gabotechs commented on issue #22708:
URL: https://github.com/apache/datafusion/issues/22708#issuecomment-4600043507
There's one subtle different from `EvaluationType::Eager`'s definition and
what `BufferExec` does:
```rust
/// The stream generated by [`execute`](ExecutionPlan::execute) eagerly
generates `RecordBatch`
/// in one or more spawned Tokio tasks. Eager evaluation is only started
the first time
/// `Stream::poll_next` is called.
/// Examples of eager operators are repartition, coalesce partitions,
and sort preserving merge.
///
/// Eager operators are also known as a data-driven operators.
Eager,
```
`BufferExec` does eagerly generates `RecordBatches` on a tokio spawned task,
but it does not start evaluation after `Stream::poll_next` is called. It starts
evaluation whether `Stream::poll_next` is called or not, which is the main
point and the main reason why it brings performance benefits at the cost of
memory usage.
That being said, I agree that it's more accurate if both declare
`EvaluationType::Eager`
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