Array Based Dynamic Graph

cassovary-core/src/main/scala/com/twitter/cassovary/graph/ArrayBasedDynamicDirectedGraph.scala

@@ -0,0 +1,206 @@
+package com.twitter.cassovary.graph
+
+import com.twitter.cassovary.graph.node.DynamicNode
+import it.unimi.dsi.fastutil.ints.IntArrayList
+import scala.collection.mutable.ArrayBuffer
+import StoredGraphDir._
+import com.twitter.cassovary.util.FastUtilUtils
+
+/**
+ * A dynamic directed graph, implemented using an ArrayBuffer of IntArrayList
+ * (from the fastutil library).  If n nodes are used, O(n) objects are created,
+ * independent of the number of edges.
+ *
+ * For efficiency, it's recommended that ids be sequentially numbered, as
+ * an internal array is stored which is longer than the maximum id seen.
+ *
+ * This class is not threadsafe.  If multiple thread access it simultaneously
+ * and at least one mutates it, synchronization should be used.
+ */
+class ArrayBasedDynamicDirectedGraph(override val storedGraphDir: StoredGraphDir)
+    extends DynamicDirectedGraph {
+  // outboundLists(id) contains the outbound neighbors of the given id,
+  // or null if the id is not in this graph.
+  // If we aren't storing outbound neighbors, outboundLists will always remain size 0.
+  private val outboundLists = new ArrayBuffer[IntArrayList]
+  // (See above note on outboundLists)
+  private val inboundLists = new ArrayBuffer[IntArrayList]
+
+  private var nodeCount_ = 0
+
+  def this(dataIterator: Iterator[NodeIdEdgesMaxId],
+            storedGraphDir: StoredGraphDir) {
+    this(storedGraphDir)
+    for (nodeData <- dataIterator) {
+      val id = nodeData.id
+      getOrCreateNode(id)
+      nodeData.edges map getOrCreateNode
+      storedGraphDir match {
+        case OnlyOut => outboundLists(id).addAll(IntArrayList.wrap(nodeData.edges))
+        case OnlyIn => inboundLists(id).addAll(IntArrayList.wrap(nodeData.edges))
+        case BothInOut => nodeData.edges map { addEdgeAllowingDuplicates(id, _) } // Duplicates shouldn't exist, but allow them for efficiency.
+      }
+    }
+  }
+
+  def this(iteratorSeq: Seq[() => Iterator[NodeIdEdgesMaxId]],
+           storedGraphDir: StoredGraphDir) {
+    this((iteratorSeq map { _()} ).iterator.flatten, storedGraphDir)
+  }
+
+  /* Returns an option which is non-empty if outbound list for id  is non-null. */
+  private def outboundListOption(id: Int): Option[IntArrayList] =
+    if (id < 0 || id >= outboundLists.size)
+      None
+  else
+      Option(outboundLists(id)) // If list is null, convert to None
+
+  private def inboundListOption(id: Int): Option[IntArrayList] =
+    if (id < 0 || id >= inboundLists.size)
+      None
+    else
+      Option(inboundLists(id)) // If list is null, convert to None
+
+  /** Wraps outboundList and inboundList in a node structure.  This is an inner class
+    * because mutations will affect other nodes of the graph if both inbound
+    * and outbound neighbor lists are stored.
+    *
+    * For efficiency, we don't store Nodes, but create them on the fly as needed.
+    */
+  class IntListNode(override val id: Int,
+                    val outboundList: Option[IntArrayList],
+                    val inboundList: Option[IntArrayList])
+      extends DynamicNode {
+    override def outboundNodes(): Seq[Int] = outboundList match {
+      case Some(list) => FastUtilUtils.intArrayListToSeq(list)
+      case None => Seq.empty[Int]
+    }
+
+    override def inboundNodes(): Seq[Int] = inboundList match {
+      case Some(list) => FastUtilUtils.intArrayListToSeq(list)
+      case None => Seq.empty[Int]
+    }
+
+    def addOutBoundNodes(nodeIds: Seq[Int]): Unit = {
+      //For future optimization, we could check if we are only storing outbound
+      // nodes and then do:
+      // outboundList.get.addAll(IntArrayList.wrap(nodeIds.toArray))
+      nodeIds map { addEdge(id, _) }
+    }
+
+    def addInBoundNodes(nodeIds: Seq[Int]): Unit = {
+      nodeIds map { addEdge(_, id) }
+    }
+
+    def removeOutBoundNode(nodeId: Int): Unit = removeEdge(id, nodeId)
+
+    def removeInBoundNode(nodeId: Int): Unit =  removeEdge(nodeId, id)
+  }
+
+  /**
+   * Determine if a node with the given id exists in this graph.
+   */
+  def nodeExists(id: Int): Boolean =
+    outboundListOption(id).nonEmpty || inboundListOption(id).nonEmpty
+
+  /**
+   * Returns the node with the given {@code id} or else {@code None} if the given node does not
+   * exist in this graph.
+   */
+  override def getNodeById(id: Int): Option[DynamicNode] =
+    if (nodeExists(id)) {
+      Some(new IntListNode(id, outboundListOption(id), inboundListOption(id)))
+    } else {
+      None
+    }
+
+  override def iterator: Iterator[Node] = (0 until maxIdBound).iterator flatMap getNodeById
+
+  /**
+   * Returns the total number of directed edges in the graph.  A mutual edge, eg: A -> B and B -> A,
+   * counts as 2 edges in this total.
+   */
+  override def edgeCount: Long =
+    if (StoredGraphDir.isOutDirStored(storedGraphDir))
+      (iterator map {_.outboundCount }).sum
+    else
+      (iterator map {_.inboundCount }).sum
+
+  /**
+   * Returns the number of nodes in the graph.
+   */
+  override def nodeCount: Int = nodeCount_
+  // Or this can be computed as (0 until maxIdBound) count nodeExists
+
+  /**
+   * Remove an edge from a {@code srdId} to {@code destId}.
+   * Return Option of source and destination nodes. None indicates the node doesn't exist in graph.
+   */
+  override def removeEdge(srcId: Int, destId: Int): (Option[Node], Option[Node]) = {
+    outboundListOption(srcId) map {list => list.rem(destId)}
+    inboundListOption(destId) map {list => list.rem(srcId)}
+    (getNodeById(srcId), getNodeById(destId))
+  }
+
+  /**
+   * Add an edge from {@code srcId} to {@code destId}.
+   * If the edge already exists, nothing will change. This takes time proportional
+   * to out-degree(srcId) + in-degree(destId).
+   */
+  override def addEdge(srcId: Int, destId: Int): Unit = {
+    getOrCreateNode(srcId)
+    getOrCreateNode(destId)
+    def addIfMissing(list: IntArrayList, k: Int): Unit =
+      if (!list.contains(k))
+        list.add(k)
+    outboundListOption(srcId) map { addIfMissing(_, destId) }
+    inboundListOption(destId) map { addIfMissing(_, srcId) }
+  }
+
+  /**
+   * Add an edge from {@code srcId} to {@code destId}.
+   * If the edge already exists, this will create a parallel edge.  This runs in
+   * constant amortized time.
+   */
+  def addEdgeAllowingDuplicates(srcId: Int, destId: Int): Unit = {
+    getOrCreateNode(srcId)
+    getOrCreateNode(destId)
+    def addIfMissing(list: IntArrayList, id: Int): Unit =
+      if (!list.contains(destId))
+        list.add(destId)
+    outboundListOption(srcId) map { _.add(destId) }
+    inboundListOption(destId) map { _.add(srcId) }
+  }
+
+  /**
+   * Add a node {@code id} into the graph.
+   */
+  override def getOrCreateNode(id: Int): DynamicNode = {
+    def addIdToList(list: ArrayBuffer[IntArrayList]) {
+      if (list.size <= id) {
+        list.appendAll(Array.fill(id - list.size + 1 )(null))
+      }
+      list(id) = new IntArrayList(initialNeighborListCapacity)
+    }
+
+    if (!nodeExists(id)) {
+      nodeCount_ += 1
+      if (StoredGraphDir.isOutDirStored(storedGraphDir)) {
+        addIdToList(outboundLists)
+      }
+      if (StoredGraphDir.isInDirStored(storedGraphDir)) {
+        addIdToList(inboundLists)
+      }
+    }
+
+    getNodeById(id).get
+  }
+
+
+  private def maxIdBound: Int = math.max(outboundLists.size,
+                                         inboundLists.size)
+
+  // This can be overridden if a user knows there will be many nodes with no
+  // neighbors, or if most nodes will have many more than 4 neighbors
+  protected def initialNeighborListCapacity: Int = 4
+}

