[Json] Add json reader benchmarks for Map and REE (#9616)

# Which issue does this PR close?

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- Relates to #9497.

# Rationale for this change

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# What changes are included in this PR?

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PR.
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As part of the effort to move the Json reader away from `ArrayData`
toward typed `ArrayRef` APIs, it's necessary to change the
`ArrayDecoder::decode` interface to return `ArrayRef` directly and
updates all decoder implementations (list, struct, map, run-end encoded)
to construct typed arrays without intermediate `ArrayData` round-trips.
New benchmarks for map and run-end encoded decoding are added to verify
there is no performance regression.

# Are these changes tested?

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Yes

# Are there any user-facing changes?

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No

Author: liamzwbao

arrow-json/benches/json_reader.rs

@@ -28,14 +28,28 @@ use std::fmt::Write;
 use std::hint::black_box;
 use std::sync::Arc;
 
+// Shared
 const ROWS: usize = 1 << 17; // 128K rows
 const BATCH_SIZE: usize = 1 << 13; // 8K rows per batch
 
+// Wide object / struct
 const WIDE_FIELDS: usize = 64;
-const BINARY_BYTES: usize = 64;
 const WIDE_PROJECTION_TOTAL_FIELDS: usize = 100; // 100 fields total, select only 3
-const LIST_SHORT_ELEMENTS: usize = 5;
-const LIST_LONG_ELEMENTS: usize = 100;
+
+// Binary
+const BINARY_BYTES: usize = 64;
+
+// List
+const SHORT_LIST_ELEMENTS: usize = 5;
+const LONG_LIST_ELEMENTS: usize = 100;
+
+// Map
+const SMALL_MAP_ENTRIES: usize = 5;
+const LARGE_MAP_ENTRIES: usize = 50;
+
+// Run-end encoded
+const SHORT_REE_RUN_LENGTH: usize = 2;
+const LONG_REE_RUN_LENGTH: usize = 100;
 
 fn decode_and_flush(decoder: &mut Decoder, data: &[u8]) {
     let mut offset = 0;
@@ -289,19 +303,174 @@ fn bench_decode_list(c: &mut Criterion) {
     let schema = build_list_schema();
 
     // Short lists: tests list handling overhead (few elements per row)
-    let short_data = build_list_json(ROWS, LIST_SHORT_ELEMENTS);
-    bench_decode_schema(c, "decode_list_short_i64_json", &short_data, schema.clone());
+    let short_data = build_list_json(ROWS, SHORT_LIST_ELEMENTS);
+    bench_decode_schema(c, "decode_short_list_i64_json", &short_data, schema.clone());
 
     // Long lists: tests child element decode throughput (many elements per row)
-    let long_data = build_list_json(ROWS, LIST_LONG_ELEMENTS);
-    bench_decode_schema(c, "decode_list_long_i64_json", &long_data, schema);
+    let long_data = build_list_json(ROWS, LONG_LIST_ELEMENTS);
+    bench_decode_schema(c, "decode_long_list_i64_json", &long_data, schema);
 }
 
 fn bench_serialize_list(c: &mut Criterion) {
     let schema = build_list_schema();
 
