protected List<Set<Rule>> buildRuleSets() {
List<Set<Rule>> ls = new ArrayList<Set<Rule>>();
Set<Rule> s = new HashSet<Rule>();
// add split filter rule
Rule r = new PartitionFilterOptimizer("PartitionFilterPushDown");
s = new HashSet<Rule>();
s.add(r);
ls.add(s);
r = new LoadTypeCastInserter( "LoadTypeCastInserter" );