<!-- Enable MRv1 compatibility -->
<property>
  <name>mapreduce.framework.name</name>
  <value>yarn</value>
</property>
<property>
  <name>mapreduce.jobhistory.address</name>
  <value>historyserver:10020</value>
</property>

db.collection.insertOne({name: "Alice", status: "active"})
db.collection.updateOne({_id: id}, {$set: {status: "inactive"}})
db.collection.deleteOne({_id: id})
db.collection.find({age: {$gt: 30}}).sort({name: 1})
db.collection.createIndex({email: 1}, {unique: true})
db.collection.createIndex({location: "2dsphere"})
db.logs = db.createCollection("logs", {capped: true, size: 104857600}) // 100MB cap

Driver: spark.submit → YARN → ApplicationMaster
        → DAG Scheduler → Task Scheduler
        → Executors launched (on YARN containers)
        → Tasks run → Shuffle → Result back to driver

// 1. Basic Types
val x: Int = 42            // immutable
var y = "hello"            // mutable
val list = List(1,2,3)
val map = Map("a" -> 1, "b" -> 2)

// 2. Classes & Case Classes (99% of Spark code uses case classes)
case class Person(name: String, age: Int)
val p = Person("Alice", 30)
p.name  // → "Alice"

// 3. Functions & Closures
def add(a: Int, b: Int): Int = a + b
val add5 = (x: Int) => x + 5

// 4. Collections & Higher-Order Functions
val numbers = List(1,2,3,4,5)
numbers.filter(_ % 2 == 1).map(_ * 2)  // → List(2,6,10)

// 5. Pattern Matching (the heart of Scala)
def describe(x: Any): String = x match {
  case i: Int => s"Int $i"
  case s: String => s"String $s"
  case _ => "Unknown"
}

// 6. Implicit (used heavily in Spark SQL)
implicit val timeout = 10
def retry[T](body: => T)(implicit t: Int) = { ... }

// 7. Spark Example (Scala)
val df = spark.read.parquet("/data/sales")
df.filter($"age" > 30)
  .groupBy("country")
  .agg(sum("revenue"))
  .write.mode("overwrite").save("/output/report")

# Full modern stack: HDFS + YARN + Spark 3.5 + Hive + MongoDB + Scala REPL
docker-compose up -d
# → Gets you:
# - HDFS NameNode UI: http://localhost:9870
# - YARN UI: http://localhost:8088
# - Spark History: http://localhost:18080
# - MongoDB: mongodb://localhost:27017
# - Scala REPL ready