[GitHub] [spark] cloud-fan opened a new pull request #24735: [SPARK-27871][SQL] LambdaVariable should use per-query unique IDs instead of globally unique IDs

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

cloud-fan opened a new pull request #24735: [SPARK-27871][SQL] LambdaVariable should use per-query unique IDs instead of globally unique IDs
URL: https://github.com/apache/spark/pull/24735
 
 
   ## What changes were proposed in this pull request?
   
   For simplicity, all `LambdaVariable`s are globally unique, to avoid any potential conflicts. However, this causes a perf problem: we can never hit codegen cache for encoder expressions that deal with collections (which means they contain `LambdaVariable`).
   
   To overcome this problem, `LambdaVariable` should have per-query unique IDs. This PR does 2 things:
   1. refactor `LambdaVariable` to carry an ID, so that it's easier to change the ID.
   2. add an optimizer rule to reassign `LambdaVariable` IDs, which are per-query unique.
   
   ## How was this patch tested?
   
   new tests
   

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