askalt commented on issue #19351:
URL: https://github.com/apache/datafusion/issues/19351#issuecomment-3660882807
Noted:
1) `datafusion-execution` does not depend on physical plan so it would be
clumsy to store some physical plan specific state within `TaskContext`.
Decided for now to extend `TaskContext` within `datafusion-physical-plan`:
```rust
/// Plan execution context.
///
/// [`ExecutionContext`] contains the state required during a node
/// execution, including pointers to the children contexts.
///
/// # Note
///
/// A [`ExecutionContext`] tree built on [`ExecutionPlan::execute`] stage
/// has the same form as the [`ExecutionPlan`] tree itself. It is intended
/// to store the plan state that is created during the plan execution stage
/// and should be associated with the plan nodes later. For example, metrics.
///
/// [`ExecutionPlan`]: crate::ExecutionPlan
/// [`ExecutionPlan::execute`]: crate::ExecutionPlan::execute
///
pub struct ExecutionContext {
/// Corresponding task context.
pub task_context: Arc<TaskContext>,
/// Plan specific state initialized once per execution.
pub plan_state: OnceAsync<Arc<dyn PlanState>>,
/// Metrics associated with this plan node.
pub metrics: ExecutionPlanMetricsSet,
/// Context for each plan children.
pub children_context: Vec<Box<ExecutionContext>>,
}
```
Instead of storing `pointer -> state` mapping (which looks clumsy), there is
the separate tree to keep execution stage related plan state.
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