BATCH_SIZE),
+            supports_nulls: true,
+        },
+        BenchData {
+            name: "sparse_union",
+            array: sparse_union_array(BATCH_SIZE),
+            supports_nulls: false,
+        },
+        BenchData {
+            name: "dense_union",
+            array: dense_union_array(BATCH_SIZE),
+            supports_nulls: false,
+        },
         BenchData {
             name: "struct_array",
             array: create_struct_array(&pool, BATCH_SIZE),
@@ -103,10 +124,9 @@ fn criterion_benchmark(c: &mut Criterion) {
             let arrays = vec![array.clone(), array.clone(), array.clone()];
             do_hash_test(b, &arrays);
         });
-
+        // Union arrays can't have null bitmasks
         if supports_nulls {
             let nullable_array = add_nulls(&array);
-
             c.bench_function(&format!("{name}: single, nulls"), |b| {
                 do_hash_test(b, std::slice::from_ref(&nullable_array));
             });
@@ -268,6 +288,222 @@ where
     Arc::new(array)
 }
 
+/// Benchmark sliced arrays to demonstrate the optimization for when an array is
+/// sliced, the underlying buffer may be much larger than what's referenced by
+/// the slice. The optimization avoids hashing unreferenced elements.
+fn sliced_array_benchmark(c: &mut Criterion) {
+    // Test with different slice ratios: slice_size / total_size
+    // Smaller ratio = more potential savings from the optimization
+    let slice_ratios = [10, 5, 2]; // 1/10, 1/5, 1/2 of total
+
+    for ratio in slice_ratios {
+        let total_rows = BATCH_SIZE * ratio;
+        let slice_offset = BATCH_SIZE * (ratio / 2); // Take from middle
+        let slice_len = BATCH_SIZE;
+
+        // Sliced ListArray
+        {
+            let full_array = list_array(total_rows);
+            let sliced: ArrayRef = Arc::new(
+                full_array
+                    .as_any()
+                    .downcast_ref::<ListArray>()
+                    .unwrap()
+                    .slice(slice_offset, slice_len),
+            );
+            c.bench_function(
+                &format!("list_array_sliced: 1/{ratio} of {total_rows} rows"),
+                |b| {
+                    do_hash_test_with_len(b, std::slice::from_ref(&sliced), slice_len);
+                },
+            );
+        }
+
+        // Sliced MapArray
+        {
+            let full_array = map_array(total_rows);
+            let sliced: ArrayRef = Arc::new(
+                full_array
+                    .as_any()
+                    .downcast_ref::<MapArray>()
+                    .unwrap()
+                    .slice(slice_offset, slice_len),
+            );
+            c.bench_function(
+                &format!("map_array_sliced: 1/{ratio} of {total_rows} rows"),
+                |b| {
+                    do_hash_test_with_len(b, std::slice::from_ref(&sliced), slice_len);
+                },
+            );
+        }
+
+        // Sliced Sparse UnionArray
+        {
+            let full_array = sparse_union_array(total_rows);
+            let sliced: ArrayRef = Arc::new(
+                full_array
+                    .as_any()
+                    .downcast_ref::<UnionArray>()
+                    .unwrap()
+                    .slice(slice_offset, slice_len),
+            );
+            c.bench_function(
+                &format!("sparse_union_sliced: 1/{ratio} of {total_rows} rows"),
+                |b| {
+                    do_hash_test_with_len(b, std::slice::from_ref(&sliced), slice_len);
+                },
+            );
+        }
+    }
+}
+
+fn do_hash_test_with_len(b: &mut Bencher, arrays: &[ArrayRef], expected_len: usize) {
+    let state = RandomState::new();
+    b.iter(|| {
+        with_hashes(arrays, &state, |hashes| {
+            assert_eq!(hashes.len(), expected_len);
+            Ok(())
+        })
+        .unwrap();
+    });
+}
+
+fn list_array(num_rows: usize) -> ArrayRef {
+    let mut rng = make_rng();
+    let elements_per_row = 5;
