From 732cf9e85fcd58e3a1e6962783550c0438700225 Mon Sep 17 00:00:00 2001
From: Sital Kedia <skedia@fb.com>
Date: Fri, 2 Feb 2018 16:05:34 -0800
Subject: [PATCH] [SPARK-21113][CORE] Turn off read ahead input stream for
 unshafe shuffle reader

---
 .../util/collection/unsafe/sort/UnsafeSorterSpillReader.java  | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
index e2f48e5508af6..71e7c7a95ebdb 100644
--- a/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
+++ b/core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeSorterSpillReader.java
@@ -76,8 +76,10 @@ public UnsafeSorterSpillReader(
         SparkEnv.get() == null ? 0.5 :
              SparkEnv.get().conf().getDouble("spark.unsafe.sorter.spill.read.ahead.fraction", 0.5);
 
+    // SPARK-23310: Disable read-ahead input stream, because it is causing lock contention and perf regression for
+    // TPC-DS queries.
     final boolean readAheadEnabled = SparkEnv.get() != null &&
-        SparkEnv.get().conf().getBoolean("spark.unsafe.sorter.spill.read.ahead.enabled", true);
+        SparkEnv.get().conf().getBoolean("spark.unsafe.sorter.spill.read.ahead.enabled", false);
 
     final InputStream bs =
         new NioBufferedFileInputStream(file, (int) bufferSizeBytes);