core: add iterator to TagIndex (#1705)

Add iterator method for traversing all entries in the
index without needing to materialize the result set.
Mostly intended for debugging use-cases.

atlas-core/src/main/scala/com/netflix/atlas/core/index/BatchUpdateTagIndex.scala

@@ -143,5 +143,7 @@ class BatchUpdateTagIndex[T <: TaggedItem: ClassTag](
 
   def findItems(query: TagQuery): List[T] = currentIndex.get.findItems(query)
 
+  override def iterator: Iterator[T] = currentIndex.get.iterator
+
   def size: Int = currentIndex.get.size
 }

atlas-core/src/main/scala/com/netflix/atlas/core/index/CachingTagIndex.scala

@@ -57,5 +57,7 @@ class CachingTagIndex[T <: TaggedItem](delegate: TagIndex[T]) extends TagIndex[T
     findItemsCache.get(query)
   }
 
+  override def iterator: Iterator[T] = delegate.iterator
+
   def size: Int = delegate.size
 }

atlas-core/src/main/scala/com/netflix/atlas/core/index/RoaringTagIndex.scala

@@ -495,6 +495,8 @@ class RoaringTagIndex[T <: TaggedItem](items: Array[T], stats: IndexStats) exten
     result.result()
   }
 
+  override def iterator: Iterator[T] = items.iterator
+
   val size: Int = items.length
 }
 

atlas-core/src/main/scala/com/netflix/atlas/core/index/SimpleTagIndex.scala

@@ -135,6 +135,8 @@ class SimpleTagIndex[T <: TaggedItem: ClassTag](items: Array[T]) extends TagInde
     sorted.take(query.limit)
   }
 
+  override def iterator: Iterator[T] = items.iterator
+
   val size: Int = items.length
 
   def update(additions: List[T], deletions: List[ItemId]): TagIndex[T] = {

atlas-core/src/main/scala/com/netflix/atlas/core/index/TagIndex.scala

@@ -28,6 +28,8 @@ trait TagIndex[T <: TaggedItem] {
 
   def findItems(query: TagQuery): List[T]
 
+  def iterator: Iterator[T]
+
   def size: Int
 }
 

atlas-core/src/test/scala/com/netflix/atlas/core/index/TagIndexSuite.scala

@@ -347,4 +347,10 @@ abstract class TagIndexSuite extends FunSuite {
     }
     assertEquals(result.size, 4640)
   }
+
+  test("iterator") {
+    val expected = index.findItems(TagQuery(Some(Query.True))).map(_.tags.toString).sorted
+    val actual = index.iterator.map(_.tags.toString).toList.sorted
+    assertEquals(actual, expected)
+  }
 }

atlas-postgres/src/main/scala/com/netflix/atlas/postgres/PostgresTagIndex.scala

@@ -84,7 +84,11 @@ class PostgresTagIndex(postgres: PostgresService) extends TagIndex[TaggedItem] {
   }
 
   override def findItems(query: TagQuery): List[TaggedItem] = {
-    throw new UnsupportedOperationException("")
+    throw new UnsupportedOperationException("findItems")
+  }
+
+  override def iterator: Iterator[TaggedItem] = {
+    throw new UnsupportedOperationException("iterator")
   }
 
   override def size: Int = 0