-    let short_values = build_list_values(ROWS, LIST_SHORT_ELEMENTS);
-    c.bench_function("decode_list_short_i64_serialize", |b| {
+    let short_values = build_list_values(ROWS, SHORT_LIST_ELEMENTS);
+    c.bench_function("decode_short_list_i64_serialize", |b| {
+        b.iter(|| {
+            let mut decoder = ReaderBuilder::new(schema.clone())
+                .with_batch_size(BATCH_SIZE)
+                .build_decoder()
+                .unwrap();
+            decoder.serialize(&short_values).unwrap();
+            while let Some(_batch) = decoder.flush().unwrap() {}
+        })
+    });
+
+    let long_values = build_list_values(ROWS, LONG_LIST_ELEMENTS);
+    c.bench_function("decode_long_list_i64_serialize", |b| {
+        b.iter(|| {
+            let mut decoder = ReaderBuilder::new(schema.clone())
+                .with_batch_size(BATCH_SIZE)
+                .build_decoder()
+                .unwrap();
+            decoder.serialize(&long_values).unwrap();
+            while let Some(_batch) = decoder.flush().unwrap() {}
+        })
+    });
+}
+
+fn build_map_json(rows: usize, entries: usize) -> Vec<u8> {
+    let mut out = String::with_capacity(rows * (entries * 20 + 16));
+    for row in 0..rows {
+        out.push_str("{\"map\":{");
+        for i in 0..entries {
+            if i > 0 {
+                out.push(',');
+            }
+            write!(&mut out, "\"k{}\":{}", i, (row + i) as i64).unwrap();
+        }
+        out.push_str("}}\n");
+    }
+    out.into_bytes()
+}
+
+fn build_map_values(rows: usize, entries: usize) -> Vec<Value> {
+    let mut out = Vec::with_capacity(rows);
+    for row in 0..rows {
+        let mut inner = Map::with_capacity(entries);
+        for i in 0..entries {
+            inner.insert(
+                format!("k{i}"),
+                Value::Number(Number::from((row + i) as i64)),
+            );
+        }
+        let mut map = Map::with_capacity(1);
+        map.insert("map".to_string(), Value::Object(inner));
+        out.push(Value::Object(map));
+    }
+    out
+}
+
+fn build_map_schema() -> Arc<Schema> {
+    let entries_field = Arc::new(Field::new(
+        "entries",
+        DataType::Struct(
+            vec![
+                Field::new("keys", DataType::Utf8, false),
+                Field::new("values", DataType::Int64, true),
+            ]
+            .into(),
+        ),
+        false,
+    ));
+    Arc::new(Schema::new(vec![Field::new(
+        "map",
+        DataType::Map(entries_field, false),
+        false,
+    )]))
+}
+
+fn bench_decode_map(c: &mut Criterion) {
+    let schema = build_map_schema();
+
+    let small_data = build_map_json(ROWS, SMALL_MAP_ENTRIES);
+    bench_decode_schema(c, "decode_small_map_json", &small_data, schema.clone());
+
+    let large_data = build_map_json(ROWS, LARGE_MAP_ENTRIES);
+    bench_decode_schema(c, "decode_large_map_json", &large_data, schema);
+}
+
+fn bench_serialize_map(c: &mut Criterion) {
+    let schema = build_map_schema();
+
+    let small_values = build_map_values(ROWS, SMALL_MAP_ENTRIES);
+    c.bench_function("decode_small_map_serialize", |b| {
+        b.iter(|| {
+            let mut decoder = ReaderBuilder::new(schema.clone())
+                .with_batch_size(BATCH_SIZE)
+                .build_decoder()
+                .unwrap();
+            decoder.serialize(&small_values).unwrap();
+            while let Some(_batch) = decoder.flush().unwrap() {}
+        })
+    });
+
+    let large_values = build_map_values(ROWS, LARGE_MAP_ENTRIES);
+    c.bench_function("decode_large_map_serialize", |b| {
+        b.iter(|| {
+            let mut decoder = ReaderBuilder::new(schema.clone())
+                .with_batch_size(BATCH_SIZE)
+                .build_decoder()
+                .unwrap();
+            decoder.serialize(&large_values).unwrap();
+            while let Some(_batch) = decoder.flush().unwrap() {}
+        })
+    });
+}
+
+fn build_ree_json(rows: usize, run_length: usize) -> Vec<u8> {
+    let mut out = String::with_capacity(rows * 24);
+    for row in 0..rows {
+        let value = (row / run_length) as i64;
+        writeln!(&mut out, "{{\"val\":{value}}}").unwrap();
+    }
+    out.into_bytes()
+}
+
+fn build_ree_values(rows: usize, run_length: usize) -> Vec<Value> {
+    let mut out = Vec::with_capacity(rows);
+    for row in 0..rows {
+        let value = (row / run_length) as i64;
+        let mut map = Map::with_capacity(1);
+        map.insert("val".to_string(), Value::Number(Number::from(value)));
+        out.push(Value::Object(map));
+    }
+    out
+}
+
+fn build_ree_schema() -> Arc<Schema> {
+    let ree_type = DataType::RunEndEncoded(
+        Arc::new(Field::new("run_ends", DataType::Int32, false)),
+        Arc::new(Field::new("values", DataType::Int64, true)),
+    );
+    Arc::new(Schema::new(vec![Field::new("val", ree_type, false)]))
+}
+
+fn bench_decode_ree(c: &mut Criterion) {
+    let schema = build_ree_schema();
+
+    let short_data = build_ree_json(ROWS, SHORT_REE_RUN_LENGTH);
+    bench_decode_schema(c, "decode_short_ree_runs_json", &short_data, schema.clone());
+
+    let long_data = build_ree_json(ROWS, LONG_REE_RUN_LENGTH);
+    bench_decode_schema(c, "decode_long_ree_runs_json", &long_data, schema);
+}
+
+fn bench_serialize_ree(c: &mut Criterion) {
+    let schema = build_ree_schema();
+
+    let short_values = build_ree_values(ROWS, SHORT_REE_RUN_LENGTH);
+    c.bench_function("decode_short_ree_runs_serialize", |b| {
         b.iter(|| {
             let mut decoder = ReaderBuilder::new(schema.clone())
                 .with_batch_size(BATCH_SIZE)
@@ -312,8 +481,8 @@ fn bench_serialize_list(c: &mut Criterion) {
         })
     });
 
-    let long_values = build_list_values(ROWS, LIST_LONG_ELEMENTS);
-    c.bench_function("decode_list_long_i64_serialize", |b| {
+    let long_values = build_ree_values(ROWS, LONG_REE_RUN_LENGTH);
+    c.bench_function("decode_long_ree_runs_serialize", |b| {
         b.iter(|| {
             let mut decoder = ReaderBuilder::new(schema.clone())
                 .with_batch_size(BATCH_SIZE)
@@ -402,6 +571,10 @@ criterion_group!(
     bench_wide_projection,
     bench_decode_list,
     bench_serialize_list,
+    bench_decode_map,
+    bench_serialize_map,
+    bench_decode_ree,
+    bench_serialize_ree,
     bench_schema_inference
 );
 criterion_main!(benches);