[GitHub] gatorsmile commented on issue #23759: [SPARK-26840][SQL] Avoid cost-based join reorder in presence of join hints

[GitBox <gi...@apache.org>]

gatorsmile commented on issue #23759: [SPARK-26840][SQL] Avoid cost-based join reorder in presence of join hints
URL: https://github.com/apache/spark/pull/23759#issuecomment-463392303
 
 
   I am the reviewer of the original PRs. It takes me many days to finish the review. It is a little bit hard to refactor the whole Hint framework step by step. The goal of the whole hint refactoring is straightforward. We learned the lessons from AnalysisBarrier. Compared with AnalysisBarrier, Hint node is even worse. Users could see the regressions if they use Hint. Not all the the optimizer rules consider Hint when writing the case matching. Basically, the refactoring fixes various issues in the optimizer. The whole work is a very great and benefit all the users in the long term! In the next PR, we can add a new conf for enabling users to decide whether we should throw an exception when the hint is not applicable. Previously, we always silently drop the hints if they do not work. 
   

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