alamb commented on code in PR #16196:
URL: https://github.com/apache/datafusion/pull/16196#discussion_r2114732484
##########
datafusion/physical-plan/src/aggregates/no_grouping.rs:
##########
@@ -77,6 +77,9 @@ impl AggregateStream {
let baseline_metrics = BaselineMetrics::new(&agg.metrics, partition);
let input = agg.input.execute(partition, Arc::clone(&context))?;
+ // Wrap no‐grouping aggregates in our YieldStream
Review Comment:
I think we should add the rationale for doing this here, otherwise it is not
clear
For example, something like
```suggestion
// Yield control back to tokio after a certain number of batches so
it can check for cancellation.
// See https://github.com/apache/datafusion/issues/16193
```
##########
datafusion/physical-plan/src/aggregates/no_grouping.rs:
##########
@@ -170,6 +173,65 @@ impl AggregateStream {
}
}
+/// A stream that yields batches of data, yielding control back to the executor
+pub struct YieldStream {
+ inner: SendableRecordBatchStream,
+ batches_processed: usize,
+ buffer: Option<Result<RecordBatch>>,
+}
+
+impl YieldStream {
Review Comment:
This is a neat structure -- think it is more generally useful. Perhaps we
could put it into somewhere that it is more likely discoverable, such as
https://github.com/apache/datafusion/tree/main/datafusion/common-runtime/src
##########
datafusion/physical-plan/src/aggregates/no_grouping.rs:
##########
@@ -170,6 +173,65 @@ impl AggregateStream {
}
}
+/// A stream that yields batches of data, yielding control back to the executor
Review Comment:
```suggestion
/// A stream that yields batches of data, yielding control back to the
executor every `YIELD_BATCHES` batches
///
/// This can be useful for to allow operators that might not yield to check
for cancellation
```
##########
datafusion/physical-plan/src/aggregates/no_grouping.rs:
##########
@@ -170,6 +173,65 @@ impl AggregateStream {
}
}
+/// A stream that yields batches of data, yielding control back to the executor
+pub struct YieldStream {
+ inner: SendableRecordBatchStream,
+ batches_processed: usize,
+ buffer: Option<Result<RecordBatch>>,
+}
+
+impl YieldStream {
+ pub fn new(inner: SendableRecordBatchStream) -> Self {
+ Self {
+ inner,
+ batches_processed: 0,
+ buffer: None,
+ }
+ }
+}
+
+// Stream<Item = Result<RecordBatch>> to poll_next_unpin
+impl Stream for YieldStream {
+ type Item = Result<RecordBatch>;
+
+ fn poll_next(
+ mut self: std::pin::Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<Self::Item>> {
+ const YIELD_BATCHES: usize = 64;
Review Comment:
I think this would be easier to find and make the code easer to undertand of
we moved it to a separate `const` in the module and add comments that describe
it (aka the number of batches returned prior to checking for drop)
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