cassovary-core/src/main/scala/com/twitter/cassovary/util/FastUtilUtils.scala

@@ -16,7 +16,7 @@ package com.twitter.cassovary.util
 
 import java.{util => jutil}
 
-import it.unimi.dsi.fastutil.ints.{Int2BooleanOpenHashMap, Int2IntMap, Int2IntOpenHashMap}
+import it.unimi.dsi.fastutil.ints.{IntArrayList, Int2BooleanOpenHashMap, Int2IntMap, Int2IntOpenHashMap}
 import it.unimi.dsi.fastutil.objects.Object2IntMap
 
 import scala.collection.JavaConversions._
@@ -61,4 +61,6 @@ object FastUtilUtils {
 
   def newInt2IntOpenHashMap(): mutable.Map[Int, Int] =
     new Int2IntOpenHashMap().asInstanceOf[jutil.Map[Int, Int]]
+
+  def intArrayListToSeq(list: IntArrayList): Seq[Int] = list map { _.toInt }
 }

cassovary-core/src/main/scala/com/twitter/cassovary/util/io/GraphReader.scala

@@ -74,4 +74,10 @@ trait GraphReader[T] {
     SharedArrayBasedDirectedGraph(iteratorSeq, executorService, storedGraphDir, numShards)
   }
 
