perf: improve deserialization of value encoding for struct/list (#5897)

improve value encoding for struct/list

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

src/common/src/util/value_encoding/mod.rs

@@ -176,21 +176,21 @@ fn deserialize_value(ty: &DataType, data: &mut impl Buf) -> Result<Datum> {
 }
 
 fn deserialize_struct(struct_def: &StructType, data: &mut impl Buf) -> Result<ScalarImpl> {
-    let field_values = struct_def
-        .fields
-        .iter()
-        .map(|field_type| inner_deserialize_datum(data, field_type))
-        .collect::<Result<Vec<Datum>>>()?;
+    let num_fields = struct_def.fields.len();
+    let mut field_values = Vec::with_capacity(num_fields);
+    for field_type in &struct_def.fields {
+        field_values.push(inner_deserialize_datum(data, field_type)?);
+    }
 
     Ok(ScalarImpl::Struct(StructValue::new(field_values)))
 }
 
 fn deserialize_list(item_type: &DataType, data: &mut impl Buf) -> Result<ScalarImpl> {
     let len = data.get_u32_le();
-    let values = (0..len)
-        .map(|_| inner_deserialize_datum(data, item_type))
-        .collect::<Result<Vec<Datum>>>()?;
-
+    let mut values = Vec::with_capacity(len as usize);
+    for _ in 0..len {
+        values.push(inner_deserialize_datum(data, item_type)?);
+    }
     Ok(ScalarImpl::List(ListValue::new(values)))
 }