doc = new Document();
addField(doc, groupField, "b", useDv);
addField(doc, "airport", "ams", useDv);
addField(doc, "duration", "10", useDv);
w.addDocument(doc);
w.commit(); // To ensure a second segment
// 3
doc = new Document();
addField(doc, groupField, "b", useDv);
addField(doc, "airport", "ams", useDv);