feat: Reduce allocations for aggregating Statistics (#20768)

## Which issue does this PR close?

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- Closes #15809.

## Rationale for this change

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## What changes are included in this PR?
Vectorize aggregations for combining statistics by gathering all values
then calling kernels once
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## Are these changes tested?
Unit tests + existing tests
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## Are there any user-facing changes?
Removed `merge_iter`

Author: jonathanc-n

datafusion/common/Cargo.toml

@@ -61,6 +61,10 @@ name = "with_hashes"
 harness = false
 name = "scalar_to_array"
 
+[[bench]]
+harness = false
+name = "stats_merge"
+
 [dependencies]
 ahash = { workspace = true }
 apache-avro = { workspace = true, features = [

datafusion/common/benches/stats_merge.rs

@@ -0,0 +1,85 @@
+// 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.
+
+//! Benchmark for `Statistics::try_merge_iter`.
+
+use std::sync::Arc;
+
+use arrow::datatypes::{DataType, Field, Schema};
+use criterion::{BenchmarkId, Criterion, criterion_group, criterion_main};
+use datafusion_common::stats::Precision;
+use datafusion_common::{ColumnStatistics, ScalarValue, Statistics};
+
+/// Build a vector of `n` with `num_cols` columns
+fn make_stats(n: usize, num_cols: usize) -> Vec<Statistics> {
+    (0..n)
+        .map(|i| {
+            let mut stats = Statistics::default()
+                .with_num_rows(Precision::Exact(100 + i))
+                .with_total_byte_size(Precision::Exact(8000 + i * 80));
+            for c in 0..num_cols {
+                let base = (i * num_cols + c) as i64;
+                stats = stats.add_column_statistics(
+                    ColumnStatistics::new_unknown()
+                        .with_null_count(Precision::Exact(i))
+                        .with_min_value(Precision::Exact(ScalarValue::Int64(Some(base))))
+                        .with_max_value(Precision::Exact(ScalarValue::Int64(Some(
+                            base + 1000,
+                        ))))
+                        .with_sum_value(Precision::Exact(ScalarValue::Int64(Some(
+                            base * 100,
+                        )))),
+                );
+            }
+            stats
+        })
+        .collect()
+}
+
+fn bench_stats_merge(c: &mut Criterion) {
+    let mut group = c.benchmark_group("stats_merge");
+
+    for &num_partitions in &[10, 100, 500] {
+        for &num_cols in &[1, 5, 20] {
+            let items = make_stats(num_partitions, num_cols);
+            let schema = Arc::new(Schema::new(
+                (0..num_cols)
+                    .map(|i| Field::new(format!("col{i}"), DataType::Int64, true))
+                    .collect::<Vec<_>>(),
+            ));
+
+            let param = format!("{num_partitions}parts_{num_cols}cols");
+
+            group.bench_with_input(
+                BenchmarkId::new("try_merge_iter", &param),
+                &(&items, &schema),
+                |b, (items, schema)| {
+                    b.iter(|| {
+                        std::hint::black_box(
+                            Statistics::try_merge_iter(*items, schema).unwrap(),
+                        );
+                    });
+                },
+            );
+        }
+    }
+
+    group.finish();
+}
+
+criterion_group!(benches, bench_stats_merge);
+criterion_main!(benches);