title: Spark 1.6: java.lang.IllegalArgumentException: spark.sql.execution.id is already set
body: <p>I'm using spark 1.6 and run into the issue above when I run the following code:</p>
  
  <pre><code>// Imports
  import org.apache.spark.sql.hive.HiveContext
  import org.apache.spark.{SparkConf, SparkContext}
  import org.apache.spark.sql.SaveMode
  import scala.concurrent.ExecutionContext.Implicits.global
  import java.util.Properties
  import scala.concurrent.Future
  
  // Set up spark on local with 2 threads
  val conf = new SparkConf().setMaster("local[2]").setAppName("app")
  val sc = new SparkContext(conf)
  val sqlCtx = new HiveContext(sc)
  
  // Create fake dataframe
  import sqlCtx.implicits._
  var df = sc.parallelize(1 to 50000).map { i =&gt; (i, i, i, i, i, i, i) }.toDF("a", "b", "c", "d", "e", "f", "g").repartition(2)
  // Write it as a parquet file
  df.write.parquet("/tmp/parquet1")
  df = sqlCtx.read.parquet("/tmp/parquet1")
  
  // JDBC connection
  val url = s"jdbc:postgresql://localhost:5432/tempdb"
  val prop = new Properties()
  prop.setProperty("user", "admin")
  prop.setProperty("password", "")
  
  // 4 futures - at least one of them has been consistently failing for
  val x1 = Future { df.write.jdbc(url, "temp1", prop) }
  val x2 = Future { df.write.jdbc(url, "temp2", prop) }
  val x3 = Future { df.write.jdbc(url, "temp3", prop) }
  val x4 = Future { df.write.jdbc(url, "temp4", prop) }
  </code></pre>
  
  <p>Here's the github gist: <a href="https://gist.github.com/karanveerm/27d852bf311e39f05491">https://gist.github.com/karanveerm/27d852bf311e39f05491</a></p>
  
  <p>The error I get is:
   at </p>
  
  <pre><code>org.apache.spark.sql.execution.SQLExecution$.withNewExecutionId(SQLExecution.scala:87) ~[org.apache.spark.spark-sql_2.11-1.6.0.jar:1.6.0]
          at org.apache.spark.sql.DataFrame.withNewExecutionId(DataFrame.scala:2125) ~[org.apache.spark.spark-sql_2.11-1.6.0.jar:1.6.0]
          at org.apache.spark.sql.DataFrame.foreachPartition(DataFrame.scala:1482) ~[org.apache.spark.spark-sql_2.11-1.6.0.jar:1.6.0]
          at org.apache.spark.sql.execution.datasources.jdbc.JdbcUtils$.saveTable(JdbcUtils.scala:247) ~[org.apache.spark.spark-sql_2.11-1.6.0.jar:1.6.0]
          at org.apache.spark.sql.DataFrameWriter.jdbc(DataFrameWriter.scala:306) ~[org.apache.spark.spark-sql_2.11-1.6.0.jar:1.6.0]
          at writer.SQLWriter$.writeDf(Writer.scala:75) ~[temple.temple-1.0-sans-externalized.jar:na]
          at writer.Writer$.writeDf(Writer.scala:33) ~[temple.temple-1.0-sans-externalized.jar:na]
          at controllers.Api$$anonfun$downloadTable$1$$anonfun$apply$25.apply(Api.scala:460) ~[temple.temple-1.0-sans-externalized.jar:2.4.6]
          at controllers.Api$$anonfun$downloadTable$1$$anonfun$apply$25.apply(Api.scala:452) ~[temple.temple-1.0-sans-externalized.jar:2.4.6]
          at scala.util.Success$$anonfun$map$1.apply(Try.scala:237) ~[org.scala-lang.scala-library-2.11.7.jar:na]
  </code></pre>
  
  <p>Is this a spark bug or am I doing something wrong / any workarounds?</p>