rename capacity to item_capacity in bytes and utf8 array builder

Signed-off-by: Runji Wang <[email protected]>

src/common/src/array/bytes_array.rs

@@ -142,19 +142,24 @@ pub struct BytesArrayBuilder {
 impl ArrayBuilder for BytesArrayBuilder {
     type ArrayType = BytesArray;
 
-    fn new(capacity: usize) -> Self {
-        let mut offset = Vec::with_capacity(capacity + 1);
+    /// Creates a new `BytesArrayBuilder`.
+    ///
+    /// `item_capacity` is the number of items to pre-allocate. The size of the preallocated
+    /// buffer of offsets is the number of items plus one.
+    /// No additional memory is pre-allocated for the data buffer.
+    fn new(item_capacity: usize) -> Self {
+        let mut offset = Vec::with_capacity(item_capacity + 1);
         offset.push(0);
         Self {
             offset,
-            data: Vec::with_capacity(capacity),
+            data: Vec::with_capacity(0),
             bitmap: BitmapBuilder::with_capacity(capacity),
         }
     }
 
-    fn with_type(capacity: usize, ty: DataType) -> Self {
+    fn with_type(item_capacity: usize, ty: DataType) -> Self {
         assert_eq!(ty, DataType::Bytea);
-        Self::new(capacity)
+        Self::new(item_capacity)
     }
 
     fn append_n<'a>(&'a mut self, n: usize, value: Option<&'a [u8]>) {

src/common/src/array/utf8_array.rs

@@ -123,15 +123,20 @@ pub struct Utf8ArrayBuilder {
 impl ArrayBuilder for Utf8ArrayBuilder {
     type ArrayType = Utf8Array;
 
-    fn new(capacity: usize) -> Self {
+    /// Creates a new `Utf8ArrayBuilder`.
+    ///
+    /// `item_capacity` is the number of items to pre-allocate. The size of the preallocated
+    /// buffer of offsets is the number of items plus one.
+    /// No additional memory is pre-allocated for the data buffer.
+    fn new(item_capacity: usize) -> Self {
         Self {
-            bytes: BytesArrayBuilder::new(capacity),
+            bytes: BytesArrayBuilder::new(item_capacity),
         }
     }
 
-    fn with_type(capacity: usize, ty: DataType) -> Self {
+    fn with_type(item_capacity: usize, ty: DataType) -> Self {
         assert_eq!(ty, DataType::Varchar);
-        Self::new(capacity)
+        Self::new(item_capacity)
     }
 
     #[inline]