cmu-db / peloton / 6284

75%

master: 77%

Pull #1494

travis-ci

Refactoring + full tree rebuilding (at least 2 levels work)

What still doesn't work/don't care about yet/not done
- proper memory management (terrier uses shared_ptr anyways)

- other 1-level rewrites, multi-layer rewrites, other expr rewrites

- how can we define a grammar to programmatically create these rewrites?
  (the one we have is way too static...)

- in relation to logical equivalence:
  (1) how do we generate logically equivalent expressions:
      - multi-pass using generating rules (similar to ApplyRule) OR
      - from Pattern A, generate logically equivalent set of patterns P OR
      - transform input expression to match certain specification OR
      - ???
  (2) what operators do we support translating?
      - probably (a AND b) ====> (b AND a)
      - probably (a OR b) ====> (b OR a)
      - probably (a = b) ====> (b = a)
      - maybe more???
  (3) do we want multi level translations?
      - i.e (a AND b) AND c ====> (a AND (b AND c))
      - what order do we do these in?
  May have to modify these operations:
  - Some assertions in TopDownRewrite/BottomUpRewrite w.r.t to the iterator
  - Possibly binding.cpp / optimizer_metadata.h / optimizer_task.cpp

Issues still pending:
- Comparing Values (Matt email/discussion)
- r.rule->Check (terrier issue #332)

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