[SPARK-2087] [SQL] Multiple thriftserver sessions with single HiveContext instance

Still, we keep only a single HiveContext within ThriftServer, and we also create a object called `SQLSession` for isolating the different user states.

Developers can obtain/release a new user session via `openSession` and `closeSession`, and `SQLContext` and `HiveContext` will also provide a default session if no `openSession` called, for backward-compatibility.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #4885 from chenghao-intel/multisessions_singlecontext and squashes the following commits:

1c47b2a [Cheng Hao] rename the tss => tlSession
815b27a [Cheng Hao] code style issue
57e3fa0 [Cheng Hao] openSession is not compatible between Hive0.12 & 0.13.1
4665b0d [Cheng Hao] thriftservice with single context

2 files changed, 54 insertions, 6 deletions

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 9c49e84bf9..297d0d644a 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
@@ -63,8 +63,10 @@ class SQLContext(@transient val sparkContext: SparkContext)
 
   def this(sparkContext: JavaSparkContext) = this(sparkContext.sc)
 
-  // Note that this is a lazy val so we can override the default value in subclasses.
-  protected[sql] lazy val conf: SQLConf = new SQLConf
+  /**
+   * @return Spark SQL configuration
+   */
+  protected[sql] def conf = tlSession.get().conf
 
   /**
    * Set Spark SQL configuration properties.
@@ -103,9 +105,11 @@ class SQLContext(@transient val sparkContext: SparkContext)
    */
   def getAllConfs: immutable.Map[String, String] = conf.getAllConfs
 
+  // TODO how to handle the temp table per user session?
   @transient
   protected[sql] lazy val catalog: Catalog = new SimpleCatalog(true)
 
+  // TODO how to handle the temp function per user session?
   @transient
   protected[sql] lazy val functionRegistry: FunctionRegistry = new SimpleFunctionRegistry(true)
 
@@ -138,6 +142,14 @@ class SQLContext(@transient val sparkContext: SparkContext)
 
   protected[sql] def executePlan(plan: LogicalPlan) = new this.QueryExecution(plan)
 
+  @transient
+  protected[sql] val tlSession = new ThreadLocal[SQLSession]() {
+    override def initialValue = defaultSession
+  }
+
+  @transient
+  protected[sql] val defaultSession = createSession()
+
   sparkContext.getConf.getAll.foreach {
     case (key, value) if key.startsWith("spark.sql") => setConf(key, value)
     case _ =>
@@ -194,6 +206,7 @@ class SQLContext(@transient val sparkContext: SparkContext)
    * }}}
    *
    * @group basic
+   * TODO move to SQLSession?
    */
   @transient
   val udf: UDFRegistration = new UDFRegistration(this)
@@ -1059,6 +1072,32 @@ class SQLContext(@transient val sparkContext: SparkContext)
     )
   }
 
+
+  protected[sql] def openSession(): SQLSession = {
+    detachSession()
+    val session = createSession()
+    tlSession.set(session)
+
+    session
+  }
+
+  protected[sql] def currentSession(): SQLSession = {
+    tlSession.get()
+  }
+
+  protected[sql] def createSession(): SQLSession = {
+    new this.SQLSession()
+  }
+
+  protected[sql] def detachSession(): Unit = {
+    tlSession.remove()
+  }
+
+  protected[sql] class SQLSession {
+    // Note that this is a lazy val so we can override the default value in subclasses.
+    protected[sql] lazy val conf: SQLConf = new SQLConf
+  }
+
   /**
    * :: DeveloperApi ::
    * The primary workflow for executing relational queries using Spark.  Designed to allow easy
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/test/TestSQLContext.scala b/sql/core/src/main/scala/org/apache/spark/sql/test/TestSQLContext.scala
index 4e1ec38bd0..356a6100d2 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/test/TestSQLContext.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/test/TestSQLContext.scala
@@ -24,16 +24,22 @@ import org.apache.spark.sql.{DataFrame, SQLConf, SQLContext}
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
 
 /** A SQLContext that can be used for local testing. */
-object TestSQLContext
+class LocalSQLContext
   extends SQLContext(
     new SparkContext(
       "local[2]",
       "TestSQLContext",
       new SparkConf().set("spark.sql.testkey", "true"))) {
 
-  /** Fewer partitions to speed up testing. */
-  protected[sql] override lazy val conf: SQLConf = new SQLConf {
-    override def numShufflePartitions: Int = this.getConf(SQLConf.SHUFFLE_PARTITIONS, "5").toInt
+  override protected[sql] def createSession(): SQLSession = {
+    new this.SQLSession()
+  }
+
+  protected[sql] class SQLSession extends super.SQLSession {
+    protected[sql] override lazy val conf: SQLConf = new SQLConf {
+      /** Fewer partitions to speed up testing. */
+      override def numShufflePartitions: Int = this.getConf(SQLConf.SHUFFLE_PARTITIONS, "5").toInt
+    }
   }
 
   /**
@@ -45,3 +51,6 @@ object TestSQLContext
   }
 
 }
+
+object TestSQLContext extends LocalSQLContext
+