zhuqi-lucas commented on code in PR #10158:
URL: https://github.com/apache/arrow-rs/pull/10158#discussion_r3457002178
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parquet/src/arrow/push_decoder/remaining.rs:
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@@ -93,6 +93,63 @@ impl RowGroupFrontier {
self.budget = budget;
}
+ /// Peek at the next row-group index `next_readable_row_group` would
+ /// hand out, without mutating any state. Returns `None` if every
+ /// remaining row group would be skipped under the current
+ /// selection/budget, or if the queue is empty.
+ ///
+ /// Mirrors the structure of `next_readable_row_group` but only walks
+ /// borrowed state — used by
[`super::ParquetPushDecoder::peek_next_row_group`]
+ /// to let adaptive callers (e.g. dynamic row-group pruners or per-RG
+ /// `RowFilter` toggles) keep their per-RG state in lock-step with
+ /// the reader the decoder is about to emit.
+ fn peek_next_row_group(&self) -> Result<Option<usize>, ParquetError> {
+ // Short-circuit: budget exhausted or selection drained ⇒ same
+ // outcome as `next_readable_row_group`'s early return.
+ if self.budget.is_exhausted()
+ || self
+ .selection
+ .as_ref()
+ .is_some_and(|selection| selection.row_count() == 0)
+ {
+ return Ok(None);
+ }
+
+ // We may have to walk past row groups whose split selection is
+ // empty. Cloning the selection lets us run the same `split_off`
+ // logic without disturbing the real one.
+ let mut selection = self.selection.clone();
Review Comment:
Good point!
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