Affects Version/s: None
Fix Version/s: 0.4.0
With short circuit evaluation supported for boolean and/or operators (
DRILL-937), we could further optimize boolean and/or operators by re-ordering the evaluation sequence and choose to evaluate the cheapest test first.
For instance, consider we have the following expression :
really_slow_test ( ...) && slower_test ( ...) && fast_test ( ...)
If we choose to evaluate really_slow_test(() first, we will do such test for every input. In contrast, if we choose do fast_test() first, we could skip the evaluation of slower_test() and really_slow_test(), if some input fails at the fast_test(). That is, performance would be better, if we transform the expression into:
fast_test(..) && slower_test(...) && really_slow_test (....).
To add such support, we need do :
1. Change the boolean "and"/"or" so that it takes arbitrary number of operands. ( Previously, "and"/"or" is processed as taking two operands) This way, we could compare and sort all the operands under one single "and"/"or" operator.
2. Assign a cost category to different functions/operators, to reflect the rough estimation of each individual function/operator.
3. Re-order the operands based on the cumulative cost for evaluation.