diff --git a/sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/SQLConf.scala
similarity index 53%
rename from sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala
rename to sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/SQLConf.scala
index df76195723071..c78c2439c2533 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/SQLConf.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/planning/SQLConf.scala
@@ -15,23 +15,34 @@
  * limitations under the License.
  */
 
-package org.apache.spark.sql
+package org.apache.spark.sql.catalyst.planning
 
 import java.util.Properties
 
 import scala.collection.JavaConverters._
 
+private object SQLConf {
+  @transient protected[spark] val confSettings = java.util.Collections.synchronizedMap(
+    new java.util.HashMap[String, String]())
+}
+
 /**
- * SQLConf holds mutable config parameters and hints.  These can be set and
- * queried either by passing SET commands into Spark SQL's DSL
- * functions (sql(), hql(), etc.), or by programmatically using setters and
- * getters of this class.
+ * A trait that enables the setting and getting of mutable config parameters/hints. The central
+ * location for storing them is uniquely located in the same-name private companion object.
+ * Therefore, all classes that mix in this trait share all the hints.
+ *
+ * In the presence of a SQLContext, these can be set and queried either by passing SET commands
+ * into Spark SQL's DSL functions (sql(), hql(), etc.). Otherwise, users of this trait can
+ * modify the hints by programmatically calling the setters and getters of this trait.
  *
  * SQLConf is thread-safe (internally synchronized so safe to be used in multiple threads).
  */
 trait SQLConf {
   import SQLConf._
 
+  import SQLConf._
+  protected[spark] val settings = confSettings
+
   /** ************************ Spark SQL Params/Hints ******************* */
   // TODO: refactor so that these hints accessors don't pollute the name space of SQLContext?
 
@@ -40,50 +51,58 @@ trait SQLConf {
 
   /**
    * Upper bound on the sizes (in bytes) of the tables qualified for the auto conversion to
-   * a broadcast value during the physical executions of join operations.  Setting this to 0
+   * a broadcast value during the physical executions of join operations.  Setting this to -1
    * effectively disables auto conversion.
-   * Hive setting: hive.auto.convert.join.noconditionaltask.size.
+   *
+   * Hive setting: hive.auto.convert.join.noconditionaltask.size, whose default value is also 10000.
    */
   private[spark] def autoConvertJoinSize: Int = get(AUTO_CONVERT_JOIN_SIZE, "10000").toInt
 
-  /** ********************** SQLConf functionality methods ************ */
+  /**
+   * The default size in bytes to assign to a logical operator's estimation statistics.  By default,
+   * it is set to a larger value than `autoConvertJoinSize`, hence any logical operator without a
+   * properly implemented estimation of this statistic will not be incorrectly broadcasted in joins.
+   */
+  private[spark] def statsDefaultSizeInBytes: Long =
+    getOption("spark.sql.catalyst.stats.sizeInBytes").map(_.toLong)
+      .getOrElse(autoConvertJoinSize + 1)
 
-  @transient
-  private val settings = java.util.Collections.synchronizedMap(
-    new java.util.HashMap[String, String]())
+  /** ********************** SQLConf functionality methods ************ */
 
   def set(props: Properties): Unit = {
-    props.asScala.foreach { case (k, v) => this.settings.put(k, v) }
+    confSettings.synchronized {
+      props.asScala.foreach { case (k, v) => confSettings.put(k, v) }
+    }
   }
 
   def set(key: String, value: String): Unit = {
     require(key != null, "key cannot be null")
-    require(value != null, s"value cannot be null for $key")
-    settings.put(key, value)
+    require(value != null, s"value cannot be null for key: $key")
+    confSettings.put(key, value)
   }
 
   def get(key: String): String = {
-    Option(settings.get(key)).getOrElse(throw new NoSuchElementException(key))
+    Option(confSettings.get(key)).getOrElse(throw new NoSuchElementException(key))
   }
 
   def get(key: String, defaultValue: String): String = {
-    Option(settings.get(key)).getOrElse(defaultValue)
+    Option(confSettings.get(key)).getOrElse(defaultValue)
   }
 
