[SPARK-23312][SQL] add a config to turn off vectorized cache reader

## What changes were proposed in this pull request?

https://issues.apache.org/jira/browse/SPARK-23309 reported a performance regression about cached table in Spark 2.3. While the investigating is still going on, this PR adds a conf to turn off the vectorized cache reader, to unblock the 2.3 release.

## How was this patch tested?

a new test

Author: Wenchen Fan <wenchen@databricks.com>

Closes #20483 from cloud-fan/cache.

Author: cloud-fan

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -141,6 +141,12 @@ object SQLConf {
       .booleanConf
       .createWithDefault(true)
 
+  val CACHE_VECTORIZED_READER_ENABLED =
+    buildConf("spark.sql.inMemoryColumnarStorage.enableVectorizedReader")
+      .doc("Enables vectorized reader for columnar caching.")
+      .booleanConf
+      .createWithDefault(true)
+
   val COLUMN_VECTOR_OFFHEAP_ENABLED =
     buildConf("spark.sql.columnVector.offheap.enabled")
       .internal()
@@ -1272,6 +1278,8 @@ class SQLConf extends Serializable with Logging {
 
   def columnBatchSize: Int = getConf(COLUMN_BATCH_SIZE)
 
+  def cacheVectorizedReaderEnabled: Boolean = getConf(CACHE_VECTORIZED_READER_ENABLED)
+
   def numShufflePartitions: Int = getConf(SHUFFLE_PARTITIONS)
 
   def targetPostShuffleInputSize: Long =

sql/core/src/main/scala/org/apache/spark/sql/execution/columnar/InMemoryTableScanExec.scala

@@ -54,7 +54,7 @@ case class InMemoryTableScanExec(
   override val supportsBatch: Boolean = {
     // In the initial implementation, for ease of review
     // support only primitive data types and # of fields is less than wholeStageMaxNumFields
-    relation.schema.fields.forall(f => f.dataType match {
+    conf.cacheVectorizedReaderEnabled && relation.schema.fields.forall(f => f.dataType match {
       case BooleanType | ByteType | ShortType | IntegerType | LongType |
            FloatType | DoubleType => true
       case _ => false

sql/core/src/test/scala/org/apache/spark/sql/CachedTableSuite.scala

@@ -21,15 +21,14 @@ import scala.collection.mutable.HashSet
 import scala.concurrent.duration._
 import scala.language.postfixOps
 
-import org.scalatest.concurrent.Eventually._
-
 import org.apache.spark.CleanerListener
 import org.apache.spark.sql.catalyst.TableIdentifier
 import org.apache.spark.sql.catalyst.expressions.SubqueryExpression
 import org.apache.spark.sql.execution.{RDDScanExec, SparkPlan}
 import org.apache.spark.sql.execution.columnar._
 import org.apache.spark.sql.execution.exchange.ShuffleExchangeExec
 import org.apache.spark.sql.functions._
+import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.test.{SharedSQLContext, SQLTestUtils}
 import org.apache.spark.storage.{RDDBlockId, StorageLevel}
 import org.apache.spark.util.{AccumulatorContext, Utils}
@@ -782,4 +781,16 @@ class CachedTableSuite extends QueryTest with SQLTestUtils with SharedSQLContext
       assert(getNumInMemoryRelations(cachedDs2) == 1)
     }
   }
+
+  test("SPARK-23312: vectorized cache reader can be disabled") {
+    Seq(true, false).foreach { vectorized =>
+      withSQLConf(SQLConf.CACHE_VECTORIZED_READER_ENABLED.key -> vectorized.toString) {
+        val df = spark.range(10).cache()
+        df.queryExecution.executedPlan.foreach {
+          case i: InMemoryTableScanExec => assert(i.supportsBatch == vectorized)
+          case _ =>
+        }
+      }
+    }
+  }
 }