[jira] [Assigned] (HIVE-22079) Post order walker for iterating over expression tree

["Vineet Garg (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-22079?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vineet Garg reassigned HIVE-22079:
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> 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
>            Priority: Major
>
> 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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