[SPARK-49852][SQL] Fix deadlock caused by explain string generation #48375
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
the pyspark failure is unrelated, thanks, merging to master! |
himadripal
pushed a commit
to himadripal/spark
that referenced
this pull request
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 <ziqi.liu@databricks.com> Signed-off-by: Wenchen Fan <wenchen@databricks.com>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
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