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# Upgrade Guides

## DataFusion 56.0.0

**Note:** DataFusion `56.0.0` has not been released yet. The information provided
in this section pertains to features and changes that have already been merged
to the main branch and are awaiting release in this version.

### `datafusion.optimizer.use_statistics_registry` is deprecated and ignored

The `datafusion.optimizer.use_statistics_registry` config flag is deprecated and
now ignored (setting it emits a deprecation warning). The pluggable
`StatisticsRegistry` is always consulted during the single statistics walk:
providers registered on the session take effect directly. With no providers
registered the registry is a no-op, so default behavior is unchanged from the
previous default (`use_statistics_registry = false`).

**Who is affected:**

- Anyone who set `datafusion.optimizer.use_statistics_registry`. The setting is
  still accepted (with a deprecation warning) but has no effect, and will be
  removed in a future release.

**Migration guide:**

- Drop any `use_statistics_registry` setting.
- To use statistics providers, register them on the session with
  `SessionStateBuilder::with_statistics_registry(...)`. To keep the built-in
  NDV-aware providers the flag previously enabled, register
  `StatisticsRegistry::default_with_builtin_providers()`.
- To opt out, register nothing (the default).

### `DefaultStatisticsProvider` is deprecated

`datafusion_physical_plan::operator_statistics::DefaultStatisticsProvider` is
deprecated. It is redundant: the statistics walk (`StatisticsContext`) falls back
to each operator's `statistics_from_inputs` when the provider chain delegates or
is empty, so a terminal "default" provider is no longer needed. It is no longer
part of `StatisticsRegistry::default_with_builtin_providers()`.

**Migration guide:**

- Remove `DefaultStatisticsProvider` from any custom provider chain; register no
  terminal provider instead (the walk falls back on its own).

### `StatisticsRegistry::compute` and `compute_base` are deprecated

Use the walk instead:

```rust
StatisticsContext::new_with_registry(registry)
    .compute_extended(plan, &StatisticsArgs::new())?; // or .compute(...) for core Statistics
```