Jena native store indexes

[Laura Morales]

With RDBMSes, indexes are a bit topic and should always be taken into 
consideration when writing queries. With RDF stores instead, I barely see them 
mentioned at all. So I was wondering how indexes work in Jena native store, or 
other native stores in general. When writing SPARQL queries, should I be aware 
of any particular index? Should I create new indexes myself (how)?