Index with label constraint does not work for partitioned labels

Description

graph = JanusGraphFactory.open("inmemory")
mgmt = graph.openManagement()
l = mgmt.makeVertexLabel('V').partition().make()
p1 = mgmt.makePropertyKey('p').cardinality(Cardinality.SINGLE).dataType(String.class).make()
mgmt.buildIndex("i1", Vertex.class).addKey(p1).indexOnly(l).buildCompositeIndex()
mgmt.commit()
g = graph.traversal()

v1=g.addV("V").property('p','a').next()
g.tx().commit()
g.V().hasLabel('V').has('p', 'a')

gremlin> mgmt = graph.openManagement()
==>org.janusgraph.graphdb.database.management.ManagementSystem@277bc3a5
gremlin> l = mgmt.makeVertexLabel('V').partition().make()
==>V
gremlin> p1 = mgmt.makePropertyKey('p').cardinality(Cardinality.SINGLE).dataType(String.class).make()
==>p
gremlin> mgmt.buildIndex("i1", Vertex.class).addKey(p1).indexOnly(l).buildCompositeIndex()
==>i1
gremlin> mgmt.commit()
==>null
gremlin> g = graph.traversal()
==>graphtraversalsource[standardjanusgraph[inmemory:[127.0.0.1]], standard]
gremlin> 
gremlin> v1=g.addV("V").property('p','a').next()
==>v[4226]
gremlin> g.tx().commit()
==>null
gremlin> g.V().hasLabel('V').has('p', 'a')
gremlin> 

Contributor guide

Tech stack

java

Domain

database

Issue type

bug

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

half day

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

clear

Prerequisites

JavaJanusGraph basicsgraph indexing concepts

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

45

Research direction

Investigate index construction for partitioned vertex labels. The issue provides a clear reproduction script showing composite index 'i1' on property 'p' with indexOnly('V') fails to be used when querying with hasLabel('V') and has('p','a'). Compare with related issue #206. Likely bug in JanusGraph's index handling code, possibly in CompositeIndexType or IndexSerializer. Check the implementation of indexOnly for partitioned labels and ensure the index is properly considered during query planning.