add to upgrade guide

Author: adriangb

docs/source/library-user-guide/upgrading.md

@@ -100,6 +100,16 @@ This version of DataFusion upgrades the underlying Apache Arrow implementation
 to version `56.0.0`. See the [release notes](https://github.com/apache/arrow-rs/releases/tag/56.0.0)
 for more details.
 
+### Added `ExecutionPlan::reset_state`
+
+In order to fix a bug in DataFusion `49.0.0` where dynamic filters (currently only generated in the precense of a query such as `ORDER BY ... LIMIT ...`)
+produced incorrect results in recursive queries, a new method `reset_state` has been added to the `ExecutionPlan` trait.
+
+Any `ExecutionPlan` that needs to maintain internal state or references to other nodes in the execution plan tree should implement this method to reset that state.
+See [#17028] for more details and an example implementation for `SortExec`.
+
+[#17028]: https://github.com/apache/datafusion/pull/17028
+
 ## DataFusion `49.0.0`
 
 ### `MSRV` updated to 1.85.1