[LIVY-1059] Add livy.spark.yarn.queue configuration to set default YARN queue

conf/livy.conf.template

@@ -47,6 +47,10 @@
 # What spark deploy mode Livy sessions should use.
 # livy.spark.deploy-mode =
 
+# What default YARN queue Livy sessions should use if not specified in the client request.
+# By default, it is null and falls back to the global Hadoop cluster default queue.
+# livy.spark.yarn.queue = default
+
 # Configure Livy server http request and response header size.
 # livy.server.request-header.size = 131072
 # livy.server.response-header.size = 131072

server/src/main/scala/org/apache/livy/LivyConf.scala

@@ -41,6 +41,7 @@ object LivyConf {
 
   val TEST_MODE = ClientConf.TEST_MODE
 
+  val SPARK_YARN_QUEUE = Entry("livy.spark.yarn.queue", null)
   val SPARK_HOME = Entry("livy.server.spark-home", null)
   val LIVY_SPARK_MASTER = Entry("livy.spark.master", "local")
   val LIVY_SPARK_DEPLOY_MODE = Entry("livy.spark.deploy-mode", null)
@@ -485,6 +486,9 @@ class LivyConf(loadDefaults: Boolean) extends ClientConf[LivyConf](null) {
   /** Return the spark master Livy sessions should use. */
   def sparkMaster(): String = get(LIVY_SPARK_MASTER)
 
+  /** Return the value of spark yarn queue. */
+  def getYarnQueue(): Option[String] = Option(get(SPARK_YARN_QUEUE))
+
   /** Return the path to the spark-submit executable. */
   def sparkSubmit(): String = {
     sparkHome().map { _ + File.separator + "bin" + File.separator + "spark-submit" }.get

server/src/main/scala/org/apache/livy/server/batch/BatchSession.scala

@@ -83,7 +83,7 @@ object BatchSession extends Logging {
       request.executorMemory.foreach(builder.executorMemory)
       request.executorCores.foreach(builder.executorCores)
       request.numExecutors.foreach(builder.numExecutors)
-      request.queue.foreach(builder.queue)
+      request.queue.orElse(livyConf.getYarnQueue()).foreach(builder.queue)
       request.name.foreach(builder.name)
 
       sessionStore.save(BatchSession.RECOVERY_SESSION_TYPE, s.recoveryMetadata)
@@ -120,6 +120,7 @@ object BatchSession extends Logging {
       owner,
       impersonatedUser,
       sessionStore,
+      request.queue.orElse(livyConf.getYarnQueue()),
       mockApp.map { m => (_: BatchSession) => m }.getOrElse(createSparkApp))
   }
 
@@ -137,6 +138,7 @@ object BatchSession extends Logging {
       m.owner,
       m.proxyUser,
       sessionStore,
+      None,
       mockApp.map { m => (_: BatchSession) => m }.getOrElse { s =>
         SparkApp.create(m.appTag, m.appId, None, livyConf, Option(s))
       })
@@ -152,6 +154,7 @@ class BatchSession(
     owner: String,
     override val proxyUser: Option[String],
     sessionStore: SessionStore,
+    val queue: Option[String],
     sparkApp: BatchSession => SparkApp)
   extends Session(id, name, owner, livyConf) with SparkAppListener {
   import BatchSession._

server/src/main/scala/org/apache/livy/server/interactive/InteractiveSession.scala

@@ -107,7 +107,7 @@ object InteractiveSession extends Logging {
         SparkLauncher.EXECUTOR_MEMORY -> request.executorMemory.map(_.toString),
         "spark.executor.instances" -> request.numExecutors.map(_.toString),
         "spark.app.name" -> request.name.map(_.toString),
-        "spark.yarn.queue" -> request.queue
+        "spark.yarn.queue" -> request.queue.orElse(livyConf.getYarnQueue())
       )
 
       userOpts.foreach { case (key, opt) =>
@@ -152,7 +152,7 @@ object InteractiveSession extends Logging {
       request.jars,
       request.numExecutors,
       request.pyFiles,
-      request.queue,
+      request.queue.orElse(livyConf.getYarnQueue()),
       mockApp)
   }
 