+    let total_elements = num_rows * elements_per_row;
+
+    let values: Int64Array = (0..total_elements)
+        .map(|_| Some(rng.random::<i64>()))
+        .collect();
+    let offsets: Vec<i32> = (0..=num_rows)
+        .map(|i| (i * elements_per_row) as i32)
+        .collect();
+
+    Arc::new(ListArray::new(
+        Arc::new(Field::new("item", DataType::Int64, true)),
+        OffsetBuffer::new(ScalarBuffer::from(offsets)),
+        Arc::new(values),
+        None,
+    ))
+}
+
+fn map_array(num_rows: usize) -> ArrayRef {
+    let mut rng = make_rng();
+    let entries_per_row = 5;
+    let total_entries = num_rows * entries_per_row;
+
+    let keys: Int32Array = (0..total_entries)
+        .map(|_| Some(rng.random::<i32>()))
+        .collect();
+    let values: Int64Array = (0..total_entries)
+        .map(|_| Some(rng.random::<i64>()))
+        .collect();
+    let offsets: Vec<i32> = (0..=num_rows)
+        .map(|i| (i * entries_per_row) as i32)
+        .collect();
+
+    let entries = StructArray::try_new(
+        Fields::from(vec![
+            Field::new("keys", DataType::Int32, false),
+            Field::new("values", DataType::Int64, true),
+        ]),
+        vec![Arc::new(keys), Arc::new(values)],
+        None,
+    )
+    .unwrap();
+
+    Arc::new(MapArray::new(
+        Arc::new(Field::new(
+            "entries",
+            DataType::Struct(Fields::from(vec![
+                Field::new("keys", DataType::Int32, false),
+                Field::new("values", DataType::Int64, true),
+            ])),
+            false,
+        )),
+        OffsetBuffer::new(ScalarBuffer::from(offsets)),
+        entries,
+        None,
+        false,
+    ))
+}
+
+fn sparse_union_array(num_rows: usize) -> ArrayRef {
+    let mut rng = make_rng();
+    let num_types = 5;
+
+    let type_ids: Vec<i8> = (0..num_rows)
+        .map(|_| rng.random_range(0..num_types) as i8)
+        .collect();
+    let (fields, children): (Vec<_>, Vec<_>) = (0..num_types)
+        .map(|i| {
+            (
+                (
+                    i as i8,
+                    Arc::new(Field::new(format!("f{i}"), DataType::Int64, true)),
+                ),
+                primitive_array::<Int64Type>(num_rows),
+            )
+        })
+        .unzip();
+
+    Arc::new(
+        UnionArray::try_new(
+            UnionFields::from_iter(fields),
+            ScalarBuffer::from(type_ids),
+            None,
+            children,
+        )
+        .unwrap(),
+    )
+}
+
+fn dense_union_array(num_rows: usize) -> ArrayRef {
+    let mut rng = make_rng();
+    let num_types = 5;
+    let type_ids: Vec<i8> = (0..num_rows)
+        .map(|_| rng.random_range(0..num_types) as i8)
+        .collect();
+
+    let mut type_counts = vec![0i32; num_types];
+    for &tid in &type_ids {
+        type_counts[tid as usize] += 1;
+    }
+
+    let mut current_offsets = vec![0i32; num_types];
+    let offsets: Vec<i32> = type_ids
+        .iter()
+        .map(|&tid| {
+            let offset = current_offsets[tid as usize];
+            current_offsets[tid as usize] += 1;
+            offset
+        })
+        .collect();
+
+    let (fields, children): (Vec<_>, Vec<_>) = (0..num_types)
+        .map(|i| {
+            (
+                (
+                    i as i8,
+                    Arc::new(Field::new(format!("f{i}"), DataType::Int64, true)),
+                ),
+                primitive_array::<Int64Type>(type_counts[i] as usize),
+            )
+        })
+        .unzip();
+
+    Arc::new(
+        UnionArray::try_new(
+            UnionFields::from_iter(fields),
+            ScalarBuffer::from(type_ids),
+            Some(ScalarBuffer::from(offsets)),
+            children,
+        )
+        .unwrap(),
+    )
+}
+
 fn boolean_array(array_len: usize) -> ArrayRef {
     let mut rng = make_rng();
     Arc::new(
@@ -329,5 +565,5 @@ where
     )
 }
 
-criterion_group!(benches, criterion_benchmark);
+criterion_group!(benches, criterion_benchmark, sliced_array_benchmark);
 criterion_main!(benches);