XiangpengHao commented on code in PR #6155:
URL: https://github.com/apache/arrow-rs/pull/6155#discussion_r1711431774
##########
arrow-buffer/src/buffer/null.rs:
##########
@@ -15,35 +15,66 @@
// specific language governing permissions and limitations
// under the License.
+use std::sync::atomic::{AtomicI64, Ordering};
+
use crate::bit_iterator::{BitIndexIterator, BitIterator, BitSliceIterator};
use crate::buffer::BooleanBuffer;
use crate::{Buffer, MutableBuffer};
+const UNINITIALIZED_NULL_COUNT: i64 = -1;
+
+#[derive(Debug)]
+pub enum NullCount {
+ Eager(usize),
+ Lazy(AtomicI64),
Review Comment:
I feel the state here is a bit complicated, here we have three states:
`Eager`, `Lazy (initialized)`, `Lazy (uninitialized)`. And we use both enum and
fence value to differentiate them.
I wonder if we can simplify this with just two states: uninitialized and
initialized; and when we try to read a uninitialized value, we count the value
and set it to initialized state.
```rust
struct NullCount {
val: AtomicI64,
}
impl NullCount {
fn get(&self, ...) -> i64 {
let val = self.val.load(...);
if val == UNINIT {
val.store(cal_null_count);
} else {
return val
}
}
}
```
This way we only have two states to manage, and we also keep the NullCount
to be 8 byte, instead of the current 24 bytes, which might help with performance
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