2010YOUY01 commented on code in PR #15409:
URL: https://github.com/apache/datafusion/pull/15409#discussion_r2065594544
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datafusion/datasource/src/memory.rs:
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@@ -723,6 +761,222 @@ impl MemorySourceConfig {
pub fn original_schema(&self) -> SchemaRef {
Arc::clone(&self.schema)
}
+
+ /// Repartition while preserving order.
+ ///
+ /// Returns `Ok(None)` if cannot fulfill the requested repartitioning, such
+ /// as having too few batches to fulfill the `target_partitions` or if
unable
+ /// to preserve output ordering.
+ fn repartition_preserving_order(
+ &self,
+ target_partitions: usize,
+ output_ordering: LexOrdering,
+ ) -> Result<Option<Vec<Vec<RecordBatch>>>> {
+ if !self.eq_properties().ordering_satisfy(&output_ordering) {
+ Ok(None)
+ } else if self.partitions.len() == 1 {
+ self.repartition_evenly_by_size(target_partitions)
+ } else {
Review Comment:
It would be great to include a simple example to explain this code block,
like how is an input table be repartitioned, what is the key in the max heap,
and how the state changes during each loop step.
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