[SPARK-17350][SQL] Disable default use of KryoSerializer in Thrift Se…

…rver

In SPARK-4761 / apache#3621 (December 2014) we enabled Kryo serialization by default in the Spark Thrift Server. However, I don't think that the original rationale for doing this still holds now that most Spark SQL serialization is now performed via encoders and our UnsafeRow format.

In addition, the use of Kryo as the default serializer can introduce performance problems because the creation of new KryoSerializer instances is expensive and we haven't performed instance-reuse optimizations in several code paths (including DirectTaskResult deserialization).

Given all of this, I propose to revert back to using JavaSerializer as the default serializer in the Thrift Server.

/cc liancheng

Author: Josh Rosen <joshrosen@databricks.com>

Closes apache#14906 from JoshRosen/disable-kryo-in-thriftserver.

docs/configuration.md

@@ -767,7 +767,7 @@ Apart from these, the following properties are also available, and may be useful
 </tr>
 <tr>
   <td><code>spark.kryo.referenceTracking</code></td>
-  <td>true (false when using Spark SQL Thrift Server)</td>
+  <td>true</td>
   <td>
     Whether to track references to the same object when serializing data with Kryo, which is
     necessary if your object graphs have loops and useful for efficiency if they contain multiple
@@ -838,8 +838,7 @@ Apart from these, the following properties are also available, and may be useful
 <tr>
   <td><code>spark.serializer</code></td>
   <td>
-    org.apache.spark.serializer.<br />JavaSerializer (org.apache.spark.serializer.<br />
-    KryoSerializer when using Spark SQL Thrift Server)
+    org.apache.spark.serializer.<br />JavaSerializer
   </td>
   <td>
     Class to use for serializing objects that will be sent over the network or need to be cached

sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkSQLEnv.scala

@@ -19,8 +19,6 @@ package org.apache.spark.sql.hive.thriftserver
 
 import java.io.PrintStream
 
-import scala.collection.JavaConverters._
-
 import org.apache.spark.{SparkConf, SparkContext}
 import org.apache.spark.internal.Logging
 import org.apache.spark.sql.{SparkSession, SQLContext}
@@ -37,8 +35,6 @@ private[hive] object SparkSQLEnv extends Logging {
   def init() {
     if (sqlContext == null) {
       val sparkConf = new SparkConf(loadDefaults = true)
-      val maybeSerializer = sparkConf.getOption("spark.serializer")
-      val maybeKryoReferenceTracking = sparkConf.getOption("spark.kryo.referenceTracking")
       // If user doesn't specify the appName, we want to get [SparkSQL::localHostName] instead of
       // the default appName [SparkSQLCLIDriver] in cli or beeline.
       val maybeAppName = sparkConf
@@ -47,12 +43,6 @@ private[hive] object SparkSQLEnv extends Logging {
 
       sparkConf
         .setAppName(maybeAppName.getOrElse(s"SparkSQL::${Utils.localHostName()}"))
-        .set(
-          "spark.serializer",
-          maybeSerializer.getOrElse("org.apache.spark.serializer.KryoSerializer"))
-        .set(
-          "spark.kryo.referenceTracking",
-          maybeKryoReferenceTracking.getOrElse("false"))
 
       val sparkSession = SparkSession.builder.config(sparkConf).enableHiveSupport().getOrCreate()
       sparkContext = sparkSession.sparkContext