adriangb commented on code in PR #10158:
URL: https://github.com/apache/arrow-rs/pull/10158#discussion_r3453537189
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parquet/src/arrow/push_decoder/mod.rs:
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@@ -538,6 +538,31 @@ impl ParquetPushDecoder {
self.state.row_groups_remaining()
}
+ /// Returns the file-level row-group index that the next call to
+ /// [`Self::try_next_reader`] will yield a reader for, after applying
+ /// any internal skipping (row selection emptiness, exhausted budget,
+ /// finished state). Returns `Ok(None)` when:
+ /// - the decoder has no more row groups to read,
+ /// - the decoder is currently inside a row group (consumers should
+ /// call [`Self::is_at_row_group_boundary`] first), or
+ /// - every remaining row group would be skipped.
+ ///
+ /// Returns `Err` when reading row-group metadata fails (e.g.
+ /// `usize` overflow on 32-bit targets), matching the error surface
+ /// of `try_next_reader` so peek and read paths report errors
+ /// consistently.
+ ///
+ /// This is a read-only peek: it does not mutate decoder state. It is
+ /// useful for adaptive callers that maintain per-row-group state in
+ /// lock-step with the decoder (e.g. dynamic row-group pruners or
+ /// per-RG `RowFilter` toggles): without this peek the caller has no
+ /// way to know which row group the next reader actually corresponds
+ /// to, because [`Self::try_next_reader`] may silently advance past
+ /// row groups whose row selection is empty.
+ pub fn peek_next_row_group(&self) -> Result<Option<usize>, ParquetError> {
+ self.state.peek_next_row_group()
+ }
+
Review Comment:
Should we make this `peek_remaining_row_groups()`? That might enable more
usages in the future.
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