Dandandan commented on PR #15380:
URL: https://github.com/apache/datafusion/pull/15380#issuecomment-2809508850
So to change it in your diff (didn't change the documentation).
I would like to keep the original `StreamingMergeBuilder` case and the `if
self.reservation.size() < self.sort_in_place_threshold_bytes` expression so
that we only have the "avoid concat for non-sort columns" optimization in place
and see if this improves on all sort queries.
```diff
- // If less than sort_in_place_threshold_bytes, concatenate and sort
in place
- if self.reservation.size() < self.sort_in_place_threshold_bytes {
- // Concatenate memory batches together and sort
- let batch = concat_batches(&self.schema, &self.in_mem_batches)?;
- self.in_mem_batches.clear();
- self.reservation
- .try_resize(get_reserved_byte_for_record_batch(&batch))
- .map_err(Self::err_with_oom_context)?;
- let reservation = self.reservation.take();
- return self.sort_batch_stream(batch, metrics, reservation);
+ let mut columns_by_expr: Vec<Vec<ArrayRef>> = vec![vec![];
self.expr.len()];
+ for batch in &self.in_mem_batches {
+ for (i, expr) in self.expr.iter().enumerate() {
+ let col = expr.evaluate_to_sort_column(batch)?.values;
+ columns_by_expr[i].push(col);
+ }
}
- let streams = std::mem::take(&mut self.in_mem_batches)
- .into_iter()
- .map(|batch| {
- let metrics = self.metrics.baseline.intermediate();
- let reservation = self
- .reservation
- .split(get_reserved_byte_for_record_batch(&batch));
- let input = self.sort_batch_stream(batch, metrics,
reservation)?;
- Ok(spawn_buffered(input, 1))
- })
- .collect::<Result<_>>()?;
+ // For each sort expression, concatenate arrays from all batches
into one global array
+ let mut sort_columns = Vec::with_capacity(self.expr.len());
+ for (arrays, expr) in
columns_by_expr.into_iter().zip(self.expr.iter()) {
+ let array = concat(
+ &arrays
+ .iter()
+ .map(|a| a.as_ref())
+ .collect::<Vec<&dyn Array>>(),
+ )?;
+ sort_columns.push(SortColumn {
+ values: array,
+ options: expr.options.into(),
+ });
+ }
- let expressions: LexOrdering = self.expr.iter().cloned().collect();
+ // ===== Phase 2: Compute global sorted indices =====
+ // Use `lexsort_to_indices` to get global row indices in sorted
order (as if all batches were concatenated)
+ let indices = lexsort_to_indices(&sort_columns, None)?;
- StreamingMergeBuilder::new()
- .with_streams(streams)
- .with_schema(Arc::clone(&self.schema))
- .with_expressions(expressions.as_ref())
- .with_metrics(metrics)
- .with_batch_size(self.batch_size)
- .with_fetch(None)
- .with_reservation(self.merge_reservation.new_empty())
- .build()
+ // ===== Phase 3: Reorder each column using the global sorted
indices =====
+ let num_columns = self.schema.fields().len();
+
+ let batch_indices: Vec<(usize, usize)> = self
+ .in_mem_batches
+ .iter()
+ .enumerate()
+ .map(|(batch_id, batch)| (0..batch.num_rows()).map(move |i|
(batch_id, i)))
+ .flatten()
+ .collect();
+
+ // For each column:
+ // 1. Concatenate all batch arrays for this column (in the same
order as assumed by `lexsort_to_indices`)
+ // 2. Use Arrow's `take` function to reorder the column by sorted
indices
+ let interleave_indices: Vec<(usize, usize)> = indices
+ .values()
+ .iter()
+ .map(|x| batch_indices[*x as usize])
+ .collect();
+ // Build a RecordBatch from the sorted columns
+
+ let batches: Vec<&RecordBatch> =
self.in_mem_batches.iter().collect();
+
+ let sorted_batch =
+ interleave_record_batch(batches.as_ref(), &interleave_indices)?;
+ // Clear in-memory batches and update reservation
+ self.in_mem_batches.clear();
+ self.reservation
+ .try_resize(get_reserved_byte_for_record_batch(&sorted_batch))?;
+ let reservation = self.reservation.take();
+
+ // ===== Phase 4: Construct the resulting stream =====
+ let stream = futures::stream::once(async move {
+ let _timer = metrics.elapsed_compute().timer();
+ metrics.record_output(sorted_batch.num_rows());
+ drop(reservation);
+ Ok(sorted_batch)
+ });
+
+ Ok(Box::pin(RecordBatchStreamAdapter::new(
+ self.schema.clone(),
+ stream,
+ )))
```
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