Vineet Garg created HIVE-22079:
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Summary: Post order walker for iterating over expression tree
Key: HIVE-22079
URL: https://issues.apache.org/jira/browse/HIVE-22079
Project: Hive
Issue Type: Improvement
Components: Logical Optimizer, Physical Optimizer
Affects Versions: 4.0.0
Reporter: Vineet Garg
Assignee: Vineet Garg
Current {{DefaultGraphWalker}} is used to iterate over an expression tree. This
walker uses hash map to keep track of visited/processed nodes. If an expression
tree is large this adds significant overhead due to map lookup.
For an expression trees we can instead use post order traversal and avoid using
map.
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