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# Command Building Utilities
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YARN-specific utilities for building container launch commands and managing Spark distribution. These utilities handle the low-level details of container command construction and environment setup.
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## Capabilities
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### YarnSparkHadoopUtil
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Utility object providing YARN-specific Hadoop integration and environment management.
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```scala { .api }
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object YarnSparkHadoopUtil {
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  def addPathToEnvironment(env: HashMap[String, String], key: String, value: String): Unit
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  val MEMORY_OVERHEAD_FACTOR: Double
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  val MEMORY_OVERHEAD_MIN: Long
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  val RM_REQUEST_PRIORITY: Priority
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}
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```
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**Environment Management:**
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**`addPathToEnvironment(env, key, value): Unit`**
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- Adds a path value to an environment variable
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- Handles path separator logic for cross-platform compatibility
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- Used for setting up executor environment variables
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**Usage Example:**
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```scala
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import org.apache.spark.deploy.yarn.YarnSparkHadoopUtil
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import scala.collection.mutable.HashMap
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val env = new HashMap[String, String]()
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// Add to PATH environment variable
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YarnSparkHadoopUtil.addPathToEnvironment(env, "PATH", "/usr/local/bin")
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YarnSparkHadoopUtil.addPathToEnvironment(env, "PATH", "/opt/spark/bin")
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// Add to LD_LIBRARY_PATH
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YarnSparkHadoopUtil.addPathToEnvironment(env, "LD_LIBRARY_PATH", "/usr/local/lib")
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println(env("PATH"))  // /usr/local/bin:/opt/spark/bin:$PATH
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```
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**Constants:**
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**`MEMORY_OVERHEAD_FACTOR: Double`**
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- Default memory overhead factor for container memory calculation
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- Typically 0.1 (10% of executor memory)
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- Used when explicit overhead is not specified
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**`MEMORY_OVERHEAD_MIN: Long`**
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- Minimum memory overhead in bytes
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- Typically 384MB (384 * 1024 * 1024 bytes)
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- Ensures adequate overhead for small executor containers
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**`RM_REQUEST_PRIORITY: Priority`**
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- Standard priority for ResourceManager container requests
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- Consistent priority level for all Spark container requests
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- Used by YarnAllocator for container allocation
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**Memory Calculation Example:**
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```scala
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import org.apache.spark.deploy.yarn.YarnSparkHadoopUtil
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def calculateContainerMemory(executorMemoryMB: Long): Long = {
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  val overheadMB = math.max(
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    (executorMemoryMB * YarnSparkHadoopUtil.MEMORY_OVERHEAD_FACTOR).toLong,
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    YarnSparkHadoopUtil.MEMORY_OVERHEAD_MIN / (1024 * 1024)
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  )
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  executorMemoryMB + overheadMB
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}
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// Example calculations
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println(calculateContainerMemory(1024))  // 1408MB (1024 + 384 min overhead)
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println(calculateContainerMemory(8192))  // 9011MB (8192 + 819 calculated overhead)
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```
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### YarnCommandBuilderUtils
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Utilities for building and formatting container launch commands on YARN.
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```scala { .api }
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object YarnCommandBuilderUtils {
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  def quoteForBatchScript(arg: String): String
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  def findJarsDir(sparkHome: String): String
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}
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```
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**Command Building:**
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**`quoteForBatchScript(arg: String): String`**
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- Properly quotes arguments for batch script execution
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- Handles special characters and spaces in arguments
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- Platform-aware quoting for Windows and Unix systems
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**`findJarsDir(sparkHome: String): String`**
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- Locates the jars directory within a Spark installation
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- Handles different Spark distribution layouts
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- Returns path to directory containing Spark JAR files
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**Usage Examples:**
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**Argument Quoting:**
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```scala
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import org.apache.spark.launcher.YarnCommandBuilderUtils
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// Quote arguments with spaces or special characters
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val arg1 = YarnCommandBuilderUtils.quoteForBatchScript("my app name")
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val arg2 = YarnCommandBuilderUtils.quoteForBatchScript("--conf spark.sql.warehouse.dir=/path/with spaces")
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val arg3 = YarnCommandBuilderUtils.quoteForBatchScript("value_with_$_symbol")
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println(arg1)  // "my app name" (on Unix/Linux)
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println(arg2)  // "--conf spark.sql.warehouse.dir=/path/with spaces"
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println(arg3)  // "value_with_\$_symbol" (escaped special chars)
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```
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**JAR Directory Discovery:**
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```scala
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import org.apache.spark.launcher.YarnCommandBuilderUtils
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// Find JAR directory in Spark installation
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val sparkHome = "/opt/spark"
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val jarsDir = YarnCommandBuilderUtils.findJarsDir(sparkHome)
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println(jarsDir)  // /opt/spark/jars (for standard distribution)
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// Use in classpath construction
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val sparkJars = new File(jarsDir).listFiles()
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  .filter(_.getName.endsWith(".jar"))
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  .map(_.getAbsolutePath)
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  .mkString(":")
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```
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## Integration with Container Launch
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### Environment Setup
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```scala
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// Example of environment preparation for executor containers
