IndexReader ireader = DirectoryReader.open(directory); // read-only=true
assert ireader.leaves().size() == 1;
BinaryDocValues dv = ireader.leaves().get(0).reader().getBinaryDocValues("dv");
BytesRef scratch = new BytesRef();
dv.get(0, scratch);
assertEquals("foo!", scratch.utf8ToString());
BytesRef scratch2 = new BytesRef();
dv.get(1, scratch2);
assertEquals("bar!", scratch2.utf8ToString());
// check scratch is still valid