Merge remote-tracking branch 'origin/issue-16990-percentile-cont' into issue-16990-percentile-cont

# Conflicts:
#	datafusion/functions-aggregate/src/approx_percentile_cont.rs
#	datafusion/functions-aggregate/src/approx_percentile_cont_with_weight.rs

Author: liamzwbao

datafusion/functions-aggregate/src/approx_percentile_cont.rs

@@ -565,4 +565,41 @@ mod tests {
         accumulator.merge_digests(&[t2]);
         assert_eq!(accumulator.digest.count(), 100_000);
     }
+
+    #[test]
+    fn test_merge_digests_preserves_max_size() {
+        // Create accumulator with specific max_size
+        let original_max_size = 200;
+        let mut accumulator = ApproxPercentileAccumulator::new_with_max_size(
+            0.5,
+            DataType::Float64,
+            original_max_size,
+        );
+
+        // Verify initial max_size
+        assert_eq!(accumulator.digest.max_size(), original_max_size);
+
+        // Create new TDigests with different max_size
+        let different_max_size = 50;
+        let mut new_digests: Vec<TDigest> = Vec::new();
+
+        for _ in 1..=5 {
+            let t = TDigest::new(different_max_size);
+            let values: Vec<_> = (1..=1_000).map(f64::from).collect();
+            let t = t.merge_unsorted_f64(values);
+            new_digests.push(t);
+        }
+
+        accumulator.merge_digests(&new_digests);
+        assert_eq!(
+            accumulator.digest.max_size(),
+            original_max_size,
+            "merge_digests should preserve the accumulator's original max_size"
+        );
+        assert_eq!(
+            accumulator.digest.count(),
+            5_000,
+            "Data should have been merged"
+        );
+    }
 }

datafusion/sqllogictest/test_files/aggregate.slt

@@ -1832,7 +1832,7 @@ d 124
 e 115
 
 query TI
-SELECT c1, approx_percentile_cont_with_weight(c2, 0.95) WITHIN GROUP (ORDER BY c3) AS c3_p95 FROM aggregate_test_100 GROUP BY 1 ORDER BY 1
+SELECT c1, approx_percentile_cont_with_weight(c2, 0.95, 200) WITHIN GROUP (ORDER BY c3) AS c3_p95 FROM aggregate_test_100 GROUP BY 1 ORDER BY 1
 ----
 a 74
 b 68