tinkerpop3 - Indexing fails on enabling force index in Titan/Janus -

i've written junit test check against generate-modern.groovy graph if marko exists.
gremlin query being

"g.v().has('name','marko')";

as can see in generate-modern.groovy file indexing applied on name property of person. later made following

query.force-index=true

property true in dynamodb.properties file blocks whole graph scan thereby making indexing mandatory. throws me following exception

org.janusgraph.core.janusgraphexception: not find suitable index answer graph query , graph scans disabled: [(name = marko)]:vertex 

the above exception raised following standardjanusgraphtx class's method

    @override     public iterator<janusgraphelement> execute(final graphcentricquery query, final jointindexquery indexquery, final object exeinfo, final queryprofiler profiler) {         iterator<janusgraphelement> iter;         if (!indexquery.isempty()) {             list<queryutil.indexcall<object>> retrievals = new arraylist<queryutil.indexcall<object>>();             (int = 0; < indexquery.size(); i++) {                 final jointindexquery.subquery subquery = indexquery.getquery(i);                  retrievals.add(new queryutil.indexcall<object>() {                     @override                     public collection<object> call(int limit) {                         final jointindexquery.subquery adjustedquery = subquery.updatelimit(limit);                         try {                             return indexcache.get(adjustedquery, new callable<list<object>>() {                                 @override                                 public list<object> call() throws exception {                                     return queryprofiler.profile(subquery.getprofiler(), adjustedquery, q -> indexserializer.query(q, txhandle));                                 }                             });                         } catch (exception e) {                             throw new janusgraphexception("could not call index", e.getcause());                         }                     }                 });             }               list<object> resultset = queryutil.processintersectingretrievals(retrievals, indexquery.getlimit());             iter = com.google.common.collect.iterators.transform(resultset.iterator(), getconversionfunction(query.getresulttype()));         } else {             if (config.hasforceindexusage()) throw new janusgraphexception("could not find suitable index answer graph query , graph scans disabled: " + query);             log.warn("query requires iterating on vertices [{}]. better performance, use indexes", query.getcondition());              queryprofiler sub = profiler.addnested("scan");             sub.setannotation(queryprofiler.query_annotation,indexquery);             sub.setannotation(queryprofiler.fullscan_annotation,true);             sub.setannotation(queryprofiler.condition_annotation,query.getresulttype());              switch (query.getresulttype()) {                 case vertex:                     return (iterator) getvertices().iterator();                  case edge:                     return (iterator) getedges().iterator();                  case property:                     return new vertexcentricedgeiterable(getinternalvertices(),relationcategory.property).iterator();                  default:                     throw new illegalargumentexception("unexpected type: " + query.getresulttype());             }         }          return iter;     }  }; 

as can observe method exception raised when jointindexquery object empty(arraylist being empty) , force index true.
the problem why list empty? when have specified indexing query against name property in generate-modern.groovy while querying junit test.this works fine meaning list not empty when same data being preloaded gremlin server same file.

the personbyname index definition uses label constraint.

def personbyname = mgmt.buildindex("personbyname", vertex.class).addkey(name).indexonly(person).buildcompositeindex() 

in order take advantage of index, must use label , property. example:

g.v().has('person', 'name', 'marko') 

you can read more in janusgraph documentation http://docs.janusgraph.org/latest/indexes.html#_label_constraint