docs/source/extension-guide/other-components.md

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(extension_other_hooks)=

# Optimizer rules and configuration

Two hooks contribute things that are neither data nor functions: a rewrite pass
over physical plans, and typed entries in the session config. Both take no
argument and both are implemented in [`datafusion-ffi-example`].

## A physical optimizer rule

**`__datafusion_physical_optimizer_rule__`** contributes a rule that rewrites
physical plans, installed with
{py:meth}`~datafusion.SessionContext.add_physical_optimizer_rule`. Reach for
this rather than a {doc}`query planner <query-planners>` when you want to
adjust the plan DataFusion produced rather than produce it yourself — it is
much the smaller commitment, and rules accumulate where planners nest.

```rust
fn __datafusion_physical_optimizer_rule__<'py>(
    &self,
    py: Python<'py>,
) -> PyResult<Bound<'py, PyCapsule>> {
    let rule: Arc<dyn PhysicalOptimizerRule + Send + Sync> = Arc::new(self.clone());
    let runtime = get_tokio_runtime().handle().clone();
    let ffi = FFI_PhysicalOptimizerRule::new(rule, Some(runtime));

    PyCapsule::new_with_value(py, ffi, cr"datafusion_physical_optimizer_rule")
}
```

## Typed configuration

**`__datafusion_extension_options__`** contributes typed configuration entries
that your components can read back out of the session config, installed with
{py:meth}`SessionConfig.with_extension <datafusion.SessionConfig.with_extension>`.
`FFI_ExtensionOptions` carries no version field, so it is one of the three
components that cannot be version-checked on import.

```rust
fn __datafusion_extension_options__<'py>(
    &self,
    py: Python<'py>,
) -> PyResult<Bound<'py, PyCapsule>> {
    let mut config = FFI_ExtensionOptions::default();
    config
        .add_config(self)
        .map_err(|e| PyRuntimeError::new_err(e.to_string()))?;

    PyCapsule::new_with_value(py, config, cr"datafusion_extension_options")
}
```

[`datafusion-ffi-example`]: https://github.com/apache/datafusion-python/tree/main/examples/datafusion-ffi-example