CODEWITHSUNDEEP
cassandragraph-theorytinkerpop3janusgraph
kolokol13
kolokol13

Reputation: 31

Can't see my vertex and edge from my Graph instance but able to see from other graph instance

Working on a proof of concept if I add vertex and edge using the Graph instance inside my application and then I query those sometimes the query result send me the vertex and edge and sometimes doesn't, but if I create a JUnit test pointing to the server I'm able to see the vertex and edge persisted. Same happen if I drop a vertex or a edge

What I'm missing?

============= Class to work with Vertex and Edge =================

public class JanusGraphRepository implements GraphRepository {

    private Graph graph;
    private GraphTraversalSource g;

    public JanusGraphRepository(Graph janusGraph) {
        this.graph = janusGraph;
        this.g = graph.traversal();
    }

    @Override
    public void dropE(Object id) {
        g.E(id).drop().iterate();
        g.tx().commit();
    }

    @Override
    public void dropV(Object id) {
        g.V(id).drop().iterate();
        g.tx().commit();
    }

    @Override
    public Vertex addV(final Object... keyValues) {
        Vertex v = graph.addVertex(keyValues);
        graph.tx().commit();
        return v;
    }

    @Override
    public Edge addE(String edgeLabel, Object fromVertex, Object toVertex,
            Object... keyValues) {
        Edge e = graph.vertices(fromVertex).next().addEdge(edgeLabel,
                graph.vertices(toVertex).next(), keyValues);
        graph.tx().commit();
        return e;
    }
}


======================== Code to get vertices and edges ======================

JanusGraphFactory.Builder config = JanusGraphFactory.build();
        config.set("storage.backend", "cql");
        config.set("storage.hostname", "10.2.1.134");
        config.set("storage.cql.keyspace", "janusgraph");
        config.set("index.search.backend", "elasticsearch");
        config.set("index.search.hostname", "10.2.1.134");
        // config.set("index.search.elasticsearch.client-only", "true");
        // ip address where cassandra is installed
        // config.set("storage.username", "cassandra");
        // config.set("storage.password", "cassandra");
        // config.set("storage.port", "8182");

        // Get the instance of graph
        JanusGraph graph = config.open();

        graph.vertices().forEachRemaining(x -> {
            System.out.println(x.id());
        });
        System.out.println("------ Edges -------");
        graph.edges().forEachRemaining(x -> {
            System.out.println(x.toString());
        });


Thanks

Upvotes: 3

Views: 194

Answers (1)

Rebecca Nelson
Rebecca Nelson

Reputation: 1296

Mutations in Cassandra are not guaranteed to be instantly visible.

I see that you are using the CQL storage backend for Janus, which tells me you are using a Cassandra node/cluster. In Cassandra, writes are required to propagate to each node, and might not happen immediately. It sounds like you might be experiencing this.

Especially in the case where a particular write needs to be passed along to the node that owns its index range, and subsequent reads end up reading from that node, it is possible to get into a situation where a write followed by an immediate read does not show the data that was just written.

The time that it takes for the write to appear depends on a variety of factors in the Cassandra cluster; generally, it shouldn't take more than a few minutes even at very high scale, but this is not guaranteed. Cassandra prioritizes availability over the consistency of mutations. As long as the cluster remains online and operational, mutations will make it to all replicas within a cluster eventually, but not necessarily at the time that the write call returns. This behavior is known as eventual consistency.

In order to get around this, you must adjust your expectations; you cannot expect data that was just written to the cluster (and therefore JanusGraph when using Cassandra as a backend) to be immediately available.

If your use-case cannot work with Cassandra's model of consistency, I'd suggest taking a look at HBase or one of the other backends listed in the Storage Backends Section of the JanusGraph Manual.

Upvotes: 3

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