OnHeapHnswGraph (Lucene 10.5.1 core API)
Description: declaration: package: org.apache.lucene.util.hnsw, class: OnHeapHnswGraph

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.

- ## Nested Class Summary

  ## Nested classes/interfaces inherited from class org.apache.lucene.util.hnsw.HnswGraph

  `HnswGraph.ArrayNodesIterator, HnswGraph.CollectionNodesIterator, HnswGraph.DenseNodesIterator, HnswGraph.NodesIterator`

- ## Field Summary

  ### Fields inherited from class org.apache.lucene.util.hnsw.HnswGraph

  `EMPTY, UNKNOWN_MAX_CONN`

  ### Fields inherited from interface org.apache.lucene.util.Accountable

  `NULL_ACCOUNTABLE`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addNode(int level, int node)`
  Add node on the given level.
  `int`
  `entryNode()`
  Returns the graph's current entry node on the top level shown as ordinals of the nodes on 0th level
  `NeighborArray`
  `getNeighbors(int level, int node)`
  Returns the `NeighborQueue` connected to the given node.
  `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.
  `int`
  `maxConn()`
  returns M, the maximum number of connections for a node.
  `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
  `int`
  `neighborCount()`
  `int`
  `nextNeighbor()`
  Iterates over the neighbor list.
  `boolean`
  `nodeExistAtLevel(int level, int node)`
  `int`
  `numLevels()`
  Returns the current number of levels in the graph
  `long`
  `ramBytesUsed()`
  Provides an estimate of the current on-heap memory usage of the graph.
  `void`
  `seek(int level, int targetNode)`
  Move the pointer to exactly the given `level`'s `target`.
  `int`
  `size()`
  Returns the number of nodes in the graph
  `String`
  `toString()`
  `boolean`
  `tryPromoteNewEntryNode(int node, int level, int expectOldLevel)`
  Try to promote the provided node to the entry node
  `boolean`
  `trySetNewEntryNode(int node, int level)`
  Try to set the entry node if the graph does not have one

  ### Methods inherited from class org.apache.lucene.util.hnsw.HnswGraph

  `getSortedNodes`

  ### Methods inherited from class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

  ### Methods inherited from interface org.apache.lucene.util.Accountable

  `getChildResources`

- ## 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 < `KnnVectorValues.size()`.

  - ### neighborCount

    public int neighborCount()
    Specified by:
      `neighborCount` in class `HnswGraph`

  - ### 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

  - ### nodeExistAtLevel

    public boolean nodeExistAtLevel(int level, int node)

  - ### 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

  - ### maxConn

    public int maxConn()
    Description copied from class: `HnswGraph`
    returns M, the maximum number of connections for a node.
    Specified by:
      `maxConn` in class `HnswGraph`

  - ### 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()
    Provides an estimate of the current on-heap memory usage of the graph. This is not threadsafe, meaning the heap utilization if building the graph concurrently may be inaccurate. The main purpose of this method is during initial document indexing and flush.
    Specified by:
      `ramBytesUsed` in interface `Accountable`

  - ### toString

    public String toString()
    Overrides:
      `toString` in class `Object`