LogicalPlanOptimizer optimizer = new LogicalPlanOptimizer( plan, 100, optimizerRules );
optimizer.optimize();
// compute whether output data is sorted or not
SortInfoSetter sortInfoSetter = new SortInfoSetter( plan );
sortInfoSetter.visit();
if (pigContext.inExplain==false) {
// Validate input/output file. Currently no validation framework in
// new logical plan, put this validator here first.
// We might decide to move it out to a validator framework in future