Adjust calculation for validity bitmap

arrow/src/array/array.rs

@@ -585,7 +585,6 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::iter::FromIterator;
 
     #[test]
     fn test_empty_primitive() {
@@ -683,6 +682,10 @@ mod tests {
             std::mem::size_of::<NullArray>(),
             null_arr.get_array_memory_size()
         );
+        assert_eq!(
+            std::mem::size_of::<NullArray>(),
+            std::mem::size_of::<ArrayData>(),
+        );
     }
 
     #[test]
@@ -708,6 +711,15 @@ mod tests {
                 .build(),
         );
 
+        // expected size is the size of the PrimitiveArray struct,
+        // which includes the optional validity buffer
+        // plus one buffer on the heap
+        assert_eq!(
+            std::mem::size_of::<PrimitiveArray<Int64Type>>()
+                + std::mem::size_of::<Buffer>(),
+            empty_with_bitmap.get_array_memory_size()
+        );
+
         // substract empty array to avoid magic numbers for the size of additional fields
         // the size of the validity bitmap is rounded up to 64 bytes
         assert_eq!(

arrow/src/array/data.rs

@@ -358,11 +358,14 @@ impl ArrayData {
 
         // Calculate rest of the fields top down which contain actual data
         for buffer in &self.buffers {
-            size += mem::size_of_val(&buffer);
+            size += mem::size_of::<Buffer>();
             size += buffer.capacity();
         }
         if let Some(bitmap) = &self.null_bitmap {
-            size += bitmap.get_array_memory_size()
+            // this includes the size of the bitmap struct itself, since it is stored directly in
+            // this struct we already counted those bytes in the size_of_val(self) above
+            size += bitmap.get_array_memory_size();
+            size -= mem::size_of::<Bitmap>();
         }
         for child in &self.child_data {
             size += child.get_array_memory_size();