From 398a891cd31dd9c275717f5f37d509dec9f2de64 Mon Sep 17 00:00:00 2001
From: Yuanjian Li <xyliyuanjian@gmail.com>
Date: Mon, 19 Aug 2019 22:44:41 +0800
Subject: [PATCH] More comments

---
 .../spark/sql/execution/exchange/ShuffleExchangeExec.scala    | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/ShuffleExchangeExec.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/ShuffleExchangeExec.scala
index b83de0e39fb6d..02f7b419bd7fc 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/ShuffleExchangeExec.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/exchange/ShuffleExchangeExec.scala
@@ -264,6 +264,10 @@ object ShuffleExchangeExec {
             prefixComparator,
             prefixComputer,
             pageSize,
+            // As we need to compare the binary of UnsafeRow here, we can't make sure whether all
+            // the fields can sort fully with prefix like SortExec. So we disable radix sort here
+            // to avoid getting unstable sort, and result to a correctness bug.
+            // See more details in SPARK-28699.
             false /* canUseRadixSort */)
           sorter.sort(iter.asInstanceOf[Iterator[UnsafeRow]])
         }