fix: Only apply SingleDistinctToGroupBy rewrite when it pays (closes #25932)

datafusion/common/src/config.rs

@@ -1940,6 +1940,21 @@ config_namespace! {
         /// projections or aliases.
         pub enable_unions_to_filter: bool, default = false
 
+        /// When `true`, the `SingleDistinctToGroupBy` optimizer rule keeps a grouped
+        /// DISTINCT aggregate native, instead of rewriting it into a two-phase `GROUP BY`,
+        /// when every DISTINCT argument is a fixed-width, non-float type. This lowers peak
+        /// memory when no memory limit is set, because the intermediate
+        /// `(group, distinct value)` result is never built.
+        ///
+        /// Under a memory limit, the rewrite can spill those pairs, but the native
+        /// accumulator keeps each group's distinct values in memory. With this option
+        /// enabled, a query can need more memory, or fail where the rewrite finishes.
+        ///
+        /// Queries without `GROUP BY`, and other argument types, keep the rewrite.
+        ///
+        /// See <https://github.com/apache/datafusion/issues/25932>
+        pub single_distinct_aggregation_prefer_memory: bool, default = false
+
         /// Prefer native grouped DISTINCT aggregation when target_partitions is 1
         /// and every aggregate explicitly supports a specialized GroupsAccumulator
         /// for its DISTINCT argument types. Defaults to false, preserving the