baiguoname commented on issue #17899:
URL: https://github.com/apache/datafusion/issues/17899#issuecomment-3378314459
> Supporting retract batch is somewhat more complicated as that means the
accumulator needs to hold the entire window of values.
>
> I suggest you file a separate ticket to track supporting retract_batch
For test, I implement `MyTrivalFirstValueAccumulator` in the similar of
`TrivalFirstValueAccumulator` in this way:
```rust
#[derive(Debug, Default)]
pub struct MyTrivalFirstValueAccumulator {
window_values: VecDeque<ScalarValue>,
}
impl Accumulator for MyTrivalFirstValueAccumulator {
fn state(&mut self) -> Result<Vec<ScalarValue>> {
Ok(vec![ScalarValue::from(0), ScalarValue::from(true)])
}
fn update_batch(&mut self, values: &[ArrayRef]) -> Result<()> {
let now_value = get_row_at_idx(values, 0)?.remove(0);
self.window_values.push_back(now_value);
Ok(())
}
fn merge_batch(&mut self, _states: &[ArrayRef]) -> Result<()> {
unreachable!("not call");
}
fn retract_batch(&mut self, _values: &[ArrayRef]) -> Result<()> {
self.window_values.pop_front();
Ok(())
}
fn supports_retract_batch(&self) -> bool {
true
}
fn evaluate(&mut self) -> Result<ScalarValue> {
Ok(self.window_values[0].clone())
}
fn size(&self) -> usize {
size_of_val(self) - size_of_val(&self.window_values)
}
}
```
And their performance are close.
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