Search Algorithm

• Inverse Transformations (Cycles): detect duplicates, inprogress bit for (expr, physical property vector)
• Exclude physical property annotation.
  e.g. sort A above in the DAG says exclude sort A property below
  no merge join below sort
• Cost Limits: Keep track of failed limits too!
  e.g. No plan with cost < 100 implies no plan with plan < 50 fail quickly