Indexing in Titan/Janus

Question

I have 2 questions:

1. How to index this query?

   g.V(vertexId).repeat(out().hasLabel('location')).emit().tree().next()
   

2. in the Titan 1.0 documentation, there are only ways given to index the graph once when the data is already inserted . However in the generate-modern.groovy file here
   we see that indexing is done before the creation of vertices which seems reasonable. However I am unable to do it when trying to use buildMixedIndex as it is throwing me

   illegal argument exception :Unknown external index backend search

My approach was

def location = mgmt.makeVertexLabel("location").make()
def displayName = mgmt.makePropertyKey("displayName").dataType(String.class).cardinality(Cardinality.SINGLE).make()
def shortName = mgmt.makePropertyKey("shortName").dataType(String.class).cardinality(Cardinality.SINGLE).make()
def description = mgmt.makePropertyKey("description").dataType(String.class).cardinality(Cardinality.SINGLE).make()
def latitude = mgmt.makePropertyKey("latitude").dataType(String.class).cardinality(Cardinality.SINGLE).make()
def longitude = mgmt.makePropertyKey("longitude").dataType(String.class).cardinality(Cardinality.SINGLE).make()

def locationByName = mgmt.buildIndex("displayNameAndShortNameAndDescriptionAndLatitudeAndLongitude", Vertex.class).addKey(displayName).addKey(shortName).addKey(description)
.addKey(latitude).addKey(longitude).indexOnly(location).buildMixedIndex('search')

Where I am getting it wrong?

Answer 1

1. If that query is taking a long time, the problem is likely that it is visiting too many elements or it is stuck in an infinite loop. The existing JanusGraph/Titan indexes won't help for that. You already have a direct vertex lookup by id, g.V(vertexId), and the rest of the query is traversing the neighborhood from that vertex. I'd suggest using edge labels, i.e. out('friends'), to limit the number of edges you visit. You could also use simplePath() to eliminate cyclic paths. You could also use times() or until() to keep a limit on the number of times you loop with the repeat() step.

2. The configuration example you referenced only used composite indexes, which do not require an indexing backend.

Mixed indexes require configuring an indexing backend, either Elasticsearch, Lucene, or Solr. Pick one of these, then make sure you pass the correct configuration properties when you initialize your graph. You can find several examples in the distribution zip file in the conf directory. For example, in the janusgraph-cassandra-es.properties, you'll find:

index.search.backend=elasticsearch
index.search.hostname=127.0.0.1
index.search.elasticsearch.client-only=true

where search in index.X.backend is the chosen index configuration name you must pass to buildMixedIndex(X).