feat(parquet): add struct-column writer benchmarks

Add three new benchmark cases to the arrow_writer benchmark suite for
evaluating write performance on struct columns at varying null
densities:

- `struct_non_null`: a nullable struct with 0% null rows and
  non-nullable primitive children;
- `struct_sparse_99pct_null`: a nullable struct with 99% null rows,
  exercising null batching through one level of struct nesting;
- `struct_all_null`: a nullable struct with 100% null rows, exercising
  the uniform-null path through struct nesting.

  Baseline results (Apple M1 Max):

  struct_non_null/default              29.9 ms
  struct_non_null/parquet_2            38.2 ms
  struct_non_null/zstd_parquet_2       50.9 ms
  struct_sparse_99pct_null/default      7.2 ms
  struct_sparse_99pct_null/parquet_2    7.3 ms
  struct_sparse_99pct_null/zstd_p2      8.1 ms
  struct_all_null/default              83.3 µs
  struct_all_null/parquet_2            82.5 µs
  struct_all_null/zstd_parquet_2      106.6 µs

Signed-off-by: Hippolyte Barraud <hippolyte.barraud@datadoghq.com>

Author: HippoBaro

parquet/benches/arrow_writer.rs

@@ -266,6 +266,25 @@ fn create_list_primitive_bench_batch_non_null(
     )?)
 }
 
+fn create_struct_bench_batch(size: usize, null_density: f32) -> Result<RecordBatch> {
+    let fields = vec![Field::new(
+        "_1",
+        DataType::Struct(Fields::from(vec![
+            Field::new("_1", DataType::Int32, false),
+            Field::new("_2", DataType::Int64, false),
+            Field::new("_3", DataType::Float32, false),
+        ])),
+        true,
+    )];
+    let schema = Schema::new(fields);
+    Ok(create_random_batch(
+        Arc::new(schema),
+        size,
+        null_density,
+        0.75,
+    )?)
+}
+
 fn _create_nested_bench_batch(
     size: usize,
     null_density: f32,
@@ -400,6 +419,15 @@ fn create_batches() -> Vec<(&'static str, RecordBatch)> {
     let batch = create_primitive_bench_batch(BATCH_SIZE, 1.0, 0.75).unwrap();
     batches.push(("primitive_all_null", batch));
 
+    let batch = create_struct_bench_batch(BATCH_SIZE, 0.0).unwrap();
+    batches.push(("struct_non_null", batch));
+
+    let batch = create_struct_bench_batch(BATCH_SIZE, 0.99).unwrap();
+    batches.push(("struct_sparse_99pct_null", batch));
+
+    let batch = create_struct_bench_batch(BATCH_SIZE, 1.0).unwrap();
+    batches.push(("struct_all_null", batch));
+
     batches
 }