rluvaton commented on code in PR #20314:
URL: https://github.com/apache/datafusion/pull/20314#discussion_r2841341122
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datafusion/physical-plan/src/sorts/stream.rs:
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@@ -276,3 +280,159 @@ impl<T: CursorArray> PartitionedStream for
FieldCursorStream<T> {
}))
}
}
+
+/// A lazy, memory-efficient sort iterator used as a fallback during aggregate
+/// spill when there is not enough memory for an eager sort (which requires ~2x
+/// peak memory to hold both the unsorted and sorted copies simultaneously).
+///
+/// On the first call to `next()`, a sorted index array (`UInt32Array`) is
+/// computed via `lexsort_to_indices`. Subsequent calls yield chunks of
+/// `batch_size` rows by `take`-ing from the original batch using slices of
+/// this index array. Each `take` copies data for the chunk (not zero-copy),
+/// but only one chunk is live at a time since the caller consumes it before
+/// requesting the next. Once all rows have been yielded, the original batch
+/// and index array are dropped to free memory.
+///
+/// The caller must reserve `sizeof(batch) + sizeof(one chunk)` for this
iterator,
+/// and free the reservation once the iterator is depleted.
+pub(crate) struct IncrementalSortIterator {
Review Comment:
since `sort_batch_chunked` does the same thing but return `Vec<RecordBatch>`
I would update it to use this iterator
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