server/src/test/scala/org/apache/livy/server/batch/BatchSessionSpec.scala

@@ -138,6 +138,65 @@ class BatchSessionSpec
       }) should be (true)
     }
 
+    it("should inherit the default YARN queue from LivyConf when request queue is empty") {
+      val req = new CreateBatchRequest()
+      req.file = script.toString
+      req.queue = None // Explicitly empty
+      req.conf = Map("spark.driver.extraClassPath" -> sys.props("java.class.path"))
+
+      // Set default queue in LivyConf configuration
+      val conf = new LivyConf()
+        .set(LivyConf.LOCAL_FS_WHITELIST, sys.props("java.io.tmpdir"))
+        .set(LivyConf.SPARK_YARN_QUEUE, "livy-default-batch-queue")
+
+      val accessManager = new AccessManager(conf)
+      val mockApp = mock[SparkApp]
+
+      val batch = BatchSession.create(
+        id = 10,
+        name = None,
+        request = req,
+        livyConf = conf,
+        accessManager = accessManager,
+        owner = null,
+        proxyUser = None,
+        sessionStore = sessionStore,
+        mockApp = Some(mockApp)
+      )
+
+      // Verify that the batch session structure captured the fallback queue configuration
+      batch.queue shouldBe Some("livy-default-batch-queue")
+    }
+
+    it("should prioritize user-specified request queue over LivyConf configuration") {
+      val req = new CreateBatchRequest()
+      req.file = script.toString
+      req.queue = Some("user-custom-batch-queue") // Explicitly requested by user
+      req.conf = Map("spark.driver.extraClassPath" -> sys.props("java.class.path"))
+
+      val conf = new LivyConf()
+        .set(LivyConf.LOCAL_FS_WHITELIST, sys.props("java.io.tmpdir"))
+        .set(LivyConf.SPARK_YARN_QUEUE, "livy-default-batch-queue")
+
+      val accessManager = new AccessManager(conf)
+      val mockApp = mock[SparkApp]
+
+      val batch = BatchSession.create(
+        id = 20,
+        name = None,
+        request = req,
+        livyConf = conf,
+        accessManager = accessManager,
+        owner = null,
+        proxyUser = None,
+        sessionStore = sessionStore,
+        mockApp = Some(mockApp)
+      )
+
+      // Verify user context takes absolute priority over fallback definition
+      batch.queue shouldBe Some("user-custom-batch-queue")
+    }
+
     def testRecoverSession(name: Option[String]): Unit = {
       val conf = new LivyConf()
       val req = new CreateBatchRequest()

server/src/test/scala/org/apache/livy/server/interactive/InteractiveSessionSpec.scala

@@ -322,4 +322,71 @@ class InteractiveSessionSpec extends FunSpec
       s.logLines().mkString should include("RSCDriver URI is unknown")
     }
   }
+
+  describe("InteractiveSession") {
+    it("should inherit the default YARN queue from LivyConf when request queue is empty") {
+      // Create a clean instance of LivyConf for this isolated check
+      val testLivyConf = new LivyConf()
+        .set(LivyConf.REPL_JARS, "dummy.jar")
+        .set(LivyConf.SPARK_YARN_QUEUE, "livy-default-queue")
+
+      val req = new CreateInteractiveRequest()
+      req.kind = Spark
+      req.queue = None // Explicitly empty
+      req.conf = Map(RSCConf.Entry.LIVY_JARS.key() -> "")
+
+      // Create a mock RSCClient to avoid spawning a real background spark-submit process
+      val mockClient = Some(mock[RSCClient])
+
+      val s = InteractiveSession.create(
+        id = 101,
+        name = None,
+        owner = "systest",
+        proxyUser = None,
+        livyConf = testLivyConf,
+        accessManager = accessManager,
+        request = req,
+        sessionStore = mock[SessionStore],
+        ttl = None,
+        idleTimeout = None,
+        mockApp = None,
+        mockClient = mockClient
+      )
+
+      // Verify that the internal session state correctly holds the fallback queue string
+      s.queue shouldBe Some("livy-default-queue")
+    }
+
+    it("should prioritize user-specified request queue over LivyConf global configuration") {
+      val testLivyConf = new LivyConf()
+        .set(LivyConf.REPL_JARS, "dummy.jar")
+        .set(LivyConf.SPARK_YARN_QUEUE, "livy-default-queue")
+
+      val req = new CreateInteractiveRequest()
+      req.kind = Spark
+      req.queue = Some("user-custom-queue") // Explicitly provided by request
+      req.conf = Map(RSCConf.Entry.LIVY_JARS.key() -> "")
+
+      val mockClient = Some(mock[RSCClient])
+
+      val s = InteractiveSession.create(
+        id = 102,
+        name = None,
+        owner = "systest",
+        proxyUser = None,
+        livyConf = testLivyConf,
+        accessManager = accessManager,
+        request = req,
+        sessionStore = mock[SessionStore],
+        ttl = None,
+        idleTimeout = None,
+        mockApp = None,
+        mockClient = mockClient
+      )
+
+      // Verify that user context takes absolute priority over fallback definitions
+      s.queue shouldBe Some("user-custom-queue")
+    }
+
+  }
 }