Revert "Perf: Window topn optimisation (#21479)"

This reverts commit 936db37.

Author: mbutrovich

benchmarks/queries/h2o/window.sql

@@ -109,11 +109,4 @@ SELECT
     id3,
     v2,
     sum(v2) OVER (PARTITION BY id2 ORDER BY v2 RANGE BETWEEN 3 PRECEDING AND CURRENT ROW) AS my_range_between_by_id2
-FROM large;
-
--- Window Top-N (ROW_NUMBER top-2 per partition)
-SELECT id2, largest2_v2 FROM (
-    SELECT id2, v2 AS largest2_v2,
-           ROW_NUMBER() OVER (PARTITION BY id2 ORDER BY v2 DESC) AS order_v2
-    FROM large WHERE v2 IS NOT NULL
-) sub_query WHERE order_v2 <= 2;
+FROM large;

datafusion/common/src/config.rs

@@ -1087,15 +1087,6 @@ config_namespace! {
         /// past window functions, if possible
         pub enable_window_limits: bool, default = true
 
-        /// When set to true, the optimizer will replace
-        /// Filter(rn<=K) → Window(ROW_NUMBER) → Sort patterns with a
-        /// PartitionedTopKExec that maintains per-partition heaps, avoiding
-        /// a full sort of the input.
-        /// When the window partition key has low cardinality, enabling this optimization
-        /// can improve performance. However, for high cardinality keys, it may
-        /// cause regressions in both memory usage and runtime.
-        pub enable_window_topn: bool, default = false
-
         /// When set to true, the optimizer will push TopK (Sort with fetch)
         /// below hash repartition when the partition key is a prefix of the
         /// sort key, reducing data volume before the shuffle.

datafusion/core/tests/physical_optimizer/mod.rs

@@ -37,6 +37,5 @@ mod sanity_checker;
 #[expect(clippy::needless_pass_by_value)]
 mod test_utils;
 mod window_optimize;
-mod window_topn;
 
 mod pushdown_utils;