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https://issues.apache.org/jira/browse/HIVE-22079?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16937321#comment-16937321
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Jesus Camacho Rodriguez commented on HIVE-22079:
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+1
> 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
> Labels: pull-request-available
> Attachments: HIVE-22079.1.patch, HIVE-22079.2.patch,
> HIVE-22079.3.patch, HIVE-22079.4.patch, HIVE-22079.5.patch,
> HIVE-22079.6.patch, HIVE-22079.7.patch, HIVE-22079.8.patch
>
> Time Spent: 1h
> Remaining Estimate: 0h
>
> 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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