Hey everyone,

I'm currently running janusgraph-inmemory with janusgraph-lucence both version 0.6.2
And I'm experiencing strange behaviour when creating an index that contains an underscore in its name.
Whenever I run the following code:

PropertiesConfiguration conf = ConfigurationUtil.loadPropertiesConfig("conf/test.properties");
JanusGraph graph = JanusGraphFactory.open(conf);
String name = "some_name";

graph.tx().rollback();
JanusGraphManagement management = graph.openManagement();

management.makePropertyKey("name").dataType(String.class).make();
management.commit();

management = graph.openManagement();

management.buildIndex(name, Vertex.class)
        .addKey(management.getPropertyKey("name"))
        .buildMixedIndex("search");
management.commit();

ManagementSystem.awaitGraphIndexStatus(graph, name).
        status(SchemaStatus.REGISTERED)
        .call();

management = graph.openManagement();
management.updateIndex(management.getGraphIndex(name), SchemaAction.REINDEX).get();
management.commit();

management = graph.openManagement();
System.out.println(management.printIndexes());

graph.traversal().addV().property("name", "Test").next();
graph.tx().commit();

I get the following output:

INFO  o.j.g.d.management.ManagementSystem - Index update job successful for [some_name]
------------------------------------------------------------------------------------------------
Graph Index (Vertex)           | Type        | Unique    | Backing        | Key:           Status |
---------------------------------------------------------------------------------------------------
some_name                      | Mixed       | false     | search         | name:         ENABLED |
---------------------------------------------------------------------------------------------------
Graph Index (Edge)             | Type        | Unique    | Backing        | Key:           Status |
---------------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------------
Relation Index (VCI)           | Type        | Direction | Sort Key       | Order    |     Status |
---------------------------------------------------------------------------------------------------

ERROR o.j.g.database.StandardJanusGraph - Error while committing index mutations for transaction [5] on index: search
org.janusgraph.core.JanusGraphException: Could not execute operation due to backend exception
	at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:54)
	at org.janusgraph.diskstorage.indexing.IndexTransaction.flushInternal(IndexTransaction.java:158)
	at org.janusgraph.diskstorage.indexing.IndexTransaction.commit(IndexTransaction.java:139)
	at org.janusgraph.diskstorage.BackendTransaction.commitIndexes(BackendTransaction.java:143)
	at org.janusgraph.graphdb.database.StandardJanusGraph.commit(StandardJanusGraph.java:804)
	at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.commit(StandardJanusGraphTx.java:1525)
	at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsGraph$GraphTransaction.doCommit(JanusGraphBlueprintsGraph.java:322)
	at org.apache.tinkerpop.gremlin.structure.util.AbstractTransaction.commit(AbstractTransaction.java:104)
	at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsGraph$GraphTransaction.commit(JanusGraphBlueprintsGraph.java:300)
	at Scratch.main(scratch.java:48)
Caused by: org.janusgraph.diskstorage.PermanentBackendException: Permanent exception while executing backend operation IndexMutation
	at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:79)
	at org.janusgraph.diskstorage.util.BackendOperation.execute(BackendOperation.java:52)
	... 9 common frames omitted
Caused by: java.lang.IllegalArgumentException: Invalid store name: some_name
	at com.google.common.base.Preconditions.checkArgument(Preconditions.java:217)
	at org.janusgraph.diskstorage.lucene.LuceneIndex.getStoreDirectory(LuceneIndex.java:194)
	at org.janusgraph.diskstorage.lucene.LuceneIndex.getWriter(LuceneIndex.java:216)
	at org.janusgraph.diskstorage.lucene.LuceneIndex.mutateStores(LuceneIndex.java:289)
	at org.janusgraph.diskstorage.lucene.LuceneIndex.mutate(LuceneIndex.java:275)
	at org.janusgraph.diskstorage.indexing.IndexTransaction$1.call(IndexTransaction.java:161)
	at org.janusgraph.diskstorage.indexing.IndexTransaction$1.call(IndexTransaction.java:158)
	at org.janusgraph.diskstorage.util.BackendOperation.executeDirect(BackendOperation.java:66)
	... 10 common frames omitted

Wouldn't it be better to disallow the creation of the index in the first place? After the creation all queries seem to fail with the same PermanentBackendException.

Also I don't quite understand why underscores are not allowed in index names. Maybe this is a limitation of Lucene