@Override
protected Index<String, Long> createIndex() throws Exception {
Transaction tx = pf.tx();
long id = tx.allocate().getPageId();
tx.commit();
BTreeIndex<String, Long> index = new BTreeIndex<String, Long>(pf, id);
index.setKeyMarshaller(StringMarshaller.INSTANCE);
index.setValueMarshaller(LongMarshaller.INSTANCE);