Package org.apache.lucene.util.hnsw

Class OnHeapHnswGraph

java.lang.Object
org.apache.lucene.util.hnsw.HnswGraph
org.apache.lucene.util.hnsw.OnHeapHnswGraph
All Implemented Interfaces:
Accountable
public final class OnHeapHnswGraph extends HnswGraph implements Accountable
An HnswGraph where all nodes and connections are held in memory. This class is used to construct the HNSW graph before it's written to the index.

  • Method Details

    • getNeighbors

      public NeighborArray getNeighbors(int level, int node)
      Returns the NeighborQueue connected to the given node.
      Parameters:
      level - level of the graph
      node - the node whose neighbors are returned, represented as an ordinal on the level 0.

    • size

      public int size()
      Description copied from class: HnswGraph
      Returns the number of nodes in the graph
      Specified by:
      size in class HnswGraph

    • maxNodeId

      public int maxNodeId()
      When we initialize from another graph, the max node id is different from size(), because we will add nodes out of order, such that we need two method for each
      Overrides:
      maxNodeId in class HnswGraph
      Returns:
      max node id (inclusive)

    • addNode

      public void addNode(int level, int node)
      Add node on the given level. Nodes can be inserted out of order, but it requires that the nodes preceded by the node inserted out of order are eventually added.

      NOTE: You must add a node starting from the node's top level

      Parameters:
      level - level to add a node on
      node - the node to add, represented as an ordinal on the level 0.

    • seek

      public void seek(int level, int targetNode)
      Description copied from class: HnswGraph
      Move the pointer to exactly the given level's target. After this method returns, call HnswGraph.nextNeighbor() to return successive (ordered) connected node ordinals.
      Specified by:
      seek in class HnswGraph
      Parameters:
      level - level of the graph
      targetNode - ordinal of a node in the graph, must be ≥ 0 and < FloatVectorValues.size().

    • nextNeighbor

      public int nextNeighbor()
      Description copied from class: HnswGraph
      Iterates over the neighbor list. It is illegal to call this method after it returns NO_MORE_DOCS without calling HnswGraph.seek(int, int), which resets the iterator.
      Specified by:
      nextNeighbor in class HnswGraph
      Returns:
      a node ordinal in the graph, or NO_MORE_DOCS if the iteration is complete.

    • numLevels

      public int numLevels()
      Returns the current number of levels in the graph
      Specified by:
      numLevels in class HnswGraph
      Returns:
      the current number of levels in the graph

    • entryNode

      public int entryNode()
      Returns the graph's current entry node on the top level shown as ordinals of the nodes on 0th level
      Specified by:
      entryNode in class HnswGraph
      Returns:
      the graph's current entry node on the top level

    • trySetNewEntryNode

      public boolean trySetNewEntryNode(int node, int level)
      Try to set the entry node if the graph does not have one
      Returns:
      True if the entry node is set to the provided node. False if the entry node already exists

    • tryPromoteNewEntryNode

      public boolean tryPromoteNewEntryNode(int node, int level, int expectOldLevel)
      Try to promote the provided node to the entry node
      Parameters:
      level - should be larger than expectedOldLevel
      expectOldLevel - is the old entry node level the caller expect to be, the actual graph level can be different due to concurrent modification
      Returns:
      True if the entry node is set to the provided node. False if expectOldLevel is not the same as the current entry node level. Even if the provided node's level is still higher than the current entry node level, the new entry node will not be set and false will be returned.

    • getNodesOnLevel

      public HnswGraph.NodesIterator getNodesOnLevel(int level)
      WARN: calling this method will essentially iterate through all nodes at level 0 (even if you're not getting node at level 0), we have built some caching mechanism such that if graph is not changed only the first non-zero level call will pay the cost. So it is highly NOT recommended to call this method while the graph is still building.

      NOTE: calling this method while the graph is still building is prohibited

      Specified by:
      getNodesOnLevel in class HnswGraph
      Parameters:
      level - level for which to get all nodes
      Returns:
      an iterator over nodes where nextInt returns a next node on the level

    • ramBytesUsed

      public long ramBytesUsed()
      Description copied from interface: Accountable
      Return the memory usage of this object in bytes. Negative values are illegal.
      Specified by:
      ramBytesUsed in interface Accountable

    • toString

      public String toString()
      Overrides:
      toString in class Object