Vineet Garg updated HIVE-22079:
    Status: Patch Available  (was: Open)

> 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
>         Attachments: HIVE-22079.1.patch, HIVE-22079.2.patch, 
> HIVE-22079.3.patch, HIVE-22079.4.patch
> 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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