hhhizzz commented on code in PR #10735:
URL: https://github.com/apache/arrow-rs/pull/10735#discussion_r3809556627
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parquet/src/arrow/arrow_reader/selection/cursor.rs:
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@@ -176,10 +176,11 @@ impl SelectorsCursor {
/// LoadedRowRanges: [0, 4) [10, 12)
/// ```
///
-/// The first chunk decodes `[0, 4)` with mask `1000`. The next chunk skips to
-/// row 11 and decodes `[11, 12)` with mask `1`. The loaded ranges are decode
-/// boundaries, not output batch boundaries: [`ParquetRecordBatchReader`]
-/// accumulates both chunks and applies the combined mask `10001` once.
+/// The first chunk decodes `[0, 1)` with mask `1`. The next chunk skips to row
+/// 11 and decodes `[11, 12)` with mask `1`. Trimming trailing skipped rows
from
Review Comment:
Thanks, agreed. I rewrote the MaskCursor documentation to state the cursor
invariant directly: when loaded ranges are present, every returned chunk ends
at a selected row and contains no trailing unselected rows. I moved the caching
dependency to CachedArrayReader::fetch_batch, where the full-batch fallback
actually relies on that guarantee, and kept the predicate-side comment focused
on expanding cached columns to cache batch boundaries.
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