diff --git a/be/src/util/tdigest.h b/be/src/util/tdigest.h
index a58e0bdfd7603a..8314ebeb8a351c 100644
--- a/be/src/util/tdigest.h
+++ b/be/src/util/tdigest.h
@@ -649,6 +649,9 @@ class TDigest {
     // when complete, _unprocessed will be empty and _processed will have at most _max_processed centroids
     void process() {
         CentroidComparator cc;
+        // select percentile_approx(lo_orderkey,0.5) from lineorder;
+        // have test pdqsort and RadixSort, find here pdqsort performance is better when data is struct Centroid
+        // But when sort plain type like int/float of std::vector<T>, find RadixSort is better
         pdqsort(_unprocessed.begin(), _unprocessed.end(), cc);
         auto count = _unprocessed.size();
         _unprocessed.insert(_unprocessed.end(), _processed.cbegin(), _processed.cend());