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def prepareExecutorEnvironment(
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    sparkHome: String, 
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    executorMemory: String,
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    additionalPaths: Seq[String]): HashMap[String, String] = {
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  val env = new HashMap[String, String]()
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  // Set SPARK_HOME
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  env("SPARK_HOME") = sparkHome
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  // Add Spark bins to PATH
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  YarnSparkHadoopUtil.addPathToEnvironment(env, "PATH", s"$sparkHome/bin")
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  YarnSparkHadoopUtil.addPathToEnvironment(env, "PATH", s"$sparkHome/sbin")
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  // Add additional paths
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  additionalPaths.foreach { path =>
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    YarnSparkHadoopUtil.addPathToEnvironment(env, "PATH", path)
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  }
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  // Set Java library path
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  val jarsDir = YarnCommandBuilderUtils.findJarsDir(sparkHome)
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  YarnSparkHadoopUtil.addPathToEnvironment(env, "LD_LIBRARY_PATH", s"$jarsDir/../lib")
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  env
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}
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```
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### Command Construction  
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```scala
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// Example of building executor launch command
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def buildExecutorCommand(
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    sparkHome: String,
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    executorMemory: String, 
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    executorCores: Int,
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    userArgs: Seq[String]): Seq[String] = {
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  val jarsDir = YarnCommandBuilderUtils.findJarsDir(sparkHome)
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  val sparkJars = s"$jarsDir/*"
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  val baseCommand = Seq(
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    "java",
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    s"-Xmx$executorMemory",
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    "-cp", sparkJars,
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    "org.apache.spark.executor.YarnCoarseGrainedExecutorBackend"
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  )
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  // Quote user arguments that might contain spaces
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  val quotedUserArgs = userArgs.map(YarnCommandBuilderUtils.quoteForBatchScript)
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  baseCommand ++ quotedUserArgs
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}
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```
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## Error Handling
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### Path Resolution Errors
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```scala
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try {
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  val jarsDir = YarnCommandBuilderUtils.findJarsDir(sparkHome)
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  // Use jarsDir...
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} catch {
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  case e: IllegalArgumentException =>
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    throw new SparkException(s"Unable to find Spark jars directory in: $sparkHome", e)
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  case e: SecurityException =>
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    throw new SparkException(s"Access denied reading Spark installation: $sparkHome", e)
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}
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```
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### Environment Variable Conflicts
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```scala
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def validateEnvironment(env: HashMap[String, String]): Unit = {
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  // Check for conflicting PATH entries
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  val pathValue = env.getOrElse("PATH", "")
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  if (pathValue.contains("::")) {
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    logWarning("Empty path component detected in PATH environment variable")
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  }
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  // Validate SPARK_HOME consistency
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  val sparkHome = env.get("SPARK_HOME")
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  val pathContainsSparkBin = pathValue.contains("/bin") || pathValue.contains("/sbin")
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  if (sparkHome.isDefined && !pathContainsSparkBin) {
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    logWarning("SPARK_HOME set but Spark binaries may not be in PATH")
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  }
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}
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```
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## Platform Considerations
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### Windows Compatibility
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```scala
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// Platform-specific behavior in YarnCommandBuilderUtils.quoteForBatchScript
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def quoteForPlatform(arg: String): String = {
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  val isWindows = System.getProperty("os.name").toLowerCase.contains("windows")
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  if (isWindows) {
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    // Windows batch script quoting
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    if (arg.contains(" ") || arg.contains("&") || arg.contains("|")) {
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      s""""$arg""""
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    } else {
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      arg
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    }
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  } else {
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    // Unix shell quoting
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    if (arg.contains(" ") || arg.contains("$") || arg.contains("'")) {
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      s"'${arg.replace("'", "'\\''")}'"
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    } else {
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      arg
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    }
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  }
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}
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```
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### Container Resource Constraints
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```scala
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// Memory overhead calculation considering container limits
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def calculateOptimalOverhead(
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    executorMemoryMB: Long,
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    nodeMemoryMB: Long,
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    executorsPerNode: Int): Long = {
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  val standardOverhead = math.max(
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    (executorMemoryMB * YarnSparkHadoopUtil.MEMORY_OVERHEAD_FACTOR).toLong,
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    YarnSparkHadoopUtil.MEMORY_OVERHEAD_MIN / (1024 * 1024)
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  )
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  val totalRequestedMemory = (executorMemoryMB + standardOverhead) * executorsPerNode
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  if (totalRequestedMemory > nodeMemoryMB * 0.9) {
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    // Reduce overhead if total memory exceeds 90% of node capacity
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    val maxOverhead = (nodeMemoryMB * 0.9 / executorsPerNode - executorMemoryMB).toLong
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    math.max(maxOverhead, YarnSparkHadoopUtil.MEMORY_OVERHEAD_MIN / (1024 * 1024))
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  } else {
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    standardOverhead
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  }
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}
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```