kosiew commented on code in PR #16926:
URL: https://github.com/apache/datafusion/pull/16926#discussion_r2233803439
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datafusion/execution/src/memory_pool/memory_report.rs:
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@@ -0,0 +1,118 @@
+use super::{human_readable_size, MemoryReservation};
+use crate::memory_pool::pool::{
+ FairSpillPool, GreedyMemoryPool, TrackConsumersPool, UnboundedMemoryPool,
+};
+use crate::memory_pool::MemoryPool;
+use datafusion_common::Result;
+use datafusion_expr::Accumulator;
+use std::any::Any;
+
+/// Helper trait to provide memory usage breakdowns for debugging.
+///
+/// Implemented for [`MemoryReservation`] and any [`Accumulator`] via a blanket
+/// implementation that relies on [`Accumulator::size`].
+///
+/// # Example
+/// ```
+/// # use std::sync::Arc;
+/// # use datafusion_execution::memory_pool::{ExplainMemory, GreedyMemoryPool,
MemoryConsumer};
+/// let pool = Arc::new(GreedyMemoryPool::new(1024));
+/// let mut reservation = MemoryConsumer::new("example").register(&pool);
+/// reservation.try_grow(256).unwrap();
+/// println!("{}", reservation.explain_memory().unwrap());
+/// ```
+pub trait ExplainMemory {
+ /// Returns a human readable string describing memory usage.
+ fn explain_memory(&self) -> Result<String>;
+}
+
+impl ExplainMemory for MemoryReservation {
+ fn explain_memory(&self) -> Result<String> {
+ Ok(format!(
+ "{}#{} reserved {}",
+ self.consumer().name(),
+ self.consumer().id(),
+ human_readable_size(self.size())
+ ))
+ }
+}
+
+impl<T: Accumulator + ?Sized> ExplainMemory for T {
Review Comment:
Hey @rluvaton! ๐
You're totally right to be cautious โ that blanket impl of ExplainMemory for
T where T: Accumulator will indeed block any other downstream impls of
ExplainMemory for overlapping traits like T: MyTrait, due to Rust's coherence
and orphan rules.
๐ก Workaround: You can safely achieve what you want using a newtype pattern.
That way, you avoid trait conflicts while still providing a blanket impl.
Hereโs a minimal example:
```rust
// Newtype wrapper
struct AccumExplainer<T: Accumulator>(T);
// Blanket impl only applies to the wrapper, not all T
impl<T: Accumulator> ExplainMemory for AccumExplainer<T> {
fn explain(&self) -> String {
format!("Memory usage: {}", self.0.accumulate())
}
}
// Convenience (optional)
impl<T: Accumulator> From<T> for AccumExplainer<T> {
fn from(inner: T) -> Self {
Self(inner)
}
}
```
You can now wrap any Accumulator type like this:
```rust
fn explain_it<T: Accumulator>(thing: T) {
let wrapped = AccumExplainer::from(thing);
println!("{}", wrapped.explain());
}
```
This gives you a clean, conflict-free path to implement ExplainMemory
broadly without locking out other impls for T in the future.
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