alamb commented on code in PR #18254:
URL: https://github.com/apache/datafusion/pull/18254#discussion_r2560117640
##########
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:
I also found this confusing. Some suggestions:
1. Rename the function to `new_groups_mask` to reflect what it does
2. Rename `min_value` to `max_seen_group_id` or `max_emitted` or something
like that.
##########
datafusion/physical-plan/src/recursive_query.rs:
##########
@@ -428,5 +446,58 @@ 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(),
+ })
+ }
+
+ /// Remove duplicated rows from the given batch, keeping a state between
batches.
+ ///
+ /// We use a hash table to allocate new group ids for the new rows.
+ /// [`GroupValues`] allocate increasing group ids.
+ /// Hence, if groups (i.e., rows) are now, then they have ids >= length
before interning, we keep them.
Review Comment:
```suggestion
/// Hence, if groups (i.e., rows) are new, then they have ids >= length
before interning, we keep them.
```
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