+  /**
+   * Create an `ArrayBasedDynamicDirectedGraph`
+   */
+  def toArrayBasedDynamicDirectedGraph() = {
+    new ArrayBasedDynamicDirectedGraph(iteratorSeq, storedGraphDir)
+  }
 }

cassovary-core/src/test/scala/com/twitter/cassovary/graph/ArrayBasedDynamicDirectedGraphSpec.scala

@@ -0,0 +1,76 @@
+package com.twitter.cassovary.graph
+
+import org.scalatest.WordSpec
+import com.twitter.cassovary.graph.StoredGraphDir._
+import org.scalatest.matchers.ShouldMatchers
+
+class ArrayBasedDynamicDirectedGraphSpec extends WordSpec with ShouldMatchers with GraphBehaviours {
+  def builder(iteratorFunc: () => Iterator[NodeIdEdgesMaxId],
+              storedGraphDir: StoredGraphDir) =
+    new ArrayBasedDynamicDirectedGraph(iteratorFunc(), storedGraphDir)
+  verifyGraphBuilding(builder, sampleGraphEdges)
+
+  "Add new nodes" in {
+    val graph = new ArrayBasedDynamicDirectedGraph(StoredGraphDir.BothInOut)
+    for (i <- 0 until 3) {
+      graph.nodeCount shouldEqual i
+      graph.edgeCount shouldEqual 0
+      graph.getOrCreateNode(10 * i) // non-contiguous
+    }
+    graph.getOrCreateNode(10) // Accessing again should increase node count
+    graph.nodeCount shouldEqual 3
+  }
+
+
+  "Add new edges" in {
+    for (dir <- List(StoredGraphDir.OnlyIn, StoredGraphDir.OnlyOut, StoredGraphDir.BothInOut)) {
+      val graph = new ArrayBasedDynamicDirectedGraph(dir)
+      val inStored = graph.isDirStored(GraphDir.InDir)
+      val outStored = graph.isDirStored(GraphDir.OutDir)
+
+      graph.addEdge(1, 2)
+      graph.addEdge(1, 2) // Test duplicate elimination
+      graph.edgeCount shouldEqual 1
+      val node1 = graph.getNodeById(1).get
+      node1.inboundNodes.toList shouldEqual List()
+      node1.outboundNodes.toList shouldEqual (if(outStored) List(2) else List())
+      val node2 = graph.getNodeById(2).get
+      node2.inboundNodes.toList shouldEqual (if(inStored) List(1) else List())
+      node2.outboundNodes.toList shouldEqual List()
+
+      // Test multi-edge
+      graph.addEdgeAllowingDuplicates(1, 2)
+      graph.edgeCount shouldEqual 2
+      node1.inboundNodes.toList shouldEqual List()
+      node1.outboundNodes.toList shouldEqual (if(outStored) List(2, 2) else List())
+      node2.inboundNodes.toList shouldEqual (if(inStored) List(1, 1) else List())
+      node2.outboundNodes.toList shouldEqual List()
+
+      graph.addEdge(2, 1)
+      graph.edgeCount shouldEqual 3
+    }
+  }
+
+  "Delete edges" in {
+    for (dir <- List(StoredGraphDir.OnlyIn, StoredGraphDir.OnlyOut, StoredGraphDir.BothInOut)) {
+      val graph = new ArrayBasedDynamicDirectedGraph(dir)
+      val inStored = graph.isDirStored(GraphDir.InDir)
+      val outStored = graph.isDirStored(GraphDir.OutDir)
+
+      graph.addEdge(1, 2)
+      graph.addEdge(1, 3)
+      graph.removeEdge(1, 2)
+      graph.edgeCount shouldEqual 1
+      graph.nodeCount shouldEqual 3 // This is debatable but reasonable.
+      val node1 = graph.getNodeById(1).get
+      node1.inboundNodes.toList shouldEqual List()
+      node1.outboundNodes.toList shouldEqual (if(outStored) List(3) else List())
+      val node2 = graph.getNodeById(2).get
+      node2.inboundNodes.toList shouldEqual List()
+      node2.outboundNodes.toList shouldEqual List()
+      val node3 = graph.getNodeById(3).get
+      node3.inboundNodes.toList shouldEqual (if(inStored) List(1) else List())
+      node3.outboundNodes.toList shouldEqual List()
+    }
+  }
+}