Hello Kafka Graphs

Creating Graphs

A graph in Kafka Graphs is represented by two tables from Kafka Streams, one for vertices and one for edges. The vertex table is comprised of an ID and a vertex value, while the edge table is comprised of a source ID, target ID, and edge value.

KTable<Long, Long> vertices = ...
KTable<Edge<Long>, Long> edges = ...
KGraph<Long, Long, Long> graph = new KGraph<>(
    vertices,
    edges,
    GraphSerialized.with(Serdes.Long(), Serdes.Long(), Serdes.Long())
);

For example, in the class TestGraphUtils we define the following graph

• Its vertex are defined by:

  1,1
  2,2
  3,3
  4,4
  5,5
  6,6
  

• Its edges are defined by:

  1,2,12
  1,3,13
  2,3,23
  3,4,34
  3,6,36
  4,5,45
  4,6,46
  5,6,56
  6,1,61
  

Graph Operations

Kafka Graphs provides a number of APIs for transforming graphs in the same manner as Apache Flink Gelly and Apache Spark GraphX.

• Filtering methods
  • filterOnEdges
  • filterOnVertices
  • subgraph
• Joining methods
  • joinWithEdges
  • joinWithEdgesOnSource
  • joinWithEdgesOnTarget
  • joinWithVertices
• Mapping methods
  • mapEdges
  • mapVertices
• Reducing methods
  • groupReduceOnEdges
  • groupReduceOnNeighbors
  • reduceOnEdges
  • reduceOnNeighbors
• Transforming methods
  • inDegrees
  • outDegrees
  • undirected

For example, the following will compute the sum of the values of all incoming neighbors for each vertex.

graph.reduceOnNeighbors(new SumValues(), EdgeDirection.IN);

Running Graph Operations

In the class GraphOperations we run the Operations over the defined Graph

• The method testOutDegrees()

  Calculates KTable<Long, Long> outDegrees = graph.outDegrees();

  The result is the out-degree of each vertex:

  1,2
  2,1
  3,2
  4,2
  5,1
  6,1
  

• The method testInDegrees()

  Calculates KTable<Long, Long> inDegrees = graph.inDegrees();

  The result is the in-degree of each vertex:

  1,1
  2,1
  3,2
  4,1
  5,1
  6,3
  

• The method testUndirected()

  Calculates KTable<Edge<Long>, Long> data = graph.undirected().edges();

  The result is the all the edges without considering direction:

  1,2,12    2,1,12
  1,3,13    3,1,13
  2,3,23    3,2,23
  3,4,34    4,3,34
  3,6,36    6,3,36
  4,5,45    5,4,45
  4,6,46    6,4,46
  5,6,56    6,5,56
  6,1,61    1,6,61
  

• The method testSubGraph()

  Calculates KTable<Edge<Long>, Long> data = graph.subgraph((k, v) -> v > 2, (k, e) -> e > 34).edges();

  The result is all the edges with vertex greater than 2 and edge greater than 34:

  3,6,36
  4,5,45
  4,6,46
  5,6,56
  

• The method testFilterVertices()

  Calculates KTable<Edge<Long>, Long> data = graph.filterOnVertices((k, v) -> v > 2).edges();

  The result are all the vertex greater that 2:

  3,4,34
  3,6,36
  4,5,45
  4,6,46
  5,6,56
  

• The method testFilterEdges()

  Calculates KTable<Edge<Long>, Long> data = graph.filterOnEdges((k, e) -> e > 34).edges();

  The result are all the edges greater than 34:

  4,5,45
  4,6,46
  5,6,56
  6,1,61