tobixdev commented on code in PR #18254:
URL: https://github.com/apache/datafusion/pull/18254#discussion_r2466160581
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datafusion/physical-plan/src/recursive_query.rs:
##########
@@ -434,5 +452,55 @@ impl RecordBatchStream for RecursiveQueryStream {
}
}
+/// Deduplicator based on a hash table.
+struct DistinctDeduplicator {
+ /// Grouped rows used for distinct
+ group_values: Box<dyn GroupValues>,
+ reservation: MemoryReservation,
+ intern_output_buffer: Vec<usize>,
+}
+
+impl DistinctDeduplicator {
+ fn new(schema: SchemaRef, task_context: &TaskContext) -> Result<Self> {
+ let group_values = new_group_values(schema, &GroupOrdering::None)?;
+ let reservation = MemoryConsumer::new("RecursiveQueryHashTable")
+ .register(task_context.memory_pool());
+ Ok(Self {
+ group_values,
+ reservation,
+ intern_output_buffer: Vec::new(),
+ })
+ }
+
+ fn deduplicate(&mut self, batch: &RecordBatch) -> Result<RecordBatch> {
+ // We use the hash table to allocate new group ids.
+ // If they are new, i.e., if they have ids >= length before interning,
we keep them.
+ // We also detect duplicates by enforcing that group ids are
increasing.
+ let size_before = self.group_values.len();
+ self.intern_output_buffer.reserve(batch.num_rows());
+ self.group_values
+ .intern(batch.columns(), &mut self.intern_output_buffer)?;
+ let mask = are_increasing_mask(&self.intern_output_buffer,
size_before);
+ self.intern_output_buffer.clear();
+ // We update the reservation to reflect the new size of the hash table.
+ self.reservation.try_resize(self.group_values.size())?;
+ Ok(filter_record_batch(batch, &mask)?)
+ }
+}
+
+/// Return a mask, each element true if the value is greater than all previous
ones and greater or equal than the min_value
+fn are_increasing_mask(values: &[usize], mut min_value: usize) -> BooleanArray
{
Review Comment:
That's perfectly fine. Just a suggestion :+1:
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