[SPARK-49852][SQL] Fix deadlock caused by explain string generation #48375
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the pyspark failure is unrelated, thanks, merging to master! |
himadripal
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Oct 19, 2024
### What changes were proposed in this pull request? Replace `TreeNode.allChildren` with identity map (which was `Set` previously) to avoid hashcode lazy evalution. ### Why are the changes needed? We hit a deadlock between shuffle dependency initialization and explain string generation, in which both code paths trigger lazy variable instantiation while visiting some tree nodes in different orders and thus acquiring object locks in a reversed order. The hashcode of plan node is implemented as lazy val. So the fix is to remove hash code computation from explain string generation so to break the chain of lazy variable instantiation. `TreeNode.allChildren` is only used in explain string generation and only require identity equality. This should be also a small perforamance improvement BTW. ### Does this PR introduce _any_ user-facing change? NO ### How was this patch tested? Current UTs ### Was this patch authored or co-authored using generative AI tooling? NO Closes apache#48375 from liuzqt/SPARK-49852. Authored-by: Ziqi Liu <[email protected]> Signed-off-by: Wenchen Fan <[email protected]>
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What changes were proposed in this pull request?
Replace
TreeNode.allChildrenwith identity map (which wasSetpreviously) to avoid hashcode lazy evalution.Why are the changes needed?
We hit a deadlock between shuffle dependency initialization and explain string generation, in which both code paths trigger lazy variable instantiation while visiting some tree nodes in different orders and thus acquiring object locks in a reversed order.
The hashcode of plan node is implemented as lazy val. So the fix is to remove hash code computation from explain string generation so to break the chain of lazy variable instantiation.
TreeNode.allChildrenis only used in explain string generation and only require identity equality. This should be also a small perforamance improvement BTW.Does this PR introduce any user-facing change?
NO
How was this patch tested?
Current UTs
Was this patch authored or co-authored using generative AI tooling?
NO