-  def getAll: Array[(String, String)] = settings.synchronized { settings.asScala.toArray }
+  def getAll: Array[(String, String)] = confSettings.synchronized { confSettings.asScala.toArray }
 
-  def getOption(key: String): Option[String] = Option(settings.get(key))
+  def getOption(key: String): Option[String] = Option(confSettings.get(key))
 
-  def contains(key: String): Boolean = settings.containsKey(key)
+  def contains(key: String): Boolean = confSettings.containsKey(key)
 
   def toDebugString: String = {
-    settings.synchronized {
-      settings.asScala.toArray.sorted.map{ case (k, v) => s"$k=$v" }.mkString("\n")
+    confSettings.synchronized {
+      confSettings.asScala.toArray.sorted.map{ case (k, v) => s"$k=$v" }.mkString("\n")
     }
   }
 
   private[spark] def clear() {
-    settings.clear()
+    confSettings.clear()
   }
 
 }
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
index 3ac9b8d8e42ef..45e8830b9ba76 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala
@@ -19,17 +19,24 @@ package org.apache.spark.sql.catalyst.plans.logical
 
 import org.apache.spark.sql.catalyst.errors.TreeNodeException
 import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.planning.SQLConf
 import org.apache.spark.sql.catalyst.plans.QueryPlan
 import org.apache.spark.sql.catalyst.types.StructType
 import org.apache.spark.sql.catalyst.trees
 
-abstract class LogicalPlan extends QueryPlan[LogicalPlan] {
+abstract class LogicalPlan extends QueryPlan[LogicalPlan] with SQLConf {
   self: Product =>
 
+  // TODO: make a case class?
   protected class Statistics {
     lazy val childrenStats = children.map(_.statistics)
+
     lazy val numTuples: Long = childrenStats.map(_.numTuples).sum
-    lazy val sizeInBytes: Long = childrenStats.map(_.sizeInBytes).sum
+
+    lazy val sizeInBytes: Long = {
+      val sum = childrenStats.map(_.sizeInBytes).sum
+      if (sum == 0) statsDefaultSizeInBytes else sum
+    }
   }
 
   /**
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
index 568a64951def3..d3718c55543fb 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
@@ -17,6 +17,7 @@
 
 package org.apache.spark.sql
 
+
 import scala.language.implicitConversions
 import scala.reflect.runtime.universe.TypeTag
 
@@ -24,14 +25,15 @@ import org.apache.hadoop.conf.Configuration
 
 import org.apache.spark.annotation.{AlphaComponent, DeveloperApi, Experimental}
 import org.apache.spark.rdd.RDD
-import org.apache.spark.sql.catalyst.analysis._
 import org.apache.spark.sql.catalyst.ScalaReflection
-import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.analysis._
 import org.apache.spark.sql.catalyst.dsl.ExpressionConversions
-import org.apache.spark.sql.catalyst.types._
+import org.apache.spark.sql.catalyst.expressions._
 import org.apache.spark.sql.catalyst.optimizer.Optimizer
+import org.apache.spark.sql.catalyst.planning.SQLConf
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 import org.apache.spark.sql.catalyst.rules.RuleExecutor
+import org.apache.spark.sql.catalyst.types._
 import org.apache.spark.sql.columnar.InMemoryRelation
 import org.apache.spark.sql.execution._
 import org.apache.spark.sql.execution.SparkStrategies
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
index bafc5aaff3f03..dffa112fb7ee2 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/SparkStrategies.scala
@@ -82,6 +82,7 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
         if left.statistics.sizeInBytes <= sqlContext.autoConvertJoinSize =>
           broadcastHashJoin(leftKeys, rightKeys, left, right, condition, BuildLeft)
 
+      // TODO: use optimization here as well
       case ExtractEquiJoinKeys(Inner, leftKeys, rightKeys, condition, left, right) =>
         val hashJoin =
           execution.ShuffledHashJoin(